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Merge pull request #7187 from nikomatsakis/issue-3238-defer-reasoning-about-regions

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Defer reasoning about regions until after regionck
This commit is contained in:
Daniel Micay 2013-07-02 14:32:21 -07:00
commit ab34864a30
46 changed files with 2507 additions and 1363 deletions
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3
src/librustc/middle/region.rs
View File

@ -15,6 +15,9 @@ pass builds up the `scope_map`, which describes the parent links in
the region hierarchy. The second pass infers which types must be
region parameterized.
Most of the documentation on regions can be found in
`middle/typeck/infer/region_inference.rs`
*/

52
src/librustc/middle/typeck/check/_match.rs
View File

@ -15,6 +15,7 @@ use middle::typeck::check::demand;
use middle::typeck::check::{check_block, check_expr_has_type, FnCtxt};
use middle::typeck::check::{instantiate_path, lookup_def};
use middle::typeck::check::{structure_of, valid_range_bounds};
use middle::typeck::infer;
use middle::typeck::require_same_types;
use std::hashmap::{HashMap, HashSet};
@ -29,8 +30,8 @@ pub fn check_match(fcx: @mut FnCtxt,
arms: &[ast::arm]) {
let tcx = fcx.ccx.tcx;
let pattern_ty = fcx.infcx().next_ty_var();
check_expr_has_type(fcx, discrim, pattern_ty);
let discrim_ty = fcx.infcx().next_ty_var();
check_expr_has_type(fcx, discrim, discrim_ty);
// Typecheck the patterns first, so that we get types for all the
// bindings.
@ -38,17 +39,22 @@ pub fn check_match(fcx: @mut FnCtxt,
let pcx = pat_ctxt {
fcx: fcx,
map: pat_id_map(tcx.def_map, arm.pats[0]),
match_region: ty::re_scope(expr.id),
block_region: ty::re_scope(arm.body.node.id)
};
for arm.pats.iter().advance |p| { check_pat(&pcx, *p, pattern_ty);}
for arm.pats.iter().advance |p| { check_pat(&pcx, *p, discrim_ty);}
}
// The result of the match is the common supertype of all the
// arms. Start out the value as bottom, since it's the, well,
// bottom the type lattice, and we'll be moving up the lattice as
// we process each arm. (Note that any match with 0 arms is matching
// on any empty type and is therefore unreachable; should the flow
// of execution reach it, we will fail, so bottom is an appropriate
// type in that case)
let mut result_ty = ty::mk_bot();
// Now typecheck the blocks.
let mut result_ty = fcx.infcx().next_ty_var();
let mut arm_non_bot = false;
let mut saw_err = false;
let mut saw_err = ty::type_is_error(discrim_ty);
for arms.iter().advance |arm| {
let mut guard_err = false;
let mut guard_bot = false;
@ -75,26 +81,28 @@ pub fn check_match(fcx: @mut FnCtxt,
else if guard_bot {
fcx.write_bot(arm.body.node.id);
}
else if !ty::type_is_bot(bty) {
arm_non_bot = true; // If the match *may* evaluate to a non-_|_
// expr, the whole thing is non-_|_
}
demand::suptype(fcx, arm.body.span, result_ty, bty);
result_ty =
infer::common_supertype(
fcx.infcx(),
infer::MatchExpression(expr.span),
true, // result_ty is "expected" here
result_ty,
bty);
}
if saw_err {
result_ty = ty::mk_err();
}
else if !arm_non_bot {
} else if ty::type_is_bot(discrim_ty) {
result_ty = ty::mk_bot();
}
fcx.write_ty(expr.id, result_ty);
}
pub struct pat_ctxt {
fcx: @mut FnCtxt,
map: PatIdMap,
match_region: ty::Region, // Region for the match as a whole
block_region: ty::Region, // Region for the block of the arm
}
pub fn check_pat_variant(pcx: &pat_ctxt, pat: @ast::pat, path: @ast::Path,
@ -442,8 +450,8 @@ pub fn check_pat(pcx: &pat_ctxt, pat: @ast::pat, expected: ty::t) {
// then the type of x is &M T where M is the mutability
// and T is the expected type
let region_var =
fcx.infcx().next_region_var_with_lb(
pat.span, pcx.block_region);
fcx.infcx().next_region_var(
infer::PatternRegion(pat.span));
let mt = ty::mt {ty: expected, mutbl: mutbl};
let region_ty = ty::mk_rptr(tcx, region_var, mt);
demand::eqtype(fcx, pat.span, region_ty, typ);
@ -544,9 +552,8 @@ pub fn check_pat(pcx: &pat_ctxt, pat: @ast::pat, expected: ty::t) {
}
ast::pat_vec(ref before, slice, ref after) => {
let default_region_var =
fcx.infcx().next_region_var_with_lb(
pat.span, pcx.block_region
);
fcx.infcx().next_region_var(
infer::PatternRegion(pat.span));
let (elt_type, region_var) = match structure_of(
fcx, pat.span, expected
@ -651,3 +658,4 @@ pub fn check_pointer_pat(pcx: &pat_ctxt,
#[deriving(Eq)]
enum PointerKind { Managed, Send, Borrowed }

4
src/librustc/middle/typeck/check/demand.rs
View File

@ -35,7 +35,7 @@ pub fn suptype_with_fn(fcx: @mut FnCtxt,
ty_a: ty::t, ty_b: ty::t,
handle_err: &fn(span, ty::t, ty::t, &ty::type_err)) {
// n.b.: order of actual, expected is reversed
match infer::mk_subty(fcx.infcx(), b_is_expected, sp,
match infer::mk_subty(fcx.infcx(), b_is_expected, infer::Misc(sp),
ty_b, ty_a) {
result::Ok(()) => { /* ok */ }
result::Err(ref err) => {
@ -45,7 +45,7 @@ pub fn suptype_with_fn(fcx: @mut FnCtxt,
}
pub fn eqtype(fcx: @mut FnCtxt, sp: span, expected: ty::t, actual: ty::t) {
match infer::mk_eqty(fcx.infcx(), false, sp, actual, expected) {
match infer::mk_eqty(fcx.infcx(), false, infer::Misc(sp), actual, expected) {
Ok(()) => { /* ok */ }
Err(ref err) => {
fcx.report_mismatched_types(sp, expected, actual, err);

17
src/librustc/middle/typeck/check/method.rs
View File

@ -619,14 +619,18 @@ impl<'self> LookupContext<'self> {
autoref: None}))
}
ty::ty_rptr(_, self_mt) => {
let region = self.infcx().next_region_var_nb(self.expr.span);
let region =
self.infcx().next_region_var(
infer::Autoref(self.expr.span));
(ty::mk_rptr(tcx, region, self_mt),
ty::AutoDerefRef(ty::AutoDerefRef {
autoderefs: autoderefs+1,
autoref: Some(ty::AutoPtr(region, self_mt.mutbl))}))
}
ty::ty_evec(self_mt, vstore_slice(_)) => {
let region = self.infcx().next_region_var_nb(self.expr.span);
let region =
self.infcx().next_region_var(
infer::Autoref(self.expr.span));
(ty::mk_evec(tcx, self_mt, vstore_slice(region)),
ty::AutoDerefRef(ty::AutoDerefRef {
autoderefs: autoderefs,
@ -758,7 +762,9 @@ impl<'self> LookupContext<'self> {
-> Option<method_map_entry> {
// This is hokey. We should have mutability inference as a
// variable. But for now, try &const, then &, then &mut:
let region = self.infcx().next_region_var_nb(self.expr.span);
let region =
self.infcx().next_region_var(
infer::Autoref(self.expr.span));
for mutbls.iter().advance |mutbl| {
let autoref_ty = mk_autoref_ty(*mutbl, region);
match self.search_for_method(autoref_ty) {
@ -970,7 +976,8 @@ impl<'self> LookupContext<'self> {
let (_, opt_transformed_self_ty, fn_sig) =
replace_bound_regions_in_fn_sig(
tcx, @Nil, Some(transformed_self_ty), &bare_fn_ty.sig,
|_br| self.fcx.infcx().next_region_var_nb(self.expr.span));
|br| self.fcx.infcx().next_region_var(
infer::BoundRegionInFnCall(self.expr.span, br)));
let transformed_self_ty = opt_transformed_self_ty.get();
let fty = ty::mk_bare_fn(tcx, ty::BareFnTy {sig: fn_sig, ..bare_fn_ty});
debug!("after replacing bound regions, fty=%s", self.ty_to_str(fty));
@ -982,7 +989,7 @@ impl<'self> LookupContext<'self> {
// variables to unify etc). Since we checked beforehand, and
// nothing has changed in the meantime, this unification
// should never fail.
match self.fcx.mk_subty(false, self.self_expr.span,
match self.fcx.mk_subty(false, infer::Misc(self.self_expr.span),
rcvr_ty, transformed_self_ty) {
result::Ok(_) => (),
result::Err(_) => {

163
src/librustc/middle/typeck/check/mod.rs
View File

@ -467,8 +467,6 @@ pub fn check_fn(ccx: @mut CrateCtxt,
let pcx = pat_ctxt {
fcx: fcx,
map: pat_id_map(tcx.def_map, input.pat),
match_region: region,
block_region: region,
};
_match::check_pat(&pcx, input.pat, *arg_ty);
}
@ -686,9 +684,14 @@ impl FnCtxt {
result::Ok(self.block_region())
} else {
result::Err(RegionError {
msg: fmt!("named region `%s` not in scope here",
bound_region_ptr_to_str(self.tcx(), br)),
replacement: self.infcx().next_region_var_nb(span)
msg: {
fmt!("named region `%s` not in scope here",
bound_region_ptr_to_str(self.tcx(), br))
},
replacement: {
self.infcx().next_region_var(
infer::BoundRegionError(span))
}
})
}
}
@ -698,7 +701,7 @@ impl FnCtxt {
impl region_scope for FnCtxt {
fn anon_region(&self, span: span) -> Result<ty::Region, RegionError> {
result::Ok(self.infcx().next_region_var_nb(span))
result::Ok(self.infcx().next_region_var(infer::MiscVariable(span)))
}
fn self_region(&self, span: span) -> Result<ty::Region, RegionError> {
self.search_in_scope_regions(span, ty::br_self)
@ -845,11 +848,11 @@ impl FnCtxt {
pub fn mk_subty(&self,
a_is_expected: bool,
span: span,
origin: infer::TypeOrigin,
sub: ty::t,
sup: ty::t)
-> Result<(), ty::type_err> {
infer::mk_subty(self.infcx(), a_is_expected, span, sub, sup)
infer::mk_subty(self.infcx(), a_is_expected, origin, sub, sup)
}
pub fn can_mk_subty(&self, sub: ty::t, sup: ty::t)
@ -857,9 +860,16 @@ impl FnCtxt {
infer::can_mk_subty(self.infcx(), sub, sup)
}
pub fn mk_assignty(&self, expr: @ast::expr, sub: ty::t, sup: ty::t)
pub fn mk_assignty(&self,
expr: @ast::expr,
sub: ty::t,
sup: ty::t)
-> Result<(), ty::type_err> {
match infer::mk_coercety(self.infcx(), false, expr.span, sub, sup) {
match infer::mk_coercety(self.infcx(),
false,
infer::ExprAssignable(expr),
sub,
sup) {
Ok(None) => result::Ok(()),
Err(ref e) => result::Err((*e)),
Ok(Some(adjustment)) => {
@ -876,20 +886,19 @@ impl FnCtxt {
pub fn mk_eqty(&self,
a_is_expected: bool,
span: span,
origin: infer::TypeOrigin,
sub: ty::t,
sup: ty::t)
-> Result<(), ty::type_err> {
infer::mk_eqty(self.infcx(), a_is_expected, span, sub, sup)
infer::mk_eqty(self.infcx(), a_is_expected, origin, sub, sup)
}
pub fn mk_subr(&self,
a_is_expected: bool,
span: span,
origin: infer::SubregionOrigin,
sub: ty::Region,
sup: ty::Region)
-> Result<(), ty::type_err> {
infer::mk_subr(self.infcx(), a_is_expected, span, sub, sup)
sup: ty::Region) {
infer::mk_subr(self.infcx(), a_is_expected, origin, sub, sup)
}
pub fn with_region_lb<R>(@mut self, lb: ast::node_id, f: &fn() -> R)
@ -905,7 +914,9 @@ impl FnCtxt {
rp: Option<ty::region_variance>,
span: span)
-> Option<ty::Region> {
rp.map(|_rp| self.infcx().next_region_var_nb(span))
rp.map(
|_| self.infcx().next_region_var(
infer::BoundRegionInTypeOrImpl(span)))
}
pub fn type_error_message(&self,
@ -1089,7 +1100,8 @@ pub fn impl_self_ty(vcx: &VtableContext,
};
let self_r = if region_param.is_some() {
Some(vcx.infcx.next_region_var_nb(location_info.span))
Some(vcx.infcx.next_region_var(
infer::BoundRegionInTypeOrImpl(location_info.span)))
} else {
None
};
@ -1352,7 +1364,8 @@ pub fn check_expr_with_unifier(fcx: @mut FnCtxt,
let (_, _, fn_sig) =
replace_bound_regions_in_fn_sig(
fcx.tcx(), @Nil, None, &fn_sig,
|_br| fcx.infcx().next_region_var_nb(call_expr.span));
|br| fcx.infcx().next_region_var(
infer::BoundRegionInFnCall(call_expr.span, br)));
// Call the generic checker.
check_argument_types(fcx, call_expr.span, fn_sig.inputs, f,
@ -1423,27 +1436,42 @@ pub fn check_expr_with_unifier(fcx: @mut FnCtxt,
// A generic function for checking the then and else in an if
// or if-check
fn check_then_else(fcx: @mut FnCtxt,
thn: &ast::blk,
elsopt: Option<@ast::expr>,
cond_expr: @ast::expr,
then_blk: &ast::blk,
opt_else_expr: Option<@ast::expr>,
id: ast::node_id,
_sp: span) {
let if_t =
match elsopt {
Some(els) => {
let if_t = fcx.infcx().next_ty_var();
check_block(fcx, thn);
let thn_t = fcx.node_ty(thn.node.id);
demand::suptype(fcx, thn.span, if_t, thn_t);
check_expr_has_type(fcx, els, if_t);
if_t
}
None => {
check_block_no_value(fcx, thn);
ty::mk_nil()
}
};
sp: span,
expected: Option<ty::t>) {
check_expr_has_type(fcx, cond_expr, ty::mk_bool());
fcx.write_ty(id, if_t);
let branches_ty = match opt_else_expr {
Some(else_expr) => {
check_block_with_expected(fcx, then_blk, expected);
let then_ty = fcx.node_ty(then_blk.node.id);
check_expr_with_opt_hint(fcx, else_expr, expected);
let else_ty = fcx.expr_ty(else_expr);
infer::common_supertype(fcx.infcx(),
infer::IfExpression(sp),
true,
then_ty,
else_ty)
}
None => {
check_block_no_value(fcx, then_blk);
ty::mk_nil()
}
};
let cond_ty = fcx.expr_ty(cond_expr);
let if_ty = if ty::type_is_error(cond_ty) {
ty::mk_err()
} else if ty::type_is_bot(cond_ty) {
ty::mk_bot()
} else {
branches_ty
};
fcx.write_ty(id, if_ty);
}
fn lookup_op_method(fcx: @mut FnCtxt,
@ -2085,7 +2113,7 @@ pub fn check_expr_with_unifier(fcx: @mut FnCtxt,
let expected_sty = unpack_expected(fcx, expected, |x| Some(copy *x));
let inner_ty = match expected_sty {
Some(ty::ty_closure(ref fty)) => {
match fcx.mk_subty(false, expr.span,
match fcx.mk_subty(false, infer::Misc(expr.span),
fty.sig.output, ty::mk_bool()) {
result::Ok(_) => {
ty::mk_closure(tcx, ty::ClosureTy {
@ -2395,7 +2423,8 @@ pub fn check_expr_with_unifier(fcx: @mut FnCtxt,
// Finally, borrowck is charged with guaranteeing that the
// value whose address was taken can actually be made to live
// as long as it needs to live.
let region = fcx.infcx().next_region_var_nb(expr.span);
let region = fcx.infcx().next_region_var(
infer::AddrOfRegion(expr.span));
let tm = ty::mt { ty: fcx.expr_ty(oprnd), mutbl: mutbl };
let oprnd_t = if ty::type_is_error(tm.ty) {
@ -2437,7 +2466,7 @@ pub fn check_expr_with_unifier(fcx: @mut FnCtxt,
Some(t) => t, None => fcx.ret_ty
};
match expr_opt {
None => match fcx.mk_eqty(false, expr.span,
None => match fcx.mk_eqty(false, infer::Misc(expr.span),
ret_ty, ty::mk_nil()) {
result::Ok(_) => { /* fall through */ }
result::Err(_) => {
@ -2487,25 +2516,9 @@ pub fn check_expr_with_unifier(fcx: @mut FnCtxt,
fcx.write_nil(id);
}
}
ast::expr_if(cond, ref thn, elsopt) => {
check_expr_has_type(fcx, cond, ty::mk_bool());
check_then_else(fcx, thn, elsopt, id, expr.span);
let cond_ty = fcx.expr_ty(cond);
let then_ty = fcx.node_ty(thn.node.id);
let else_is_bot = elsopt.map_default(false, |els| {
ty::type_is_bot(fcx.expr_ty(*els))});
if ty::type_is_error(cond_ty) || ty::type_is_error(then_ty) {
fcx.write_error(id);
}
else if elsopt.map_default(false, |els| {
ty::type_is_error(fcx.expr_ty(*els)) }) {
fcx.write_error(id);
}
else if ty::type_is_bot(cond_ty) ||
(ty::type_is_bot(then_ty) && else_is_bot) {
fcx.write_bot(id);
}
// Other cases were handled by check_then_else
ast::expr_if(cond, ref then_blk, opt_else_expr) => {
check_then_else(fcx, cond, then_blk, opt_else_expr,
id, expr.span, expected);
}
ast::expr_while(cond, ref body) => {
check_expr_has_type(fcx, cond, ty::mk_bool());
@ -2533,30 +2546,6 @@ pub fn check_expr_with_unifier(fcx: @mut FnCtxt,
}
ast::expr_match(discrim, ref arms) => {
_match::check_match(fcx, expr, discrim, *arms);
let discrim_ty = fcx.expr_ty(discrim);
let arm_tys = arms.map(|a| fcx.node_ty(a.body.node.id));
if ty::type_is_error(discrim_ty) ||
arm_tys.iter().any_(|t| ty::type_is_error(*t)) {
fcx.write_error(id);
}
// keep in mind that `all` returns true in the empty vec case,
// which is what we want
else if ty::type_is_bot(discrim_ty) ||
arm_tys.iter().all(|t| ty::type_is_bot(*t)) {
fcx.write_bot(id);
}
else {
// Find the first non-_|_ arm.
// We know there's at least one because we already checked
// for n=0 as well as all arms being _|_ in the previous
// `if`.
for arm_tys.iter().advance |arm_ty| {
if !ty::type_is_bot(*arm_ty) {
fcx.write_ty(id, *arm_ty);
break;
}
}
}
}
ast::expr_fn_block(ref decl, ref body) => {
check_expr_fn(fcx, expr, None,
@ -2686,7 +2675,7 @@ pub fn check_expr_with_unifier(fcx: @mut FnCtxt,
let el = ty::sequence_element_type(fcx.tcx(),
t1);
infer::mk_eqty(fcx.infcx(), false,
sp, el, t2).is_ok()
infer::Misc(sp), el, t2).is_ok()
}
}
@ -2907,8 +2896,6 @@ pub fn check_decl_local(fcx: @mut FnCtxt, local: @ast::local) {
let pcx = pat_ctxt {
fcx: fcx,
map: pat_id_map(tcx.def_map, local.node.pat),
match_region: region,
block_region: region,
};
_match::check_pat(&pcx, local.node.pat, t);
let pat_ty = fcx.node_ty(local.node.pat.id);
@ -3412,7 +3399,7 @@ pub fn ast_expr_vstore_to_vstore(fcx: @mut FnCtxt,
ast::expr_vstore_uniq => ty::vstore_uniq,
ast::expr_vstore_box | ast::expr_vstore_mut_box => ty::vstore_box,
ast::expr_vstore_slice | ast::expr_vstore_mut_slice => {
let r = fcx.infcx().next_region_var_nb(e.span);
let r = fcx.infcx().next_region_var(infer::AddrOfSlice(e.span));
ty::vstore_slice(r)
}
}

182
src/librustc/middle/typeck/check/regionck.rs
View File

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
/*
/*!
The region check is a final pass that runs over the AST after we have
inferred the type constraints but before we have actually finalized
@ -35,7 +35,9 @@ use middle::typeck::check::FnCtxt;
use middle::typeck::check::regionmanip::relate_nested_regions;
use middle::typeck::infer::resolve_and_force_all_but_regions;
use middle::typeck::infer::resolve_type;
use util::ppaux::{note_and_explain_region, ty_to_str, region_to_str};
use middle::typeck::infer;
use util::ppaux::{note_and_explain_region, ty_to_str,
region_to_str};
use middle::pat_util;
use std::result;
@ -224,7 +226,9 @@ fn constrain_bindings_in_pat(pat: @ast::pat, rcx: @mut Rcx) {
// variable's type enclose at least the variable's scope.
let encl_region = tcx.region_maps.encl_region(id);
constrain_regions_in_type_of_node(rcx, id, encl_region, span);
constrain_regions_in_type_of_node(
rcx, id, encl_region,
infer::BindingTypeIsNotValidAtDecl(span));
}
}
@ -298,7 +302,8 @@ fn visit_expr(expr: @ast::expr, (rcx, v): (@mut Rcx, rvt)) {
//
// FIXME(#6268) remove to support nested method calls
constrain_regions_in_type_of_node(
rcx, expr.id, ty::re_scope(expr.id), expr.span);
rcx, expr.id, ty::re_scope(expr.id),
infer::AutoBorrow(expr.span));
}
}
_ => {}
@ -361,8 +366,11 @@ fn visit_expr(expr: @ast::expr, (rcx, v): (@mut Rcx, rvt)) {
match ty::get(target_ty).sty {
ty::ty_trait(_, _, ty::RegionTraitStore(trait_region), _, _) => {
let source_ty = rcx.fcx.expr_ty(source);
constrain_regions_in_type(rcx, trait_region,
expr.span, source_ty);
constrain_regions_in_type(
rcx,
trait_region,
infer::RelateObjectBound(expr.span),
source_ty);
}
_ => ()
}
@ -379,7 +387,8 @@ fn visit_expr(expr: @ast::expr, (rcx, v): (@mut Rcx, rvt)) {
//
// FIXME(#6268) nested method calls requires that this rule change
let ty0 = rcx.resolve_node_type(expr.id);
constrain_regions_in_type(rcx, ty::re_scope(expr.id), expr.span, ty0);
constrain_regions_in_type(rcx, ty::re_scope(expr.id),
infer::AddrOf(expr.span), ty0);
}
ast::expr_match(discr, ref arms) => {
@ -418,20 +427,8 @@ fn constrain_callee(rcx: @mut Rcx,
match ty::get(callee_ty).sty {
ty::ty_bare_fn(*) => { }
ty::ty_closure(ref closure_ty) => {
match rcx.fcx.mk_subr(true, callee_expr.span,
call_region, closure_ty.region) {
result::Err(_) => {
tcx.sess.span_err(
callee_expr.span,
fmt!("cannot invoke closure outside of its lifetime"));
note_and_explain_region(
tcx,
"the closure is only valid for ",
closure_ty.region,
"");
}
result::Ok(_) => {}
}
rcx.fcx.mk_subr(true, infer::InvokeClosure(callee_expr.span),
call_region, closure_ty.region);
}
_ => {
// this should not happen, but it does if the program is
@ -479,7 +476,8 @@ fn constrain_call(rcx: @mut Rcx,
// ensure that any regions appearing in the argument type are
// valid for at least the lifetime of the function:
constrain_regions_in_type_of_node(
rcx, arg_expr.id, callee_region, arg_expr.span);
rcx, arg_expr.id, callee_region,
infer::CallArg(arg_expr.span));
// unfortunately, there are two means of taking implicit
// references, and we need to propagate constraints as a
@ -493,7 +491,7 @@ fn constrain_call(rcx: @mut Rcx,
// as loop above, but for receiver
for receiver.iter().advance |&r| {
constrain_regions_in_type_of_node(
rcx, r.id, callee_region, r.span);
rcx, r.id, callee_region, infer::CallRcvr(r.span));
if implicitly_ref_args {
guarantor::for_by_ref(rcx, r, callee_scope);
}
@ -502,7 +500,8 @@ fn constrain_call(rcx: @mut Rcx,
// constrain regions that may appear in the return type to be
// valid for the function call:
constrain_regions_in_type(
rcx, callee_region, call_expr.span, fn_sig.output);
rcx, callee_region, infer::CallReturn(call_expr.span),
fn_sig.output);
}
fn constrain_derefs(rcx: @mut Rcx,
@ -545,20 +544,8 @@ pub fn mk_subregion_due_to_derefence(rcx: @mut Rcx,
deref_span: span,
minimum_lifetime: ty::Region,
maximum_lifetime: ty::Region) {
match rcx.fcx.mk_subr(true, deref_span,
minimum_lifetime, maximum_lifetime) {
result::Ok(*) => {}
result::Err(*) => {
rcx.tcx().sess.span_err(
deref_span,
fmt!("dereference of reference outside its lifetime"));
note_and_explain_region(
rcx.tcx(),
"the reference is only valid for ",
maximum_lifetime,
"");
}
}
rcx.fcx.mk_subr(true, infer::DerefPointer(deref_span),
minimum_lifetime, maximum_lifetime)
}
@ -581,19 +568,8 @@ fn constrain_index(rcx: @mut Rcx,
match ty::get(indexed_ty).sty {
ty::ty_estr(ty::vstore_slice(r_ptr)) |
ty::ty_evec(_, ty::vstore_slice(r_ptr)) => {
match rcx.fcx.mk_subr(true, index_expr.span, r_index_expr, r_ptr) {
result::Ok(*) => {}
result::Err(*) => {
tcx.sess.span_err(
index_expr.span,
fmt!("index of slice outside its lifetime"));
note_and_explain_region(
tcx,
"the slice is only valid for ",
r_ptr,
"");
}
}
rcx.fcx.mk_subr(true, infer::IndexSlice(index_expr.span),
r_index_expr, r_ptr);
}
_ => {}
@ -616,25 +592,8 @@ fn constrain_free_variables(rcx: @mut Rcx,
let def = freevar.def;
let en_region = encl_region_of_def(rcx.fcx, def);
debug!("en_region = %s", en_region.repr(tcx));
match rcx.fcx.mk_subr(true, freevar.span,
region, en_region) {
result::Ok(()) => {}
result::Err(_) => {
tcx.sess.span_err(
freevar.span,
"captured variable does not outlive the enclosing closure");
note_and_explain_region(
tcx,
"captured variable is valid for ",
en_region,
"");
note_and_explain_region(
tcx,
"closure is valid for ",
region,
"");
}
}
rcx.fcx.mk_subr(true, infer::FreeVariable(freevar.span),
region, en_region);
}
}
@ -642,7 +601,7 @@ fn constrain_regions_in_type_of_node(
rcx: @mut Rcx,
id: ast::node_id,
minimum_lifetime: ty::Region,
span: span) -> bool
origin: infer::SubregionOrigin) -> bool
{
//! Guarantees that any lifetimes which appear in the type of
//! the node `id` (after applying adjustments) are valid for at
@ -655,18 +614,18 @@ fn constrain_regions_in_type_of_node(
// report errors later on in the writeback phase.
let ty0 = rcx.resolve_node_type(id);
let adjustment = rcx.fcx.inh.adjustments.find_copy(&id);
let ty = ty::adjust_ty(tcx, span, ty0, adjustment);
let ty = ty::adjust_ty(tcx, origin.span(), ty0, adjustment);
debug!("constrain_regions_in_type_of_node(\
ty=%s, ty0=%s, id=%d, minimum_lifetime=%?, adjustment=%?)",
ty_to_str(tcx, ty), ty_to_str(tcx, ty0),
id, minimum_lifetime, adjustment);
constrain_regions_in_type(rcx, minimum_lifetime, span, ty)
constrain_regions_in_type(rcx, minimum_lifetime, origin, ty)
}
fn constrain_regions_in_type(
rcx: @mut Rcx,
minimum_lifetime: ty::Region,
span: span,
origin: infer::SubregionOrigin,
ty: ty::t) -> bool
{
/*!
@ -700,40 +659,14 @@ fn constrain_regions_in_type(
// (e.g., the `&` in `fn(&T)`). Such regions need not be
// constrained by `minimum_lifetime` as they are placeholders
// for regions that are as-yet-unknown.
} else if r_sub == minimum_lifetime {
rcx.fcx.mk_subr(
true, origin,
r_sub, r_sup);
} else {
match rcx.fcx.mk_subr(true, span, r_sub, r_sup) {
result::Err(_) => {
if r_sub == minimum_lifetime {
tcx.sess.span_err(
span,
fmt!("reference is not valid outside of its lifetime"));
note_and_explain_region(
tcx,
"the reference is only valid for ",
r_sup,
"");
} else {
tcx.sess.span_err(
span,
fmt!("in type `%s`, pointer has a longer lifetime than \
the data it references",
rcx.fcx.infcx().ty_to_str(ty)));
note_and_explain_region(
tcx,
"the pointer is valid for ",
r_sub,
"");
note_and_explain_region(
tcx,
"but the referenced data is only valid for ",
r_sup,
"");
}
rcx.errors_reported += 1u;
}
result::Ok(()) => {
}
}
rcx.fcx.mk_subr(
true, infer::ReferenceOutlivesReferent(ty, origin.span()),
r_sub, r_sup);
}
}
@ -788,8 +721,9 @@ pub mod guarantor {
*/
use middle::typeck::check::regionck::{Rcx, infallibly_mk_subr};
use middle::typeck::check::regionck::Rcx;
use middle::typeck::check::regionck::mk_subregion_due_to_derefence;
use middle::typeck::infer;
use middle::ty;
use syntax::ast;
use syntax::codemap::span;
@ -869,9 +803,11 @@ pub mod guarantor {
rcx: @mut Rcx,
expr: @ast::expr,
sub_region: ty::Region,
sup_region: Option<ty::Region>) {
sup_region: Option<ty::Region>)
{
for sup_region.iter().advance |r| {
infallibly_mk_subr(rcx, true, expr.span, sub_region, *r);
rcx.fcx.mk_subr(true, infer::Reborrow(expr.span),
sub_region, *r);
}
}
}
@ -929,7 +865,7 @@ pub mod guarantor {
let tcx = rcx.fcx.ccx.tcx;
debug!("rptr_ty=%s", ty_to_str(tcx, rptr_ty));
let r = ty::ty_region(tcx, span, rptr_ty);
infallibly_mk_subr(rcx, true, span, r, bound);
rcx.fcx.mk_subr(true, infer::Reborrow(span), r, bound);
}
}
@ -1259,27 +1195,3 @@ pub mod guarantor {
}
}
pub fn infallibly_mk_subr(rcx: @mut Rcx,
a_is_expected: bool,
span: span,
a: ty::Region,
b: ty::Region) {
/*!
* Constrains `a` to be a subregion of `b`. In many cases, we
* know that this can never yield an error due to the way that
* region inferencing works. Therefore just report a bug if we
* ever see `Err(_)`.
*/
match rcx.fcx.mk_subr(a_is_expected, span, a, b) {
result::Ok(()) => {}
result::Err(e) => {
rcx.fcx.ccx.tcx.sess.span_bug(
span,
fmt!("Supposedly infallible attempt to \
make %? < %? failed: %?",
a, b, e));
}
}
}

40
src/librustc/middle/typeck/check/vtable.rs
View File

@ -101,18 +101,18 @@ fn lookup_vtables(vcx: &VtableContext,
// Substitute the values of the type parameters that may
// appear in the bound.
let trait_ref = (*trait_ref).subst(tcx, substs);
let trait_ref = trait_ref.subst(tcx, substs);
debug!("after subst: %s", trait_ref.repr(tcx));
match lookup_vtable(vcx, location_info, *ty, &trait_ref, is_early) {
match lookup_vtable(vcx, location_info, *ty, trait_ref, is_early) {
Some(vtable) => param_result.push(vtable),
None => {
vcx.tcx().sess.span_fatal(
location_info.span,
fmt!("failed to find an implementation of \
trait %s for %s",
vcx.infcx.trait_ref_to_str(&trait_ref),
vcx.infcx.trait_ref_to_str(trait_ref),
vcx.infcx.ty_to_str(*ty)));
}
}
@ -152,8 +152,8 @@ fn fixup_substs(vcx: &VtableContext, location_info: &LocationInfo,
fn relate_trait_refs(vcx: &VtableContext,
location_info: &LocationInfo,
act_trait_ref: &ty::TraitRef,
exp_trait_ref: &ty::TraitRef)
act_trait_ref: @ty::TraitRef,
exp_trait_ref: @ty::TraitRef)
{
/*!
*
@ -162,8 +162,11 @@ fn relate_trait_refs(vcx: &VtableContext,
* error otherwise.
*/
match infer::mk_sub_trait_refs(vcx.infcx, false, location_info.span,
act_trait_ref, exp_trait_ref)
match infer::mk_sub_trait_refs(vcx.infcx,
false,
infer::RelateTraitRefs(location_info.span),
act_trait_ref,
exp_trait_ref)
{
result::Ok(()) => {} // Ok.
result::Err(ref err) => {
@ -191,7 +194,7 @@ fn relate_trait_refs(vcx: &VtableContext,
fn lookup_vtable(vcx: &VtableContext,
location_info: &LocationInfo,
ty: ty::t,
trait_ref: &ty::TraitRef,
trait_ref: @ty::TraitRef,
is_early: bool)
-> Option<vtable_origin>
{
@ -304,7 +307,8 @@ fn lookup_vtable(vcx: &VtableContext,
} = impl_self_ty(vcx, location_info, im.did);
match infer::mk_subty(vcx.infcx,
false,
location_info.span,
infer::RelateSelfType(
location_info.span),
ty,
for_ty) {
result::Err(_) => loop,
@ -337,11 +341,10 @@ fn lookup_vtable(vcx: &VtableContext,
vcx.infcx.trait_ref_to_str(trait_ref),
vcx.infcx.trait_ref_to_str(of_trait_ref));
let of_trait_ref =
(*of_trait_ref).subst(tcx, &substs);
let of_trait_ref = of_trait_ref.subst(tcx, &substs);
relate_trait_refs(
vcx, location_info,
&of_trait_ref, trait_ref);
of_trait_ref, trait_ref);
// Recall that trait_ref -- the trait type
// we're casting to -- is the trait with
@ -450,7 +453,7 @@ fn fixup_ty(vcx: &VtableContext,
fn connect_trait_tps(vcx: &VtableContext,
location_info: &LocationInfo,
impl_substs: &ty::substs,
trait_ref: &ty::TraitRef,
trait_ref: @ty::TraitRef,
impl_did: ast::def_id)
{
let tcx = vcx.tcx();
@ -461,8 +464,8 @@ fn connect_trait_tps(vcx: &VtableContext,
"connect_trait_tps invoked on a type impl")
};
let impl_trait_ref = (*impl_trait_ref).subst(tcx, impl_substs);
relate_trait_refs(vcx, location_info, &impl_trait_ref, trait_ref);
let impl_trait_ref = impl_trait_ref.subst(tcx, impl_substs);
relate_trait_refs(vcx, location_info, impl_trait_ref, trait_ref);
}
fn insert_vtables(fcx: @mut FnCtxt,
@ -581,7 +584,7 @@ pub fn early_resolve_expr(ex: @ast::expr,
ccx: fcx.ccx,
infcx: fcx.infcx()
};
let target_trait_ref = ty::TraitRef {
let target_trait_ref = @ty::TraitRef {
def_id: target_def_id,
substs: ty::substs {
tps: copy target_substs.tps,
@ -593,7 +596,7 @@ pub fn early_resolve_expr(ex: @ast::expr,
lookup_vtable(&vcx,
location_info,
mt.ty,
&target_trait_ref,
target_trait_ref,
is_early);
match vtable_opt {
Some(vtable) => {
@ -622,7 +625,8 @@ pub fn early_resolve_expr(ex: @ast::expr,
ty::RegionTraitStore(rb)) => {
infer::mk_subr(fcx.infcx(),
false,
ex.span,
infer::RelateObjectBound(
ex.span),
rb,
ra);
}

26
src/librustc/middle/typeck/coherence.rs
View File

@ -36,6 +36,7 @@ use middle::typeck::infer::combine::Combine;
use middle::typeck::infer::InferCtxt;
use middle::typeck::infer::{new_infer_ctxt, resolve_ivar};
use middle::typeck::infer::{resolve_nested_tvar, resolve_type};
use middle::typeck::infer;
use syntax::ast::{crate, def_id, def_struct, def_ty};
use syntax::ast::{item, item_enum, item_impl, item_mod, item_struct};
use syntax::ast::{local_crate, method, trait_ref, ty_path};
@ -546,10 +547,10 @@ impl CoherenceChecker {
pub fn universally_quantify_polytype(&self,
polytype: ty_param_bounds_and_ty)
-> UniversalQuantificationResult {
// NDM--this span is bogus.
let self_region =
polytype.generics.region_param.map(
|_r| self.inference_context.next_region_var_nb(dummy_sp()));
|_| self.inference_context.next_region_var(
infer::BoundRegionInCoherence));
let bounds_count = polytype.generics.type_param_defs.len();
let type_parameters = self.inference_context.next_ty_vars(bounds_count);
@ -580,11 +581,9 @@ impl CoherenceChecker {
b: &'a
UniversalQuantificationResult)
-> bool {
let mut might_unify = true;
let _ = do self.inference_context.probe {
let result = self.inference_context.sub(true, dummy_sp())
.tys(a.monotype, b.monotype);
if result.is_ok() {
match infer::can_mk_subty(self.inference_context,
a.monotype, b.monotype) {
Ok(_) => {
// Check to ensure that each parameter binding respected its
// kind bounds.
let xs = [a, b];
@ -604,8 +603,7 @@ impl CoherenceChecker {
self.inference_context.tcx,
resolved_ty)
{
might_unify = false;
break;
return false;
}
}
Err(*) => {
@ -615,13 +613,13 @@ impl CoherenceChecker {
}
}
}
} else {
might_unify = false;
true
}
result
};
might_unify
Err(_) => {
false
}
}
}
pub fn get_self_type_for_implementation(&self, implementation: @Impl)

3
src/librustc/middle/typeck/collect.rs
View File

@ -615,7 +615,8 @@ pub fn compare_impl_method(tcx: ty::ctxt,
};
debug!("trait_fty (post-subst): %s", trait_fty.repr(tcx));
match infer::mk_subty(infcx, false, cm.span, impl_fty, trait_fty) {
match infer::mk_subty(infcx, false, infer::MethodCompatCheck(cm.span),
impl_fty, trait_fty) {
result::Ok(()) => {}
result::Err(ref terr) => {
tcx.sess.span_err(

12
src/librustc/middle/typeck/infer/coercion.rs
View File

@ -70,7 +70,7 @@ use middle::ty::{AutoDerefRef};
use middle::ty::{vstore_slice, vstore_box, vstore_uniq};
use middle::ty::{mt};
use middle::ty;
use middle::typeck::infer::{CoerceResult, resolve_type};
use middle::typeck::infer::{CoerceResult, resolve_type, Coercion};
use middle::typeck::infer::combine::CombineFields;
use middle::typeck::infer::sub::Sub;
use middle::typeck::infer::to_str::InferStr;
@ -165,7 +165,7 @@ impl Coerce {
}
Err(e) => {
self.infcx.tcx.sess.span_bug(
self.span,
self.trace.origin.span(),
fmt!("Failed to resolve even without \
any force options: %?", e));
}
@ -189,7 +189,7 @@ impl Coerce {
// yield.
let sub = Sub(**self);
let r_borrow = self.infcx.next_region_var_nb(self.span);
let r_borrow = self.infcx.next_region_var(Coercion(self.trace));
let inner_ty = match *sty_a {
ty::ty_box(mt_a) => mt_a.ty,
@ -227,7 +227,7 @@ impl Coerce {
}
};
let r_a = self.infcx.next_region_var_nb(self.span);
let r_a = self.infcx.next_region_var(Coercion(self.trace));
let a_borrowed = ty::mk_estr(self.infcx.tcx, vstore_slice(r_a));
if_ok!(self.subtype(a_borrowed, b));
Ok(Some(@AutoDerefRef(AutoDerefRef {
@ -247,7 +247,7 @@ impl Coerce {
b.inf_str(self.infcx));
let sub = Sub(**self);
let r_borrow = self.infcx.next_region_var_nb(self.span);
let r_borrow = self.infcx.next_region_var(Coercion(self.trace));
let ty_inner = match *sty_a {
ty::ty_evec(mt, _) => mt.ty,
_ => {
@ -285,7 +285,7 @@ impl Coerce {
}
};
let r_borrow = self.infcx.next_region_var_nb(self.span);
let r_borrow = self.infcx.next_region_var(Coercion(self.trace));
let a_borrowed = ty::mk_closure(
self.infcx.tcx,
ty::ClosureTy {

5
src/librustc/middle/typeck/infer/combine.rs
View File

@ -65,6 +65,7 @@ use middle::typeck::infer::sub::Sub;
use middle::typeck::infer::to_str::InferStr;
use middle::typeck::infer::unify::{InferCtxtMethods};
use middle::typeck::infer::{InferCtxt, cres, ures};
use middle::typeck::infer::{TypeOrigin, TypeTrace};
use util::common::indent;
use std::result::{iter_vec2, map_vec2};
@ -79,7 +80,7 @@ pub trait Combine {
fn infcx(&self) -> @mut InferCtxt;
fn tag(&self) -> ~str;
fn a_is_expected(&self) -> bool;
fn span(&self) -> span;
fn trace(&self) -> TypeTrace;
fn sub(&self) -> Sub;
fn lub(&self) -> Lub;
@ -121,7 +122,7 @@ pub trait Combine {
pub struct CombineFields {
infcx: @mut InferCtxt,
a_is_expected: bool,
span: span,
trace: TypeTrace,
}
pub fn expected_found<C:Combine,T>(

243
src/librustc/middle/typeck/infer/doc.rs Normal file
View File

@ -0,0 +1,243 @@
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
/*!
# Type inference engine
This is loosely based on standard HM-type inference, but with an
extension to try and accommodate subtyping. There is nothing
principled about this extension; it's sound---I hope!---but it's a
heuristic, ultimately, and does not guarantee that it finds a valid
typing even if one exists (in fact, there are known scenarios where it
fails, some of which may eventually become problematic).
## Key idea
The main change is that each type variable T is associated with a
lower-bound L and an upper-bound U. L and U begin as bottom and top,
respectively, but gradually narrow in response to new constraints
being introduced. When a variable is finally resolved to a concrete
type, it can (theoretically) select any type that is a supertype of L
and a subtype of U.
There are several critical invariants which we maintain:
- the upper-bound of a variable only becomes lower and the lower-bound
only becomes higher over time;
- the lower-bound L is always a subtype of the upper bound U;
- the lower-bound L and upper-bound U never refer to other type variables,
but only to types (though those types may contain type variables).
> An aside: if the terms upper- and lower-bound confuse you, think of
> "supertype" and "subtype". The upper-bound is a "supertype"
> (super=upper in Latin, or something like that anyway) and the lower-bound
> is a "subtype" (sub=lower in Latin). I find it helps to visualize
> a simple class hierarchy, like Java minus interfaces and
> primitive types. The class Object is at the root (top) and other
> types lie in between. The bottom type is then the Null type.
> So the tree looks like:
>
> Object
> / \
> String Other
> \ /
> (null)
>
> So the upper bound type is the "supertype" and the lower bound is the
> "subtype" (also, super and sub mean upper and lower in Latin, or something
> like that anyway).
## Satisfying constraints
At a primitive level, there is only one form of constraint that the
inference understands: a subtype relation. So the outside world can
say "make type A a subtype of type B". If there are variables
involved, the inferencer will adjust their upper- and lower-bounds as
needed to ensure that this relation is satisfied. (We also allow "make
type A equal to type B", but this is translated into "A <: B" and "B
<: A")
As stated above, we always maintain the invariant that type bounds
never refer to other variables. This keeps the inference relatively
simple, avoiding the scenario of having a kind of graph where we have
to pump constraints along and reach a fixed point, but it does impose
some heuristics in the case where the user is relating two type
variables A <: B.
Combining two variables such that variable A will forever be a subtype
of variable B is the trickiest part of the algorithm because there is
often no right choice---that is, the right choice will depend on
future constraints which we do not yet know. The problem comes about
because both A and B have bounds that can be adjusted in the future.
Let's look at some of the cases that can come up.
Imagine, to start, the best case, where both A and B have an upper and
lower bound (that is, the bounds are not top nor bot respectively). In
that case, if we're lucky, A.ub <: B.lb, and so we know that whatever
A and B should become, they will forever have the desired subtyping
relation. We can just leave things as they are.
### Option 1: Unify
However, suppose that A.ub is *not* a subtype of B.lb. In
that case, we must make a decision. One option is to unify A
and B so that they are one variable whose bounds are:
UB = GLB(A.ub, B.ub)
LB = LUB(A.lb, B.lb)
(Note that we will have to verify that LB <: UB; if it does not, the
types are not intersecting and there is an error) In that case, A <: B
holds trivially because A==B. However, we have now lost some
flexibility, because perhaps the user intended for A and B to end up
as different types and not the same type.
Pictorally, what this does is to take two distinct variables with
(hopefully not completely) distinct type ranges and produce one with
the intersection.
B.ub B.ub
/\ /
A.ub / \ A.ub /
/ \ / \ \ /
/ X \ UB
/ / \ \ / \
/ / / \ / /
\ \ / / \ /
\ X / LB
\ / \ / / \
\ / \ / / \
A.lb B.lb A.lb B.lb
### Option 2: Relate UB/LB
Another option is to keep A and B as distinct variables but set their
bounds in such a way that, whatever happens, we know that A <: B will hold.
This can be achieved by ensuring that A.ub <: B.lb. In practice there
are two ways to do that, depicted pictorally here:
Before Option #1 Option #2
B.ub B.ub B.ub
/\ / \ / \
A.ub / \ A.ub /(B')\ A.ub /(B')\
/ \ / \ \ / / \ / /
/ X \ __UB____/ UB /
/ / \ \ / | | /
/ / / \ / | | /
\ \ / / /(A')| | /
\ X / / LB ______LB/
\ / \ / / / \ / (A')/ \
\ / \ / \ / \ \ / \
A.lb B.lb A.lb B.lb A.lb B.lb
In these diagrams, UB and LB are defined as before. As you can see,
the new ranges `A'` and `B'` are quite different from the range that
would be produced by unifying the variables.
### What we do now
Our current technique is to *try* (transactionally) to relate the
existing bounds of A and B, if there are any (i.e., if `UB(A) != top
&& LB(B) != bot`). If that succeeds, we're done. If it fails, then
we merge A and B into same variable.
This is not clearly the correct course. For example, if `UB(A) !=
top` but `LB(B) == bot`, we could conceivably set `LB(B)` to `UB(A)`
and leave the variables unmerged. This is sometimes the better
course, it depends on the program.
The main case which fails today that I would like to support is:
fn foo<T>(x: T, y: T) { ... }
fn bar() {
let x: @mut int = @mut 3;
let y: @int = @3;
foo(x, y);
}
In principle, the inferencer ought to find that the parameter `T` to
`foo(x, y)` is `@const int`. Today, however, it does not; this is
because the type variable `T` is merged with the type variable for
`X`, and thus inherits its UB/LB of `@mut int`. This leaves no
flexibility for `T` to later adjust to accommodate `@int`.
### What to do when not all bounds are present
In the prior discussion we assumed that A.ub was not top and B.lb was
not bot. Unfortunately this is rarely the case. Often type variables
have "lopsided" bounds. For example, if a variable in the program has
been initialized but has not been used, then its corresponding type
variable will have a lower bound but no upper bound. When that
variable is then used, we would like to know its upper bound---but we
don't have one! In this case we'll do different things depending on
how the variable is being used.
## Transactional support
Whenever we adjust merge variables or adjust their bounds, we always
keep a record of the old value. This allows the changes to be undone.
## Regions
I've only talked about type variables here, but region variables
follow the same principle. They have upper- and lower-bounds. A
region A is a subregion of a region B if A being valid implies that B
is valid. This basically corresponds to the block nesting structure:
the regions for outer block scopes are superregions of those for inner
block scopes.
## Integral and floating-point type variables
There is a third variety of type variable that we use only for
inferring the types of unsuffixed integer literals. Integral type
variables differ from general-purpose type variables in that there's
no subtyping relationship among the various integral types, so instead
of associating each variable with an upper and lower bound, we just
use simple unification. Each integer variable is associated with at
most one integer type. Floating point types are handled similarly to
integral types.
## GLB/LUB
Computing the greatest-lower-bound and least-upper-bound of two
types/regions is generally straightforward except when type variables
are involved. In that case, we follow a similar "try to use the bounds
when possible but otherwise merge the variables" strategy. In other
words, `GLB(A, B)` where `A` and `B` are variables will often result
in `A` and `B` being merged and the result being `A`.
## Type coercion
We have a notion of assignability which differs somewhat from
subtyping; in particular it may cause region borrowing to occur. See
the big comment later in this file on Type Coercion for specifics.
### In conclusion
I showed you three ways to relate `A` and `B`. There are also more,
of course, though I'm not sure if there are any more sensible options.
The main point is that there are various options, each of which
produce a distinct range of types for `A` and `B`. Depending on what
the correct values for A and B are, one of these options will be the
right choice: but of course we don't know the right values for A and B
yet, that's what we're trying to find! In our code, we opt to unify
(Option #1).
# Implementation details
We make use of a trait-like impementation strategy to consolidate
duplicated code between subtypes, GLB, and LUB computations. See the
section on "Type Combining" below for details.
*/

472
src/librustc/middle/typeck/infer/error_reporting.rs Normal file
View File

@ -0,0 +1,472 @@
// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
/*!
Error Reporting Code for the inference engine
Because of the way inference, and in particular region inference,
works, it often happens that errors are not detected until far after
the relevant line of code has been type-checked. Therefore, there is
an elaborate system to track why a particular constraint in the
inference graph arose so that we can explain to the user what gave
rise to a patricular error.
The basis of the system are the "origin" types. An "origin" is the
reason that a constraint or inference variable arose. There are
different "origin" enums for different kinds of constraints/variables
(e.g., `TypeOrigin`, `RegionVariableOrigin`). An origin always has
a span, but also more information so that we can generate a meaningful
error message.
Having a catalogue of all the different reasons an error can arise is
also useful for other reasons, like cross-referencing FAQs etc, though
we are not really taking advantage of this yet.
# Region Inference
Region inference is particularly tricky because it always succeeds "in
the moment" and simply registers a constraint. Then, at the end, we
can compute the full graph and report errors, so we need to be able to
store and later report what gave rise to the conflicting constraints.
# Subtype Trace
Determing whether `T1 <: T2` often involves a number of subtypes and
subconstraints along the way. A "TypeTrace" is an extended version
of an origin that traces the types and other values that were being
compared. It is not necessarily comprehensive (in fact, at the time of
this writing it only tracks the root values being compared) but I'd
like to extend it to include significant "waypoints". For example, if
you are comparing `(T1, T2) <: (T3, T4)`, and the problem is that `T2
<: T4` fails, I'd like the trace to include enough information to say
"in the 2nd element of the tuple". Similarly, failures when comparing
arguments or return types in fn types should be able to cite the
specific position, etc.
# Reality vs plan
Of course, there is still a LOT of code in typeck that has yet to be
ported to this system, and which relies on string concatenation at the
time of error detection.
*/
use std::prelude::*;
use middle::ty;
use middle::ty::Region;
use middle::typeck::infer;
use middle::typeck::infer::InferCtxt;
use middle::typeck::infer::TypeTrace;
use middle::typeck::infer::TypeOrigin;
use middle::typeck::infer::SubregionOrigin;
use middle::typeck::infer::RegionVariableOrigin;
use middle::typeck::infer::Types;
use middle::typeck::infer::TraitRefs;
use middle::typeck::infer::ValuePairs;
use middle::typeck::infer::region_inference::RegionResolutionError;
use middle::typeck::infer::region_inference::ConcreteFailure;
use middle::typeck::infer::region_inference::SubSupConflict;
use middle::typeck::infer::region_inference::SupSupConflict;
use syntax::opt_vec;
use syntax::opt_vec::OptVec;
use util::ppaux::UserString;
use util::ppaux::note_and_explain_region;
pub trait ErrorReporting {
pub fn report_region_errors(@mut self,
errors: &OptVec<RegionResolutionError>);
pub fn report_and_explain_type_error(@mut self,
trace: TypeTrace,
terr: &ty::type_err);
fn values_str(@mut self, values: &ValuePairs) -> Option<~str>;
fn expected_found_str<T:UserString+Resolvable>(
@mut self,
exp_found: &ty::expected_found<T>)
-> Option<~str>;
fn report_concrete_failure(@mut self,
origin: SubregionOrigin,
sub: Region,
sup: Region);
fn report_sub_sup_conflict(@mut self,
var_origin: RegionVariableOrigin,
sub_origin: SubregionOrigin,
sub_region: Region,
sup_origin: SubregionOrigin,
sup_region: Region);
fn report_sup_sup_conflict(@mut self,
var_origin: RegionVariableOrigin,
origin1: SubregionOrigin,
region1: Region,
origin2: SubregionOrigin,
region2: Region);
}
impl ErrorReporting for InferCtxt {
pub fn report_region_errors(@mut self,
errors: &OptVec<RegionResolutionError>) {
for errors.iter().advance |error| {
match *error {
ConcreteFailure(origin, sub, sup) => {
self.report_concrete_failure(origin, sub, sup);
}
SubSupConflict(var_origin,
sub_origin, sub_r,
sup_origin, sup_r) => {
self.report_sub_sup_conflict(var_origin,
sub_origin, sub_r,
sup_origin, sup_r);
}
SupSupConflict(var_origin,
origin1, r1,
origin2, r2) => {
self.report_sup_sup_conflict(var_origin,
origin1, r1,
origin2, r2);
}
}
}
}
pub fn report_and_explain_type_error(@mut self,
trace: TypeTrace,
terr: &ty::type_err) {
let tcx = self.tcx;
let expected_found_str = match self.values_str(&trace.values) {
Some(v) => v,
None => {
return; /* derived error */
}
};
let message_root_str = match trace.origin {
infer::Misc(_) => "mismatched types",
infer::MethodCompatCheck(_) => "method not compatible with trait",
infer::ExprAssignable(_) => "mismatched types",
infer::RelateTraitRefs(_) => "mismatched traits",
infer::RelateSelfType(_) => "mismatched types",
infer::MatchExpression(_) => "match arms have incompatible types",
infer::IfExpression(_) => "if and else have incompatible types",
};
self.tcx.sess.span_err(
trace.origin.span(),
fmt!("%s: %s (%s)",
message_root_str,
expected_found_str,
ty::type_err_to_str(tcx, terr)));
ty::note_and_explain_type_err(self.tcx, terr);
}
fn values_str(@mut self, values: &ValuePairs) -> Option<~str> {
/*!
* Returns a string of the form "expected `%s` but found `%s`",
* or None if this is a derived error.
*/
match *values {
infer::Types(ref exp_found) => {
self.expected_found_str(exp_found)
}
infer::TraitRefs(ref exp_found) => {
self.expected_found_str(exp_found)
}
}
}
fn expected_found_str<T:UserString+Resolvable>(
@mut self,
exp_found: &ty::expected_found<T>)
-> Option<~str>
{
let expected = exp_found.expected.resolve(self);
if expected.contains_error() {
return None;
}
let found = exp_found.found.resolve(self);
if found.contains_error() {
return None;
}
Some(fmt!("expected `%s` but found `%s`",
expected.user_string(self.tcx),
found.user_string(self.tcx)))
}
fn report_concrete_failure(@mut self,
origin: SubregionOrigin,
sub: Region,
sup: Region) {
match origin {
infer::Subtype(trace) => {
let terr = ty::terr_regions_does_not_outlive(sup, sub);
self.report_and_explain_type_error(trace, &terr);
}
infer::Reborrow(span) => {
self.tcx.sess.span_err(
span,
"lifetime of borrowed pointer outlines \
lifetime of borrowed content...");
note_and_explain_region(
self.tcx,
"...the borrowed pointer is valid for ",
sub,
"...");
note_and_explain_region(
self.tcx,
"...but the borrowed content is only valid for ",
sup,
"");
}
infer::InvokeClosure(span) => {
self.tcx.sess.span_err(
span,
"cannot invoke closure outside of its lifetime");
note_and_explain_region(
self.tcx,
"the closure is only valid for ",
sup,
"");
}
infer::DerefPointer(span) => {
self.tcx.sess.span_err(
span,
"dereference of reference outside its lifetime");
note_and_explain_region(
self.tcx,
"the reference is only valid for ",
sup,
"");
}
infer::FreeVariable(span) => {
self.tcx.sess.span_err(
span,
"captured variable does not outlive the enclosing closure");
note_and_explain_region(
self.tcx,
"captured variable is valid for ",
sup,
"");
note_and_explain_region(
self.tcx,
"closure is valid for ",
sub,
"");
}
infer::IndexSlice(span) => {
self.tcx.sess.span_err(
span,
fmt!("index of slice outside its lifetime"));
note_and_explain_region(
self.tcx,
"the slice is only valid for ",
sup,
"");
}
infer::RelateObjectBound(span) => {
self.tcx.sess.span_err(
span,
"lifetime of the source pointer does not outlive \
lifetime bound of the object type");
note_and_explain_region(
self.tcx,
"object type is valid for ",
sub,
"");
note_and_explain_region(
self.tcx,
"source pointer is only valid for ",
sup,
"");
}
infer::CallRcvr(span) => {
self.tcx.sess.span_err(
span,
"lifetime of method receiver does not outlive \
the method call");
note_and_explain_region(
self.tcx,
"the receiver is only valid for ",
sup,
"");
}
infer::CallArg(span) => {
self.tcx.sess.span_err(
span,
"lifetime of function argument does not outlive \
the function call");
note_and_explain_region(
self.tcx,
"the function argument is only valid for ",
sup,
"");
}
infer::CallReturn(span) => {
self.tcx.sess.span_err(
span,
"lifetime of return value does not outlive \
the function call");
note_and_explain_region(
self.tcx,
"the return value is only valid for ",
sup,
"");
}
infer::AddrOf(span) => {
self.tcx.sess.span_err(
span,
"borrowed pointer is not valid \
at the time of borrow");
note_and_explain_region(
self.tcx,
"the borrow is only valid for ",
sup,
"");
}
infer::AutoBorrow(span) => {
self.tcx.sess.span_err(
span,
"automatically borrowed pointer is not valid \
at the time of borrow");
note_and_explain_region(
self.tcx,
"the automatic borrow is only valid for ",
sup,
"");
}
infer::BindingTypeIsNotValidAtDecl(span) => {
self.tcx.sess.span_err(
span,
"lifetime of variable does not enclose its declaration");
note_and_explain_region(
self.tcx,
"the variable is only valid for ",
sup,
"");
}
infer::ReferenceOutlivesReferent(ty, span) => {
self.tcx.sess.span_err(
origin.span(),
fmt!("in type `%s`, pointer has a longer lifetime than \
the data it references",
ty.user_string(self.tcx)));
note_and_explain_region(
self.tcx,
"the pointer is valid for ",
sub,
"");
note_and_explain_region(
self.tcx,
"but the referenced data is only valid for ",
sup,
"");
}
}
}
fn report_sub_sup_conflict(@mut self,
var_origin: RegionVariableOrigin,
sub_origin: SubregionOrigin,
sub_region: Region,
sup_origin: SubregionOrigin,
sup_region: Region) {
self.tcx.sess.span_err(
var_origin.span(),
fmt!("cannot infer an appropriate lifetime \
due to conflicting requirements"));
note_and_explain_region(
self.tcx,
"first, the lifetime cannot outlive ",
sup_region,
"...");
self.tcx.sess.span_note(
sup_origin.span(),
fmt!("...due to the following expression"));
note_and_explain_region(
self.tcx,
"but, the lifetime must be valid for ",
sub_region,
"...");
self.tcx.sess.span_note(
sub_origin.span(),
fmt!("...due to the following expression"));
}
fn report_sup_sup_conflict(@mut self,
var_origin: RegionVariableOrigin,
origin1: SubregionOrigin,
region1: Region,
origin2: SubregionOrigin,
region2: Region) {
self.tcx.sess.span_err(
var_origin.span(),
fmt!("cannot infer an appropriate lifetime \
due to conflicting requirements"));
note_and_explain_region(
self.tcx,
"first, the lifetime must be contained by ",
region1,
"...");
self.tcx.sess.span_note(
origin1.span(),
fmt!("...due to the following expression"));
note_and_explain_region(
self.tcx,
"but, the lifetime must also be contained by ",
region2,
"...");
self.tcx.sess.span_note(
origin2.span(),
fmt!("...due to the following expression"));
}
}
trait Resolvable {
fn resolve(&self, infcx: @mut InferCtxt) -> Self;
fn contains_error(&self) -> bool;
}
impl Resolvable for ty::t {
fn resolve(&self, infcx: @mut InferCtxt) -> ty::t {
infcx.resolve_type_vars_if_possible(*self)
}
fn contains_error(&self) -> bool {
ty::type_is_error(*self)
}
}
impl Resolvable for @ty::TraitRef {
fn resolve(&self, infcx: @mut InferCtxt) -> @ty::TraitRef {
@infcx.resolve_type_vars_in_trait_ref_if_possible(*self)
}
fn contains_error(&self) -> bool {
ty::trait_ref_contains_error(*self)
}
}

13
src/librustc/middle/typeck/infer/glb.rs
View File

@ -18,6 +18,7 @@ use middle::typeck::infer::lub::Lub;
use middle::typeck::infer::sub::Sub;
use middle::typeck::infer::to_str::InferStr;
use middle::typeck::infer::{cres, InferCtxt};
use middle::typeck::infer::{TypeTrace, Subtype};
use middle::typeck::infer::fold_regions_in_sig;
use middle::typeck::isr_alist;
use syntax::ast;
@ -37,7 +38,7 @@ impl Combine for Glb {
fn infcx(&self) -> @mut InferCtxt { self.infcx }
fn tag(&self) -> ~str { ~"glb" }
fn a_is_expected(&self) -> bool { self.a_is_expected }
fn span(&self) -> span { self.span }
fn trace(&self) -> TypeTrace { self.trace }
fn sub(&self) -> Sub { Sub(**self) }
fn lub(&self) -> Lub { Lub(**self) }
@ -127,9 +128,7 @@ impl Combine for Glb {
a.inf_str(self.infcx),
b.inf_str(self.infcx));
do indent {
self.infcx.region_vars.glb_regions(self.span, a, b)
}
Ok(self.infcx.region_vars.glb_regions(Subtype(self.trace), a, b))
}
fn contraregions(&self, a: ty::Region, b: ty::Region)
@ -181,11 +180,11 @@ impl Combine for Glb {
// Instantiate each bound region with a fresh region variable.
let (a_with_fresh, a_isr) =
self.infcx.replace_bound_regions_with_fresh_regions(
self.span, a);
self.trace, a);
let a_vars = var_ids(self, a_isr);
let (b_with_fresh, b_isr) =
self.infcx.replace_bound_regions_with_fresh_regions(
self.span, b);
self.trace, b);
let b_vars = var_ids(self, b_isr);
// Collect constraints.
@ -277,7 +276,7 @@ impl Combine for Glb {
}
this.infcx.tcx.sess.span_bug(
this.span,
this.trace.origin.span(),
fmt!("could not find original bound region for %?", r));
}

2
src/librustc/middle/typeck/infer/lattice.rs
View File

@ -530,7 +530,7 @@ pub fn var_ids<T:Combine>(this: &T, isr: isr_alist) -> ~[RegionVid] {
ty::re_infer(ty::ReVar(r)) => { result.push(r); }
r => {
this.infcx().tcx.sess.span_bug(
this.span(),
this.trace().origin.span(),
fmt!("Found non-region-vid: %?", r));
}
}

13
src/librustc/middle/typeck/infer/lub.rs
View File

@ -19,6 +19,7 @@ use middle::typeck::infer::sub::Sub;
use middle::typeck::infer::to_str::InferStr;
use middle::typeck::infer::{cres, InferCtxt};
use middle::typeck::infer::fold_regions_in_sig;
use middle::typeck::infer::{TypeTrace, Subtype};
use middle::typeck::isr_alist;
use util::common::indent;
use util::ppaux::mt_to_str;
@ -44,7 +45,7 @@ impl Combine for Lub {
fn infcx(&self) -> @mut InferCtxt { self.infcx }
fn tag(&self) -> ~str { ~"lub" }
fn a_is_expected(&self) -> bool { self.a_is_expected }
fn span(&self) -> span { self.span }
fn trace(&self) -> TypeTrace { self.trace }
fn sub(&self) -> Sub { Sub(**self) }
fn lub(&self) -> Lub { Lub(**self) }
@ -119,9 +120,7 @@ impl Combine for Lub {
a.inf_str(self.infcx),
b.inf_str(self.infcx));
do indent {
self.infcx.region_vars.lub_regions(self.span, a, b)
}
Ok(self.infcx.region_vars.lub_regions(Subtype(self.trace), a, b))
}
fn fn_sigs(&self, a: &ty::FnSig, b: &ty::FnSig) -> cres<ty::FnSig> {
@ -137,10 +136,10 @@ impl Combine for Lub {
// Instantiate each bound region with a fresh region variable.
let (a_with_fresh, a_isr) =
self.infcx.replace_bound_regions_with_fresh_regions(
self.span, a);
self.trace, a);
let (b_with_fresh, _) =
self.infcx.replace_bound_regions_with_fresh_regions(
self.span, b);
self.trace, b);
// Collect constraints.
let sig0 = if_ok!(super_fn_sigs(self, &a_with_fresh, &b_with_fresh));
@ -196,7 +195,7 @@ impl Combine for Lub {
}
this.infcx.tcx.sess.span_bug(
this.span,
this.trace.origin.span(),
fmt!("Region %? is not associated with \
any bound region from A!", r0));
}

648
src/librustc/middle/typeck/infer/mod.rs
View File

@ -8,239 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
/*!
# Type inference engine
This is loosely based on standard HM-type inference, but with an
extension to try and accommodate subtyping. There is nothing
principled about this extension; it's sound---I hope!---but it's a
heuristic, ultimately, and does not guarantee that it finds a valid
typing even if one exists (in fact, there are known scenarios where it
fails, some of which may eventually become problematic).
## Key idea
The main change is that each type variable T is associated with a
lower-bound L and an upper-bound U. L and U begin as bottom and top,
respectively, but gradually narrow in response to new constraints
being introduced. When a variable is finally resolved to a concrete
type, it can (theoretically) select any type that is a supertype of L
and a subtype of U.
There are several critical invariants which we maintain:
- the upper-bound of a variable only becomes lower and the lower-bound
only becomes higher over time;
- the lower-bound L is always a subtype of the upper bound U;
- the lower-bound L and upper-bound U never refer to other type variables,
but only to types (though those types may contain type variables).
> An aside: if the terms upper- and lower-bound confuse you, think of
> "supertype" and "subtype". The upper-bound is a "supertype"
> (super=upper in Latin, or something like that anyway) and the lower-bound
> is a "subtype" (sub=lower in Latin). I find it helps to visualize
> a simple class hierarchy, like Java minus interfaces and
> primitive types. The class Object is at the root (top) and other
> types lie in between. The bottom type is then the Null type.
> So the tree looks like:
>
> Object
> / \
> String Other
> \ /
> (null)
>
> So the upper bound type is the "supertype" and the lower bound is the
> "subtype" (also, super and sub mean upper and lower in Latin, or something
> like that anyway).
## Satisfying constraints
At a primitive level, there is only one form of constraint that the
inference understands: a subtype relation. So the outside world can
say "make type A a subtype of type B". If there are variables
involved, the inferencer will adjust their upper- and lower-bounds as
needed to ensure that this relation is satisfied. (We also allow "make
type A equal to type B", but this is translated into "A <: B" and "B
<: A")
As stated above, we always maintain the invariant that type bounds
never refer to other variables. This keeps the inference relatively
simple, avoiding the scenario of having a kind of graph where we have
to pump constraints along and reach a fixed point, but it does impose
some heuristics in the case where the user is relating two type
variables A <: B.
Combining two variables such that variable A will forever be a subtype
of variable B is the trickiest part of the algorithm because there is
often no right choice---that is, the right choice will depend on
future constraints which we do not yet know. The problem comes about
because both A and B have bounds that can be adjusted in the future.
Let's look at some of the cases that can come up.
Imagine, to start, the best case, where both A and B have an upper and
lower bound (that is, the bounds are not top nor bot respectively). In
that case, if we're lucky, A.ub <: B.lb, and so we know that whatever
A and B should become, they will forever have the desired subtyping
relation. We can just leave things as they are.
### Option 1: Unify
However, suppose that A.ub is *not* a subtype of B.lb. In
that case, we must make a decision. One option is to unify A
and B so that they are one variable whose bounds are:
UB = GLB(A.ub, B.ub)
LB = LUB(A.lb, B.lb)
(Note that we will have to verify that LB <: UB; if it does not, the
types are not intersecting and there is an error) In that case, A <: B
holds trivially because A==B. However, we have now lost some
flexibility, because perhaps the user intended for A and B to end up
as different types and not the same type.
Pictorally, what this does is to take two distinct variables with
(hopefully not completely) distinct type ranges and produce one with
the intersection.
B.ub B.ub
/\ /
A.ub / \ A.ub /
/ \ / \ \ /
/ X \ UB
/ / \ \ / \
/ / / \ / /
\ \ / / \ /
\ X / LB
\ / \ / / \
\ / \ / / \
A.lb B.lb A.lb B.lb
### Option 2: Relate UB/LB
Another option is to keep A and B as distinct variables but set their
bounds in such a way that, whatever happens, we know that A <: B will hold.
This can be achieved by ensuring that A.ub <: B.lb. In practice there
are two ways to do that, depicted pictorally here:
Before Option #1 Option #2
B.ub B.ub B.ub
/\ / \ / \
A.ub / \ A.ub /(B')\ A.ub /(B')\
/ \ / \ \ / / \ / /
/ X \ __UB____/ UB /
/ / \ \ / | | /
/ / / \ / | | /
\ \ / / /(A')| | /
\ X / / LB ______LB/
\ / \ / / / \ / (A')/ \
\ / \ / \ / \ \ / \
A.lb B.lb A.lb B.lb A.lb B.lb
In these diagrams, UB and LB are defined as before. As you can see,
the new ranges `A'` and `B'` are quite different from the range that
would be produced by unifying the variables.
### What we do now
Our current technique is to *try* (transactionally) to relate the
existing bounds of A and B, if there are any (i.e., if `UB(A) != top
&& LB(B) != bot`). If that succeeds, we're done. If it fails, then
we merge A and B into same variable.
This is not clearly the correct course. For example, if `UB(A) !=
top` but `LB(B) == bot`, we could conceivably set `LB(B)` to `UB(A)`
and leave the variables unmerged. This is sometimes the better
course, it depends on the program.
The main case which fails today that I would like to support is:
fn foo<T>(x: T, y: T) { ... }
fn bar() {
let x: @mut int = @mut 3;
let y: @int = @3;
foo(x, y);
}
In principle, the inferencer ought to find that the parameter `T` to
`foo(x, y)` is `@const int`. Today, however, it does not; this is
because the type variable `T` is merged with the type variable for
`X`, and thus inherits its UB/LB of `@mut int`. This leaves no
flexibility for `T` to later adjust to accommodate `@int`.
### What to do when not all bounds are present
In the prior discussion we assumed that A.ub was not top and B.lb was
not bot. Unfortunately this is rarely the case. Often type variables
have "lopsided" bounds. For example, if a variable in the program has
been initialized but has not been used, then its corresponding type
variable will have a lower bound but no upper bound. When that
variable is then used, we would like to know its upper bound---but we
don't have one! In this case we'll do different things depending on
how the variable is being used.
## Transactional support
Whenever we adjust merge variables or adjust their bounds, we always
keep a record of the old value. This allows the changes to be undone.
## Regions
I've only talked about type variables here, but region variables
follow the same principle. They have upper- and lower-bounds. A
region A is a subregion of a region B if A being valid implies that B
is valid. This basically corresponds to the block nesting structure:
the regions for outer block scopes are superregions of those for inner
block scopes.
## Integral and floating-point type variables
There is a third variety of type variable that we use only for
inferring the types of unsuffixed integer literals. Integral type
variables differ from general-purpose type variables in that there's
no subtyping relationship among the various integral types, so instead
of associating each variable with an upper and lower bound, we just
use simple unification. Each integer variable is associated with at
most one integer type. Floating point types are handled similarly to
integral types.
## GLB/LUB
Computing the greatest-lower-bound and least-upper-bound of two
types/regions is generally straightforward except when type variables
are involved. In that case, we follow a similar "try to use the bounds
when possible but otherwise merge the variables" strategy. In other
words, `GLB(A, B)` where `A` and `B` are variables will often result
in `A` and `B` being merged and the result being `A`.
## Type coercion
We have a notion of assignability which differs somewhat from
subtyping; in particular it may cause region borrowing to occur. See
the big comment later in this file on Type Coercion for specifics.
### In conclusion
I showed you three ways to relate `A` and `B`. There are also more,
of course, though I'm not sure if there are any more sensible options.
The main point is that there are various options, each of which
produce a distinct range of types for `A` and `B`. Depending on what
the correct values for A and B are, one of these options will be the
right choice: but of course we don't know the right values for A and B
yet, that's what we're trying to find! In our code, we opt to unify
(Option #1).
# Implementation details
We make use of a trait-like impementation strategy to consolidate
duplicated code between subtypes, GLB, and LUB computations. See the
section on "Type Combining" below for details.
*/
/*! See doc.rs for documentation */
pub use middle::ty::IntVarValue;
@ -260,11 +28,14 @@ use middle::typeck::infer::combine::{Combine, CombineFields, eq_tys};
use middle::typeck::infer::region_inference::{RegionVarBindings};
use middle::typeck::infer::resolve::{resolver};
use middle::typeck::infer::sub::Sub;
use middle::typeck::infer::lub::Lub;
use middle::typeck::infer::to_str::InferStr;
use middle::typeck::infer::unify::{ValsAndBindings, Root};
use middle::typeck::infer::error_reporting::ErrorReporting;
use middle::typeck::isr_alist;
use util::common::indent;
use util::ppaux::{bound_region_to_str, ty_to_str, trait_ref_to_str};
use util::ppaux::{bound_region_to_str, ty_to_str, trait_ref_to_str, Repr,
UserString};
use std::result;
use std::vec;
@ -275,17 +46,20 @@ use syntax::ast;
use syntax::codemap;
use syntax::codemap::span;
pub mod doc;
pub mod macros;
pub mod combine;
pub mod glb;
pub mod lattice;
pub mod lub;
#[path = "region_inference/mod.rs"]
pub mod region_inference;
pub mod resolve;
pub mod sub;
pub mod to_str;
pub mod unify;
pub mod coercion;
pub mod error_reporting;
pub type Bound<T> = Option<T>;
pub struct Bounds<T> {
@ -319,6 +93,133 @@ pub struct InferCtxt {
region_vars: RegionVarBindings,
}
/// Why did we require that the two types be related?
///
/// See `error_reporting.rs` for more details
pub enum TypeOrigin {
// Not yet categorized in a better way
Misc(span),
// Checking that method of impl is compatible with trait
MethodCompatCheck(span),
// Checking that this expression can be assigned where it needs to be
ExprAssignable(@ast::expr),
// Relating trait refs when resolving vtables
RelateTraitRefs(span),
// Relating trait refs when resolving vtables
RelateSelfType(span),
// Computing common supertype in a match expression
MatchExpression(span),
// Computing common supertype in an if expression
IfExpression(span),
}
/// See `error_reporting.rs` for more details
pub enum ValuePairs {
Types(ty::expected_found<ty::t>),
TraitRefs(ty::expected_found<@ty::TraitRef>),
}
/// The trace designates the path through inference that we took to
/// encounter an error or subtyping constraint.
///
/// See `error_reporting.rs` for more details.
pub struct TypeTrace {
origin: TypeOrigin,
values: ValuePairs,
}
/// The origin of a `r1 <= r2` constraint.
///
/// See `error_reporting.rs` for more details
pub enum SubregionOrigin {
// Arose from a subtyping relation
Subtype(TypeTrace),
// Invocation of closure must be within its lifetime
InvokeClosure(span),
// Dereference of borrowed pointer must be within its lifetime
DerefPointer(span),
// Closure bound must not outlive captured free variables
FreeVariable(span),
// Index into slice must be within its lifetime
IndexSlice(span),
// When casting `&'a T` to an `&'b Trait` object,
// relating `'a` to `'b`
RelateObjectBound(span),
// Creating a pointer `b` to contents of another borrowed pointer
Reborrow(span),
// (&'a &'b T) where a >= b
ReferenceOutlivesReferent(ty::t, span),
// A `ref b` whose region does not enclose the decl site
BindingTypeIsNotValidAtDecl(span),
// Regions appearing in a method receiver must outlive method call
CallRcvr(span),
// Regions appearing in a function argument must outlive func call
CallArg(span),
// Region in return type of invoked fn must enclose call
CallReturn(span),
// Region resulting from a `&` expr must enclose the `&` expr
AddrOf(span),
// An auto-borrow that does not enclose the expr where it occurs
AutoBorrow(span),
}
/// Reasons to create a region inference variable
///
/// See `error_reporting.rs` for more details
pub enum RegionVariableOrigin {
// Region variables created for ill-categorized reasons,
// mostly indicates places in need of refactoring
MiscVariable(span),
// Regions created by a `&P` or `[...]` pattern
PatternRegion(span),
// Regions created by `&` operator
AddrOfRegion(span),
// Regions created by `&[...]` literal
AddrOfSlice(span),
// Regions created as part of an autoref of a method receiver
Autoref(span),
// Regions created as part of an automatic coercion
Coercion(TypeTrace),
// Region variables created for bound regions
// in a function or method that is called
BoundRegionInFnCall(span, ty::bound_region),
// Region variables created for bound regions
// when doing subtyping/lub/glb computations
BoundRegionInFnType(span, ty::bound_region),
BoundRegionInTypeOrImpl(span),
BoundRegionInCoherence,
BoundRegionError(span),
}
pub enum fixup_err {
unresolved_int_ty(IntVid),
unresolved_ty(TyVid),
@ -364,16 +265,51 @@ pub fn new_infer_ctxt(tcx: ty::ctxt) -> @mut InferCtxt {
}
}
pub fn common_supertype(cx: @mut InferCtxt,
origin: TypeOrigin,
a_is_expected: bool,
a: ty::t,
b: ty::t)
-> ty::t {
/*!
* Computes the least upper-bound of `a` and `b`. If this is
* not possible, reports an error and returns ty::err.
*/
debug!("common_supertype(%s, %s)", a.inf_str(cx), b.inf_str(cx));
let trace = TypeTrace {
origin: origin,
values: Types(expected_found(a_is_expected, a, b))
};
let result = do cx.commit {
cx.lub(a_is_expected, trace).tys(a, b)
};
match result {
Ok(t) => t,
Err(ref err) => {
cx.report_and_explain_type_error(trace, err);
ty::mk_err()
}
}
}
pub fn mk_subty(cx: @mut InferCtxt,
a_is_expected: bool,
span: span,
origin: TypeOrigin,
a: ty::t,
b: ty::t)
-> ures {
debug!("mk_subty(%s <: %s)", a.inf_str(cx), b.inf_str(cx));
do indent {
do cx.commit {
cx.sub(a_is_expected, span).tys(a, b)
let trace = TypeTrace {
origin: origin,
values: Types(expected_found(a_is_expected, a, b))
};
cx.sub(a_is_expected, trace).tys(a, b)
}
}.to_ures()
}
@ -382,35 +318,40 @@ pub fn can_mk_subty(cx: @mut InferCtxt, a: ty::t, b: ty::t) -> ures {
debug!("can_mk_subty(%s <: %s)", a.inf_str(cx), b.inf_str(cx));
do indent {
do cx.probe {
cx.sub(true, codemap::dummy_sp()).tys(a, b)
let trace = TypeTrace {
origin: Misc(codemap::dummy_sp()),
values: Types(expected_found(true, a, b))
};
cx.sub(true, trace).tys(a, b)
}
}.to_ures()
}
pub fn mk_subr(cx: @mut InferCtxt,
a_is_expected: bool,
span: span,
origin: SubregionOrigin,
a: ty::Region,
b: ty::Region)
-> ures {
b: ty::Region) {
debug!("mk_subr(%s <: %s)", a.inf_str(cx), b.inf_str(cx));
do indent {
do cx.commit {
cx.sub(a_is_expected, span).regions(a, b)
}
}.to_ures()
cx.region_vars.start_snapshot();
cx.region_vars.make_subregion(origin, a, b);
cx.region_vars.commit();
}
pub fn mk_eqty(cx: @mut InferCtxt,
a_is_expected: bool,
span: span,
origin: TypeOrigin,
a: ty::t,
b: ty::t)
-> ures {
debug!("mk_eqty(%s <: %s)", a.inf_str(cx), b.inf_str(cx));
do indent {
do cx.commit {
let suber = cx.sub(a_is_expected, span);
let trace = TypeTrace {
origin: origin,
values: Types(expected_found(a_is_expected, a, b))
};
let suber = cx.sub(a_is_expected, trace);
eq_tys(&suber, a, b)
}
}.to_ures()
@ -418,31 +359,49 @@ pub fn mk_eqty(cx: @mut InferCtxt,
pub fn mk_sub_trait_refs(cx: @mut InferCtxt,
a_is_expected: bool,
span: span,
a: &ty::TraitRef,
b: &ty::TraitRef)
origin: TypeOrigin,
a: @ty::TraitRef,
b: @ty::TraitRef)
-> ures
{
debug!("mk_sub_trait_refs(%s <: %s)",
a.inf_str(cx), b.inf_str(cx));
do indent {
do cx.commit {
let suber = cx.sub(a_is_expected, span);
let trace = TypeTrace {
origin: origin,
values: TraitRefs(expected_found(a_is_expected, a, b))
};
let suber = cx.sub(a_is_expected, trace);
suber.trait_refs(a, b)
}
}.to_ures()
}
fn expected_found<T>(a_is_expected: bool,
a: T,
b: T) -> ty::expected_found<T> {
if a_is_expected {
ty::expected_found {expected: a, found: b}
} else {
ty::expected_found {expected: b, found: a}
}
}
pub fn mk_coercety(cx: @mut InferCtxt,
a_is_expected: bool,
span: span,
origin: TypeOrigin,
a: ty::t,
b: ty::t)
-> CoerceResult {
debug!("mk_coercety(%s -> %s)", a.inf_str(cx), b.inf_str(cx));
do indent {
do cx.commit {
Coerce(cx.combine_fields(a_is_expected, span)).tys(a, b)
let trace = TypeTrace {
origin: origin,
values: Types(expected_found(a_is_expected, a, b))
};
Coerce(cx.combine_fields(a_is_expected, trace)).tys(a, b)
}
}
}
@ -451,8 +410,11 @@ pub fn can_mk_coercety(cx: @mut InferCtxt, a: ty::t, b: ty::t) -> ures {
debug!("can_mk_coercety(%s -> %s)", a.inf_str(cx), b.inf_str(cx));
do indent {
do cx.probe {
let span = codemap::dummy_sp();
Coerce(cx.combine_fields(true, span)).tys(a, b)
let trace = TypeTrace {
origin: Misc(codemap::dummy_sp()),
values: Types(expected_found(true, a, b))
};
Coerce(cx.combine_fields(true, trace)).tys(a, b)
}
}.to_ures()
}
@ -535,15 +497,21 @@ struct Snapshot {
}
impl InferCtxt {
pub fn combine_fields(@mut self, a_is_expected: bool, span: span)
pub fn combine_fields(@mut self,
a_is_expected: bool,
trace: TypeTrace)
-> CombineFields {
CombineFields {infcx: self,
a_is_expected: a_is_expected,
span: span}
trace: trace}
}
pub fn sub(@mut self, a_is_expected: bool, span: span) -> Sub {
Sub(self.combine_fields(a_is_expected, span))
pub fn sub(@mut self, a_is_expected: bool, trace: TypeTrace) -> Sub {
Sub(self.combine_fields(a_is_expected, trace))
}
pub fn lub(@mut self, a_is_expected: bool, trace: TypeTrace) -> Lub {
Lub(self.combine_fields(a_is_expected, trace))
}
pub fn in_snapshot(&self) -> bool {
@ -663,31 +631,13 @@ impl InferCtxt {
ty::mk_float_var(self.tcx, self.next_float_var_id())
}
pub fn next_region_var_nb(&mut self, span: span) -> ty::Region {
ty::re_infer(ty::ReVar(self.region_vars.new_region_var(span)))
pub fn next_region_var(&mut self, origin: RegionVariableOrigin) -> ty::Region {
ty::re_infer(ty::ReVar(self.region_vars.new_region_var(origin)))
}
pub fn next_region_var_with_lb(&mut self,
span: span,
lb_region: ty::Region)
-> ty::Region {
let region_var = self.next_region_var_nb(span);
// add lb_region as a lower bound on the newly built variable
assert!(self.region_vars.make_subregion(span,
lb_region,
region_var).is_ok());
return region_var;
}
pub fn next_region_var(&mut self, span: span, scope_id: ast::node_id)
-> ty::Region {
self.next_region_var_with_lb(span, ty::re_scope(scope_id))
}
pub fn resolve_regions(&mut self) {
self.region_vars.resolve_regions();
pub fn resolve_regions(@mut self) {
let errors = self.region_vars.resolve_regions();
self.report_region_errors(&errors); // see error_reporting.rs
}
pub fn ty_to_str(@mut self, t: ty::t) -> ~str {
@ -809,17 +759,13 @@ impl InferCtxt {
}
pub fn replace_bound_regions_with_fresh_regions(&mut self,
span: span,
trace: TypeTrace,
fsig: &ty::FnSig)
-> (ty::FnSig,
isr_alist) {
-> (ty::FnSig, isr_alist) {
let(isr, _, fn_sig) =
replace_bound_regions_in_fn_sig(self.tcx, @Nil, None, fsig, |br| {
// N.B.: The name of the bound region doesn't have anything to
// do with the region variable that's created for it. The
// only thing we're doing with `br` here is using it in the
// debug message.
let rvar = self.next_region_var_nb(span);
let rvar = self.next_region_var(
BoundRegionInFnType(trace.origin.span(), br));
debug!("Bound region %s maps to %?",
bound_region_to_str(self.tcx, "", false, br),
rvar);
@ -838,3 +784,125 @@ pub fn fold_regions_in_sig(
ty::fold_regions(tcx, t, |r, in_fn| fldr(r, in_fn))
}
}
impl TypeTrace {
pub fn span(&self) -> span {
self.origin.span()
}
}
impl Repr for TypeTrace {
fn repr(&self, tcx: ty::ctxt) -> ~str {
fmt!("TypeTrace(%s)", self.origin.repr(tcx))
}
}
impl TypeOrigin {
pub fn span(&self) -> span {
match *self {
MethodCompatCheck(span) => span,
ExprAssignable(expr) => expr.span,
Misc(span) => span,
RelateTraitRefs(span) => span,
RelateSelfType(span) => span,
MatchExpression(span) => span,
IfExpression(span) => span,
}
}
}
impl Repr for TypeOrigin {
fn repr(&self, tcx: ty::ctxt) -> ~str {
match *self {
MethodCompatCheck(a) => fmt!("MethodCompatCheck(%s)", a.repr(tcx)),
ExprAssignable(a) => fmt!("ExprAssignable(%s)", a.repr(tcx)),
Misc(a) => fmt!("Misc(%s)", a.repr(tcx)),
RelateTraitRefs(a) => fmt!("RelateTraitRefs(%s)", a.repr(tcx)),
RelateSelfType(a) => fmt!("RelateSelfType(%s)", a.repr(tcx)),
MatchExpression(a) => fmt!("MatchExpression(%s)", a.repr(tcx)),
IfExpression(a) => fmt!("IfExpression(%s)", a.repr(tcx)),
}
}
}
impl SubregionOrigin {
pub fn span(&self) -> span {
match *self {
Subtype(a) => a.span(),
InvokeClosure(a) => a,
DerefPointer(a) => a,
FreeVariable(a) => a,
IndexSlice(a) => a,
RelateObjectBound(a) => a,
Reborrow(a) => a,
ReferenceOutlivesReferent(_, a) => a,
BindingTypeIsNotValidAtDecl(a) => a,
CallRcvr(a) => a,
CallArg(a) => a,
CallReturn(a) => a,
AddrOf(a) => a,
AutoBorrow(a) => a,
}
}
}
impl Repr for SubregionOrigin {
fn repr(&self, tcx: ty::ctxt) -> ~str {
match *self {
Subtype(a) => fmt!("Subtype(%s)", a.repr(tcx)),
InvokeClosure(a) => fmt!("InvokeClosure(%s)", a.repr(tcx)),
DerefPointer(a) => fmt!("DerefPointer(%s)", a.repr(tcx)),
FreeVariable(a) => fmt!("FreeVariable(%s)", a.repr(tcx)),
IndexSlice(a) => fmt!("IndexSlice(%s)", a.repr(tcx)),
RelateObjectBound(a) => fmt!("RelateObjectBound(%s)", a.repr(tcx)),
Reborrow(a) => fmt!("Reborrow(%s)", a.repr(tcx)),
ReferenceOutlivesReferent(_, a) => fmt!("ReferenceOutlivesReferent(%s)", a.repr(tcx)),
BindingTypeIsNotValidAtDecl(a) => fmt!("BindingTypeIsNotValidAtDecl(%s)", a.repr(tcx)),
CallRcvr(a) => fmt!("CallRcvr(%s)", a.repr(tcx)),
CallArg(a) => fmt!("CallArg(%s)", a.repr(tcx)),
CallReturn(a) => fmt!("CallReturn(%s)", a.repr(tcx)),
AddrOf(a) => fmt!("AddrOf(%s)", a.repr(tcx)),
AutoBorrow(a) => fmt!("AutoBorrow(%s)", a.repr(tcx)),
}
}
}
impl RegionVariableOrigin {
pub fn span(&self) -> span {
match *self {
MiscVariable(a) => a,
PatternRegion(a) => a,
AddrOfRegion(a) => a,
AddrOfSlice(a) => a,
Autoref(a) => a,
Coercion(a) => a.span(),
BoundRegionInFnCall(a, _) => a,
BoundRegionInFnType(a, _) => a,
BoundRegionInTypeOrImpl(a) => a,
BoundRegionInCoherence => codemap::dummy_sp(),
BoundRegionError(a) => a,
}
}
}
impl Repr for RegionVariableOrigin {
fn repr(&self, tcx: ty::ctxt) -> ~str {
match *self {
MiscVariable(a) => fmt!("MiscVariable(%s)", a.repr(tcx)),
PatternRegion(a) => fmt!("PatternRegion(%s)", a.repr(tcx)),
AddrOfRegion(a) => fmt!("AddrOfRegion(%s)", a.repr(tcx)),
AddrOfSlice(a) => fmt!("AddrOfSlice(%s)", a.repr(tcx)),
Autoref(a) => fmt!("Autoref(%s)", a.repr(tcx)),
Coercion(a) => fmt!("Coercion(%s)", a.repr(tcx)),
BoundRegionInFnCall(a, b) => fmt!("BoundRegionInFnCall(%s,%s)",
a.repr(tcx), b.repr(tcx)),
BoundRegionInFnType(a, b) => fmt!("BoundRegionInFnType(%s,%s)",
a.repr(tcx), b.repr(tcx)),
BoundRegionInTypeOrImpl(a) => fmt!("BoundRegionInTypeOrImpl(%s)",
a.repr(tcx)),
BoundRegionInCoherence => fmt!("BoundRegionInCoherence"),
BoundRegionError(a) => fmt!("BoundRegionError(%s)", a.repr(tcx)),
}
}
}

773
src/librustc/middle/typeck/infer/region_inference/doc.rs Normal file
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@ -0,0 +1,773 @@
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
/*!
Region inference module.
# Terminology
Note that we use the terms region and lifetime interchangeably,
though the term `lifetime` is preferred.
# Introduction
Region inference uses a somewhat more involved algorithm than type
inference. It is not the most efficient thing ever written though it
seems to work well enough in practice (famous last words). The reason
that we use a different algorithm is because, unlike with types, it is
impractical to hand-annotate with regions (in some cases, there aren't
even the requisite syntactic forms). So we have to get it right, and
it's worth spending more time on a more involved analysis. Moreover,
regions are a simpler case than types: they don't have aggregate
structure, for example.
Unlike normal type inference, which is similar in spirit to H-M and thus
works progressively, the region type inference works by accumulating
constraints over the course of a function. Finally, at the end of
processing a function, we process and solve the constraints all at
once.
The constraints are always of one of three possible forms:
- ConstrainVarSubVar(R_i, R_j) states that region variable R_i
must be a subregion of R_j
- ConstrainRegSubVar(R, R_i) states that the concrete region R
(which must not be a variable) must be a subregion of the varibale R_i
- ConstrainVarSubReg(R_i, R) is the inverse
# Building up the constraints
Variables and constraints are created using the following methods:
- `new_region_var()` creates a new, unconstrained region variable;
- `make_subregion(R_i, R_j)` states that R_i is a subregion of R_j
- `lub_regions(R_i, R_j) -> R_k` returns a region R_k which is
the smallest region that is greater than both R_i and R_j
- `glb_regions(R_i, R_j) -> R_k` returns a region R_k which is
the greatest region that is smaller than both R_i and R_j
The actual region resolution algorithm is not entirely
obvious, though it is also not overly complex.
## Snapshotting
It is also permitted to try (and rollback) changes to the graph. This
is done by invoking `start_snapshot()`, which returns a value. Then
later you can call `rollback_to()` which undoes the work.
Alternatively, you can call `commit()` which ends all snapshots.
Snapshots can be recursive---so you can start a snapshot when another
is in progress, but only the root snapshot can "commit".
# Resolving constraints
The constraint resolution algorithm is not super complex but also not
entirely obvious. Here I describe the problem somewhat abstractly,
then describe how the current code works. There may be other, smarter
ways of doing this with which I am unfamiliar and can't be bothered to
research at the moment. - NDM
## The problem
Basically our input is a directed graph where nodes can be divided
into two categories: region variables and concrete regions. Each edge
`R -> S` in the graph represents a constraint that the region `R` is a
subregion of the region `S`.
Region variable nodes can have arbitrary degree. There is one region
variable node per region variable.
Each concrete region node is associated with some, well, concrete
region: e.g., a free lifetime, or the region for a particular scope.
Note that there may be more than one concrete region node for a
particular region value. Moreover, because of how the graph is built,
we know that all concrete region nodes have either in-degree 1 or
out-degree 1.
Before resolution begins, we build up the constraints in a hashmap
that maps `Constraint` keys to spans. During resolution, we construct
the actual `Graph` structure that we describe here.
## Our current algorithm
We divide region variables into two groups: Expanding and Contracting.
Expanding region variables are those that have a concrete region
predecessor (direct or indirect). Contracting region variables are
all others.
We first resolve the values of Expanding region variables and then
process Contracting ones. We currently use an iterative, fixed-point
procedure (but read on, I believe this could be replaced with a linear
walk). Basically we iterate over the edges in the graph, ensuring
that, if the source of the edge has a value, then this value is a
subregion of the target value. If the target does not yet have a
value, it takes the value from the source. If the target already had
a value, then the resulting value is Least Upper Bound of the old and
new values. When we are done, each Expanding node will have the
smallest region that it could possibly have and still satisfy the
constraints.
We next process the Contracting nodes. Here we again iterate over the
edges, only this time we move values from target to source (if the
source is a Contracting node). For each contracting node, we compute
its value as the GLB of all its successors. Basically contracting
nodes ensure that there is overlap between their successors; we will
ultimately infer the largest overlap possible.
# The Region Hierarchy
## Without closures
Let's first consider the region hierarchy without thinking about
closures, because they add a lot of complications. The region
hierarchy *basically* mirrors the lexical structure of the code.
There is a region for every piece of 'evaluation' that occurs, meaning
every expression, block, and pattern (patterns are considered to
"execute" by testing the value they are applied to and creating any
relevant bindings). So, for example:
fn foo(x: int, y: int) { // -+
// +------------+ // |
// | +-----+ // |
// | +-+ +-+ +-+ // |
// | | | | | | | // |
// v v v v v v v // |
let z = x + y; // |
... // |
} // -+
fn bar() { ... }
In this example, there is a region for the fn body block as a whole,
and then a subregion for the declaration of the local variable.
Within that, there are sublifetimes for the assignment pattern and
also the expression `x + y`. The expression itself has sublifetimes
for evaluating `x` and and `y`.
## Function calls
Function calls are a bit tricky. I will describe how we handle them
*now* and then a bit about how we can improve them (Issue #6268).
Consider a function call like `func(expr1, expr2)`, where `func`,
`arg1`, and `arg2` are all arbitrary expressions. Currently,
we construct a region hierarchy like:
+----------------+
| |
+--+ +---+ +---+|
v v v v v vv
func(expr1, expr2)
Here you can see that the call as a whole has a region and the
function plus arguments are subregions of that. As a side-effect of
this, we get a lot of spurious errors around nested calls, in
particular when combined with `&mut` functions. For example, a call
like this one
self.foo(self.bar())
where both `foo` and `bar` are `&mut self` functions will always yield
an error.
Here is a more involved example (which is safe) so we can see what's
going on:
struct Foo { f: uint, g: uint }
...
fn add(p: &mut uint, v: uint) {
*p += v;
}
...
fn inc(p: &mut uint) -> uint {
*p += 1; *p
}
fn weird() {
let mut x: ~Foo = ~Foo { ... };
'a: add(&mut (*x).f,
'b: inc(&mut (*x).f)) // (*)
}
The important part is the line marked `(*)` which contains a call to
`add()`. The first argument is a mutable borrow of the field `f`. The
second argument also borrows the field `f`. Now, in the current borrow
checker, the first borrow is given the lifetime of the call to
`add()`, `'a`. The second borrow is given the lifetime of `'b` of the
call to `inc()`. Because `'b` is considered to be a sublifetime of
`'a`, an error is reported since there are two co-existing mutable
borrows of the same data.
However, if we were to examine the lifetimes a bit more carefully, we
can see that this error is unnecessary. Let's examine the lifetimes
involved with `'a` in detail. We'll break apart all the steps involved
in a call expression:
'a: {
'a_arg1: let a_temp1: ... = add;
'a_arg2: let a_temp2: &'a mut uint = &'a mut (*x).f;
'a_arg3: let a_temp3: uint = {
let b_temp1: ... = inc;
let b_temp2: &'b = &'b mut (*x).f;
'b_call: b_temp1(b_temp2)
};
'a_call: a_temp1(a_temp2, a_temp3) // (**)
}
Here we see that the lifetime `'a` includes a number of substatements.
In particular, there is this lifetime I've called `'a_call` that
corresponds to the *actual execution of the function `add()`*, after
all arguments have been evaluated. There is a corresponding lifetime
`'b_call` for the execution of `inc()`. If we wanted to be precise
about it, the lifetime of the two borrows should be `'a_call` and
`'b_call` respectively, since the borrowed pointers that were created
will not be dereferenced except during the execution itself.
However, this model by itself is not sound. The reason is that
while the two borrowed pointers that are created will never be used
simultaneously, it is still true that the first borrowed pointer is
*created* before the second argument is evaluated, and so even though
it will not be *dereferenced* during the evaluation of the second
argument, it can still be *invalidated* by that evaluation. Consider
this similar but unsound example:
struct Foo { f: uint, g: uint }
...
fn add(p: &mut uint, v: uint) {
*p += v;
}
...
fn consume(x: ~Foo) -> uint {
x.f + x.g
}
fn weird() {
let mut x: ~Foo = ~Foo { ... };
'a: add(&mut (*x).f, consume(x)) // (*)
}
In this case, the second argument to `add` actually consumes `x`, thus
invalidating the first argument.
So, for now, we exclude the `call` lifetimes from our model.
Eventually I would like to include them, but we will have to make the
borrow checker handle this situation correctly. In particular, if
there is a borrowed pointer created whose lifetime does not enclose
the borrow expression, we must issue sufficient restrictions to ensure
that the pointee remains valid.
## Adding closures
The other significant complication to the region hierarchy is
closures. I will describe here how closures should work, though some
of the work to implement this model is ongoing at the time of this
writing.
The body of closures are type-checked along with the function that
creates them. However, unlike other expressions that appear within the
function body, it is not entirely obvious when a closure body executes
with respect to the other expressions. This is because the closure
body will execute whenever the closure is called; however, we can
never know precisely when the closure will be called, especially
without some sort of alias analysis.
However, we can place some sort of limits on when the closure
executes. In particular, the type of every closure `fn:'r K` includes
a region bound `'r`. This bound indicates the maximum lifetime of that
closure; once we exit that region, the closure cannot be called
anymore. Therefore, we say that the lifetime of the closure body is a
sublifetime of the closure bound, but the closure body itself is unordered
with respect to other parts of the code.
For example, consider the following fragment of code:
'a: {
let closure: fn:'a() = || 'b: {
'c: ...
};
'd: ...
}
Here we have four lifetimes, `'a`, `'b`, `'c`, and `'d`. The closure
`closure` is bounded by the lifetime `'a`. The lifetime `'b` is the
lifetime of the closure body, and `'c` is some statement within the
closure body. Finally, `'d` is a statement within the outer block that
created the closure.
We can say that the closure body `'b` is a sublifetime of `'a` due to
the closure bound. By the usual lexical scoping conventions, the
statement `'c` is clearly a sublifetime of `'b`, and `'d` is a
sublifetime of `'d`. However, there is no ordering between `'c` and
`'d` per se (this kind of ordering between statements is actually only
an issue for dataflow; passes like the borrow checker must assume that
closures could execute at any time from the moment they are created
until they go out of scope).
### Complications due to closure bound inference
There is only one problem with the above model: in general, we do not
actually *know* the closure bounds during region inference! In fact,
closure bounds are almost always region variables! This is very tricky
because the inference system implicitly assumes that we can do things
like compute the LUB of two scoped lifetimes without needing to know
the values of any variables.
Here is an example to illustrate the problem:
fn identify<T>(x: T) -> T { x }
fn foo() { // 'foo is the function body
'a: {
let closure = identity(|| 'b: {
'c: ...
});
'd: closure();
}
'e: ...;
}
In this example, the closure bound is not explicit. At compile time,
we will create a region variable (let's call it `V0`) to represent the
closure bound.
The primary difficulty arises during the constraint propagation phase.
Imagine there is some variable with incoming edges from `'c` and `'d`.
This means that the value of the variable must be `LUB('c,
'd)`. However, without knowing what the closure bound `V0` is, we
can't compute the LUB of `'c` and `'d`! Any we don't know the closure
bound until inference is done.
The solution is to rely on the fixed point nature of inference.
Basically, when we must compute `LUB('c, 'd)`, we just use the current
value for `V0` as the closure's bound. If `V0`'s binding should
change, then we will do another round of inference, and the result of
`LUB('c, 'd)` will change.
One minor implication of this is that the graph does not in fact track
the full set of dependencies between edges. We cannot easily know
whether the result of a LUB computation will change, since there may
be indirect dependencies on other variables that are not reflected on
the graph. Therefore, we must *always* iterate over all edges when
doing the fixed point calculation, not just those adjacent to nodes
whose values have changed.
Were it not for this requirement, we could in fact avoid fixed-point
iteration altogether. In that universe, we could instead first
identify and remove strongly connected components (SCC) in the graph.
Note that such components must consist solely of region variables; all
of these variables can effectively be unified into a single variable.
Once SCCs are removed, we are left with a DAG. At this point, we
could walk the DAG in toplogical order once to compute the expanding
nodes, and again in reverse topological order to compute the
contracting nodes. However, as I said, this does not work given the
current treatment of closure bounds, but perhaps in the future we can
address this problem somehow and make region inference somewhat more
efficient. Note that this is solely a matter of performance, not
expressiveness.
# Skolemization and functions
One of the trickiest and most subtle aspects of regions is dealing
with the fact that region variables are bound in function types. I
strongly suggest that if you want to understand the situation, you
read this paper (which is, admittedly, very long, but you don't have
to read the whole thing):
http://research.microsoft.com/en-us/um/people/simonpj/papers/higher-rank/
Although my explanation will never compete with SPJ's (for one thing,
his is approximately 100 pages), I will attempt to explain the basic
problem and also how we solve it. Note that the paper only discusses
subtyping, not the computation of LUB/GLB.
The problem we are addressing is that there is a kind of subtyping
between functions with bound region parameters. Consider, for
example, whether the following relation holds:
fn(&'a int) <: &fn(&'b int)? (Yes, a => b)
The answer is that of course it does. These two types are basically
the same, except that in one we used the name `a` and one we used
the name `b`.
In the examples that follow, it becomes very important to know whether
a lifetime is bound in a function type (that is, is a lifetime
parameter) or appears free (is defined in some outer scope).
Therefore, from now on I will write the bindings explicitly, using a
notation like `fn<a>(&'a int)` to indicate that `a` is a lifetime
parameter.
Now let's consider two more function types. Here, we assume that the
`self` lifetime is defined somewhere outside and hence is not a
lifetime parameter bound by the function type (it "appears free"):
fn<a>(&'a int) <: &fn(&'self int)? (Yes, a => self)
This subtyping relation does in fact hold. To see why, you have to
consider what subtyping means. One way to look at `T1 <: T2` is to
say that it means that it is always ok to treat an instance of `T1` as
if it had the type `T2`. So, with our functions, it is always ok to
treat a function that can take pointers with any lifetime as if it
were a function that can only take a pointer with the specific
lifetime `&self`. After all, `&self` is a lifetime, after all, and
the function can take values of any lifetime.
You can also look at subtyping as the *is a* relationship. This amounts
to the same thing: a function that accepts pointers with any lifetime
*is a* function that accepts pointers with some specific lifetime.
So, what if we reverse the order of the two function types, like this:
fn(&'self int) <: &fn<a>(&'a int)? (No)
Does the subtyping relationship still hold? The answer of course is
no. In this case, the function accepts *only the lifetime `&self`*,
so it is not reasonable to treat it as if it were a function that
accepted any lifetime.
What about these two examples:
fn<a,b>(&'a int, &'b int) <: &fn<a>(&'a int, &'a int)? (Yes)
fn<a>(&'a int, &'a int) <: &fn<a,b>(&'a int, &'b int)? (No)
Here, it is true that functions which take two pointers with any two
lifetimes can be treated as if they only accepted two pointers with
the same lifetime, but not the reverse.
## The algorithm
Here is the algorithm we use to perform the subtyping check:
1. Replace all bound regions in the subtype with new variables
2. Replace all bound regions in the supertype with skolemized
equivalents. A "skolemized" region is just a new fresh region
name.
3. Check that the parameter and return types match as normal
4. Ensure that no skolemized regions 'leak' into region variables
visible from "the outside"
Let's walk through some examples and see how this algorithm plays out.
#### First example
We'll start with the first example, which was:
1. fn<a>(&'a T) <: &fn<b>(&'b T)? Yes: a -> b
After steps 1 and 2 of the algorithm we will have replaced the types
like so:
1. fn(&'A T) <: &fn(&'x T)?
Here the upper case `&A` indicates a *region variable*, that is, a
region whose value is being inferred by the system. I also replaced
`&b` with `&x`---I'll use letters late in the alphabet (`x`, `y`, `z`)
to indicate skolemized region names. We can assume they don't appear
elsewhere. Note that neither the sub- nor the supertype bind any
region names anymore (as indicated by the absence of `<` and `>`).
The next step is to check that the parameter types match. Because
parameters are contravariant, this means that we check whether:
&'x T <: &'A T
Region pointers are contravariant so this implies that
&A <= &x
must hold, where `<=` is the subregion relationship. Processing
*this* constrain simply adds a constraint into our graph that `&A <=
&x` and is considered successful (it can, for example, be satisfied by
choosing the value `&x` for `&A`).
So far we have encountered no error, so the subtype check succeeds.
#### The third example
Now let's look first at the third example, which was:
3. fn(&'self T) <: &fn<b>(&'b T)? No!
After steps 1 and 2 of the algorithm we will have replaced the types
like so:
3. fn(&'self T) <: &fn(&'x T)?
This looks pretty much the same as before, except that on the LHS
`&self` was not bound, and hence was left as-is and not replaced with
a variable. The next step is again to check that the parameter types
match. This will ultimately require (as before) that `&self` <= `&x`
must hold: but this does not hold. `self` and `x` are both distinct
free regions. So the subtype check fails.
#### Checking for skolemization leaks
You may be wondering about that mysterious last step in the algorithm.
So far it has not been relevant. The purpose of that last step is to
catch something like *this*:
fn<a>() -> fn(&'a T) <: &fn() -> fn<b>(&'b T)? No.
Here the function types are the same but for where the binding occurs.
The subtype returns a function that expects a value in precisely one
region. The supertype returns a function that expects a value in any
region. If we allow an instance of the subtype to be used where the
supertype is expected, then, someone could call the fn and think that
the return value has type `fn<b>(&'b T)` when it really has type
`fn(&'a T)` (this is case #3, above). Bad.
So let's step through what happens when we perform this subtype check.
We first replace the bound regions in the subtype (the supertype has
no bound regions). This gives us:
fn() -> fn(&'A T) <: &fn() -> fn<b>(&'b T)?
Now we compare the return types, which are covariant, and hence we have:
fn(&'A T) <: &fn<b>(&'b T)?
Here we skolemize the bound region in the supertype to yield:
fn(&'A T) <: &fn(&'x T)?
And then proceed to compare the argument types:
&'x T <: &'A T
&A <= &x
Finally, this is where it gets interesting! This is where an error
*should* be reported. But in fact this will not happen. The reason why
is that `A` is a variable: we will infer that its value is the fresh
region `x` and think that everything is happy. In fact, this behavior
is *necessary*, it was key to the first example we walked through.
The difference between this example and the first one is that the variable
`A` already existed at the point where the skolemization occurred. In
the first example, you had two functions:
fn<a>(&'a T) <: &fn<b>(&'b T)
and hence `&A` and `&x` were created "together". In general, the
intention of the skolemized names is that they are supposed to be
fresh names that could never be equal to anything from the outside.
But when inference comes into play, we might not be respecting this
rule.
So the way we solve this is to add a fourth step that examines the
constraints that refer to skolemized names. Basically, consider a
non-directed verison of the constraint graph. Let `Tainted(x)` be the
set of all things reachable from a skolemized variable `x`.
`Tainted(x)` should not contain any regions that existed before the
step at which the skolemization was performed. So this case here
would fail because `&x` was created alone, but is relatable to `&A`.
## Computing the LUB and GLB
The paper I pointed you at is written for Haskell. It does not
therefore considering subtyping and in particular does not consider
LUB or GLB computation. We have to consider this. Here is the
algorithm I implemented.
First though, let's discuss what we are trying to compute in more
detail. The LUB is basically the "common supertype" and the GLB is
"common subtype"; one catch is that the LUB should be the
*most-specific* common supertype and the GLB should be *most general*
common subtype (as opposed to any common supertype or any common
subtype).
Anyway, to help clarify, here is a table containing some
function pairs and their LUB/GLB:
```
Type 1 Type 2 LUB GLB
fn<a>(&a) fn(&X) fn(&X) fn<a>(&a)
fn(&A) fn(&X) -- fn<a>(&a)
fn<a,b>(&a, &b) fn<x>(&x, &x) fn<a>(&a, &a) fn<a,b>(&a, &b)
fn<a,b>(&a, &b, &a) fn<x,y>(&x, &y, &y) fn<a>(&a, &a, &a) fn<a,b,c>(&a,&b,&c)
```
### Conventions
I use lower-case letters (e.g., `&a`) for bound regions and upper-case
letters for free regions (`&A`). Region variables written with a
dollar-sign (e.g., `$a`). I will try to remember to enumerate the
bound-regions on the fn type as well (e.g., `fn<a>(&a)`).
### High-level summary
Both the LUB and the GLB algorithms work in a similar fashion. They
begin by replacing all bound regions (on both sides) with fresh region
inference variables. Therefore, both functions are converted to types
that contain only free regions. We can then compute the LUB/GLB in a
straightforward way, as described in `combine.rs`. This results in an
interim type T. The algorithms then examine the regions that appear
in T and try to, in some cases, replace them with bound regions to
yield the final result.
To decide whether to replace a region `R` that appears in `T` with a
bound region, the algorithms make use of two bits of information.
First is a set `V` that contains all region variables created as part
of the LUB/GLB computation. `V` will contain the region variables
created to replace the bound regions in the input types, but it also
contains 'intermediate' variables created to represent the LUB/GLB of
individual regions. Basically, when asked to compute the LUB/GLB of a
region variable with another region, the inferencer cannot oblige
immediately since the valuese of that variables are not known.
Therefore, it creates a new variable that is related to the two
regions. For example, the LUB of two variables `$x` and `$y` is a
fresh variable `$z` that is constrained such that `$x <= $z` and `$y
<= $z`. So `V` will contain these intermediate variables as well.
The other important factor in deciding how to replace a region in T is
the function `Tainted($r)` which, for a region variable, identifies
all regions that the region variable is related to in some way
(`Tainted()` made an appearance in the subtype computation as well).
### LUB
The LUB algorithm proceeds in three steps:
1. Replace all bound regions (on both sides) with fresh region
inference variables.
2. Compute the LUB "as normal", meaning compute the GLB of each
pair of argument types and the LUB of the return types and
so forth. Combine those to a new function type `F`.
3. Replace each region `R` that appears in `F` as follows:
- Let `V` be the set of variables created during the LUB
computational steps 1 and 2, as described in the previous section.
- If `R` is not in `V`, replace `R` with itself.
- If `Tainted(R)` contains a region that is not in `V`,
replace `R` with itself.
- Otherwise, select the earliest variable in `Tainted(R)` that originates
from the left-hand side and replace `R` with the bound region that
this variable was a replacement for.
So, let's work through the simplest example: `fn(&A)` and `fn<a>(&a)`.
In this case, `&a` will be replaced with `$a` and the interim LUB type
`fn($b)` will be computed, where `$b=GLB(&A,$a)`. Therefore, `V =
{$a, $b}` and `Tainted($b) = { $b, $a, &A }`. When we go to replace
`$b`, we find that since `&A \in Tainted($b)` is not a member of `V`,
we leave `$b` as is. When region inference happens, `$b` will be
resolved to `&A`, as we wanted.
Let's look at a more complex one: `fn(&a, &b)` and `fn(&x, &x)`. In
this case, we'll end up with a (pre-replacement) LUB type of `fn(&g,
&h)` and a graph that looks like:
```
$a $b *--$x
\ \ / /
\ $h-* /
$g-----------*
```
Here `$g` and `$h` are fresh variables that are created to represent
the LUB/GLB of things requiring inference. This means that `V` and
`Tainted` will look like:
```
V = {$a, $b, $g, $h, $x}
Tainted($g) = Tainted($h) = { $a, $b, $h, $g, $x }
```
Therefore we replace both `$g` and `$h` with `$a`, and end up
with the type `fn(&a, &a)`.
### GLB
The procedure for computing the GLB is similar. The difference lies
in computing the replacements for the various variables. For each
region `R` that appears in the type `F`, we again compute `Tainted(R)`
and examine the results:
1. If `R` is not in `V`, it is not replaced.
2. Else, if `Tainted(R)` contains only variables in `V`, and it
contains exactly one variable from the LHS and one variable from
the RHS, then `R` can be mapped to the bound version of the
variable from the LHS.
3. Else, if `Tainted(R)` contains no variable from the LHS and no
variable from the RHS, then `R` can be mapped to itself.
4. Else, `R` is mapped to a fresh bound variable.
These rules are pretty complex. Let's look at some examples to see
how they play out.
Out first example was `fn(&a)` and `fn(&X)`. In this case, `&a` will
be replaced with `$a` and we will ultimately compute a
(pre-replacement) GLB type of `fn($g)` where `$g=LUB($a,&X)`.
Therefore, `V={$a,$g}` and `Tainted($g)={$g,$a,&X}. To find the
replacement for `$g` we consult the rules above:
- Rule (1) does not apply because `$g \in V`
- Rule (2) does not apply because `&X \in Tainted($g)`
- Rule (3) does not apply because `$a \in Tainted($g)`
- Hence, by rule (4), we replace `$g` with a fresh bound variable `&z`.
So our final result is `fn(&z)`, which is correct.
The next example is `fn(&A)` and `fn(&Z)`. In this case, we will again
have a (pre-replacement) GLB of `fn(&g)`, where `$g = LUB(&A,&Z)`.
Therefore, `V={$g}` and `Tainted($g) = {$g, &A, &Z}`. In this case,
by rule (3), `$g` is mapped to itself, and hence the result is
`fn($g)`. This result is correct (in this case, at least), but it is
indicative of a case that *can* lead us into concluding that there is
no GLB when in fact a GLB does exist. See the section "Questionable
Results" below for more details.
The next example is `fn(&a, &b)` and `fn(&c, &c)`. In this case, as
before, we'll end up with `F=fn($g, $h)` where `Tainted($g) =
Tainted($h) = {$g, $h, $a, $b, $c}`. Only rule (4) applies and hence
we'll select fresh bound variables `y` and `z` and wind up with
`fn(&y, &z)`.
For the last example, let's consider what may seem trivial, but is
not: `fn(&a, &a)` and `fn(&b, &b)`. In this case, we'll get `F=fn($g,
$h)` where `Tainted($g) = {$g, $a, $x}` and `Tainted($h) = {$h, $a,
$x}`. Both of these sets contain exactly one bound variable from each
side, so we'll map them both to `&a`, resulting in `fn(&a, &a)`, which
is the desired result.
### Shortcomings and correctness
You may be wondering whether this algorithm is correct. The answer is
"sort of". There are definitely cases where they fail to compute a
result even though a correct result exists. I believe, though, that
if they succeed, then the result is valid, and I will attempt to
convince you. The basic argument is that the "pre-replacement" step
computes a set of constraints. The replacements, then, attempt to
satisfy those constraints, using bound identifiers where needed.
For now I will briefly go over the cases for LUB/GLB and identify
their intent:
- LUB:
- The region variables that are substituted in place of bound regions
are intended to collect constraints on those bound regions.
- If Tainted(R) contains only values in V, then this region is unconstrained
and can therefore be generalized, otherwise it cannot.
- GLB:
- The region variables that are substituted in place of bound regions
are intended to collect constraints on those bound regions.
- If Tainted(R) contains exactly one variable from each side, and
only variables in V, that indicates that those two bound regions
must be equated.
- Otherwise, if Tainted(R) references any variables from left or right
side, then it is trying to combine a bound region with a free one or
multiple bound regions, so we need to select fresh bound regions.
Sorry this is more of a shorthand to myself. I will try to write up something
more convincing in the future.
#### Where are the algorithms wrong?
- The pre-replacement computation can fail even though using a
bound-region would have succeeded.
- We will compute GLB(fn(fn($a)), fn(fn($b))) as fn($c) where $c is the
GLB of $a and $b. But if inference finds that $a and $b must be mapped
to regions without a GLB, then this is effectively a failure to compute
the GLB. However, the result `fn<$c>(fn($c))` is a valid GLB.
*/

984
src/librustc/middle/typeck/infer/region_inference.rs → src/librustc/middle/typeck/infer/region_inference/mod.rs
View File

File diff suppressed because it is too large Load Diff

13
src/librustc/middle/typeck/infer/sub.rs
View File

@ -20,6 +20,7 @@ use middle::typeck::infer::InferCtxt;
use middle::typeck::infer::lattice::CombineFieldsLatticeMethods;
use middle::typeck::infer::lub::Lub;
use middle::typeck::infer::to_str::InferStr;
use middle::typeck::infer::{TypeTrace, Subtype};
use util::common::{indent, indenter};
use util::ppaux::bound_region_to_str;
@ -36,7 +37,7 @@ impl Combine for Sub {
fn infcx(&self) -> @mut InferCtxt { self.infcx }
fn tag(&self) -> ~str { ~"sub" }
fn a_is_expected(&self) -> bool { self.a_is_expected }
fn span(&self) -> span { self.span }
fn trace(&self) -> TypeTrace { self.trace }
fn sub(&self) -> Sub { Sub(**self) }
fn lub(&self) -> Lub { Lub(**self) }
@ -62,12 +63,8 @@ impl Combine for Sub {
self.tag(),
a.inf_str(self.infcx),
b.inf_str(self.infcx));
do indent {
match self.infcx.region_vars.make_subregion(self.span, a, b) {
Ok(()) => Ok(a),
Err(ref e) => Err((*e))
}
}
self.infcx.region_vars.make_subregion(Subtype(self.trace), a, b);
Ok(a)
}
fn mts(&self, a: &ty::mt, b: &ty::mt) -> cres<ty::mt> {
@ -170,7 +167,7 @@ impl Combine for Sub {
// region variable.
let (a_sig, _) =
self.infcx.replace_bound_regions_with_fresh_regions(
self.span, a);
self.trace, a);
// Second, we instantiate each bound region in the supertype with a
// fresh concrete region.

2
src/librustc/middle/typeck/mod.rs
View File

@ -263,7 +263,7 @@ pub fn require_same_types(
}
}
match infer::mk_eqty(l_infcx, t1_is_expected, span, t1, t2) {
match infer::mk_eqty(l_infcx, t1_is_expected, infer::Misc(span), t1, t2) {
result::Ok(()) => true,
result::Err(ref terr) => {
l_tcx.sess.span_err(span, msg() + ": " +

19
src/librustc/util/ppaux.rs
View File

@ -608,6 +608,12 @@ impl Repr for @ast::pat {
}
}
impl Repr for ty::bound_region {
fn repr(&self, tcx: ctxt) -> ~str {
bound_region_ptr_to_str(tcx, *self)
}
}
impl Repr for ty::Region {
fn repr(&self, tcx: ctxt) -> ~str {
region_to_str(tcx, "", false, *self)
@ -793,6 +799,19 @@ impl Repr for ty::BuiltinBounds {
}
}
impl Repr for span {
fn repr(&self, tcx: ctxt) -> ~str {
tcx.sess.codemap.span_to_str(*self)
}
}
impl<A:UserString> UserString for @A {
fn user_string(&self, tcx: ctxt) -> ~str {
let this: &A = &**self;
this.user_string(tcx)
}
}
impl UserString for ty::BuiltinBounds {
fn user_string(&self, tcx: ctxt) -> ~str {
if self.is_empty() { ~"<no-bounds>" } else {

2
src/test/compile-fail/arc-rw-cond-shouldnt-escape.rs
View File

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// error-pattern: reference is not valid outside of its lifetime
// error-pattern: lifetime of return value does not outlive the function call
extern mod extra;
use extra::arc;
fn main() {

5
src/test/compile-fail/arc-rw-state-shouldnt-escape.rs
View File

@ -8,14 +8,15 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// error-pattern: reference is not valid outside of its lifetime
extern mod extra;
use extra::arc;
fn main() {
let x = ~arc::RWARC(1);
let mut y = None;
let mut y = None; //~ ERROR lifetime of variable does not enclose its declaration
do x.write |one| {
y = Some(one);
}
*y.unwrap() = 2;
//~^ ERROR lifetime of return value does not outlive the function call
//~^^ ERROR dereference of reference outside its lifetime
}

2
src/test/compile-fail/arc-rw-write-mode-cond-shouldnt-escape.rs
View File

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// error-pattern: reference is not valid outside of its lifetime
// error-pattern: lifetime of variable does not enclose its declaration
extern mod extra;
use extra::arc;
fn main() {

2
src/test/compile-fail/arc-rw-write-mode-shouldnt-escape.rs
View File

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// error-pattern: reference is not valid outside of its lifetime
// error-pattern: lifetime of variable does not enclose its declaration
extern mod extra;
use extra::arc;
fn main() {

4
src/test/compile-fail/borrowck-move-by-capture.rs
View File

@ -1,6 +1,4 @@
extern mod extra;
fn main() {
pub fn main() {
let foo = ~3;
let _pfoo = &foo;
let _f: @fn() -> int = || *foo + 5;

7
src/test/compile-fail/if-branch-types.rs
View File

@ -8,6 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// error-pattern:mismatched types
fn main() { let x = if true { 10i } else { 10u }; }
fn main() {
let x = if true { 10i } else { 10u };
//~^ ERROR if and else have incompatible types: expected `int` but found `uint`
}

10
src/test/compile-fail/kindck-owned-trait-contains.rs
View File

@ -23,13 +23,13 @@ fn main() {
// Error results because the type of is inferred to be
// @repeat<&'blk int> where blk is the lifetime of the block below.
let y = { //~ ERROR reference is not valid
let y = { //~ ERROR lifetime of variable does not enclose its declaration
let x: &'blk int = &3;
repeater(@x)
};
assert!(3 == *(y.get())); //~ ERROR dereference of reference outside its lifetime
//~^ ERROR reference is not valid outside of its lifetime
//~^^ ERROR reference is not valid outside of its lifetime
//~^^^ ERROR reference is not valid outside of its lifetime
assert!(3 == *(y.get()));
//~^ ERROR dereference of reference outside its lifetime
//~^^ ERROR automatically borrowed pointer is not valid at the time of borrow
//~^^^ ERROR lifetime of return value does not outlive the function call
//~^^^^ ERROR cannot infer an appropriate lifetime
}

52
src/test/compile-fail/lub-if.rs Normal file
View File

@ -0,0 +1,52 @@
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// Test that we correctly consider the type of `match` to be the LUB
// of the various arms, particularly in the case where regions are
// involved.
pub fn opt_str0<'a>(maybestr: &'a Option<~str>) -> &'a str {
if maybestr.is_none() {
"(none)"
} else {
let s: &'a str = *maybestr.get_ref();
s
}
}
pub fn opt_str1<'a>(maybestr: &'a Option<~str>) -> &'a str {
if maybestr.is_some() {
let s: &'a str = *maybestr.get_ref();
s
} else {
"(none)"
}
}
pub fn opt_str2<'a>(maybestr: &'a Option<~str>) -> &'static str {
if maybestr.is_none() { //~ ERROR mismatched types
"(none)"
} else {
let s: &'a str = *maybestr.get_ref();
s
}
}
pub fn opt_str3<'a>(maybestr: &'a Option<~str>) -> &'static str {
if maybestr.is_some() { //~ ERROR mismatched types
let s: &'a str = *maybestr.get_ref();
s
} else {
"(none)"
}
}
fn main() {}

55
src/test/compile-fail/lub-match.rs Normal file
View File

@ -0,0 +1,55 @@
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// Test that we correctly consider the type of `match` to be the LUB
// of the various arms, particularly in the case where regions are
// involved.
pub fn opt_str0<'a>(maybestr: &'a Option<~str>) -> &'a str {
match *maybestr {
Some(ref s) => {
let s: &'a str = *s;
s
}
None => "(none)",
}
}
pub fn opt_str1<'a>(maybestr: &'a Option<~str>) -> &'a str {
match *maybestr {
None => "(none)",
Some(ref s) => {
let s: &'a str = *s;
s
}
}
}
pub fn opt_str2<'a>(maybestr: &'a Option<~str>) -> &'static str {
match *maybestr { //~ ERROR mismatched types
None => "(none)",
Some(ref s) => {
let s: &'a str = *s;
s
}
}
}
pub fn opt_str3<'a>(maybestr: &'a Option<~str>) -> &'static str {
match *maybestr { //~ ERROR mismatched types
Some(ref s) => {
let s: &'a str = *s;
s
}
None => "(none)",
}
}
fn main() {}

2
src/test/compile-fail/regions-bounds.rs
View File

@ -17,10 +17,12 @@ struct a_class<'self> { x:&'self int }
fn a_fn1<'a,'b>(e: an_enum<'a>) -> an_enum<'b> {
return e; //~ ERROR mismatched types: expected `an_enum<'b>` but found `an_enum<'a>`
//~^ ERROR cannot infer an appropriate lifetime
}
fn a_fn3<'a,'b>(e: a_class<'a>) -> a_class<'b> {
return e; //~ ERROR mismatched types: expected `a_class<'b>` but found `a_class<'a>`
//~^ ERROR cannot infer an appropriate lifetime
}
fn a_fn4<'a,'b>() {

2
src/test/compile-fail/regions-escape-bound-fn-2.rs
View File

@ -15,6 +15,6 @@ fn with_int(f: &fn(x: &int)) {
fn main() {
let mut x = None;
//~^ ERROR reference is not valid outside of its lifetime
//~^ ERROR lifetime of variable does not enclose its declaration
with_int(|y| x = Some(y));
}

2
src/test/compile-fail/regions-escape-via-trait-or-not.rs
View File

@ -23,7 +23,7 @@ fn with<R:deref>(f: &fn(x: &int) -> R) -> int {
}
fn return_it() -> int {
with(|o| o) //~ ERROR reference is not valid outside of its lifetime
with(|o| o) //~ ERROR lifetime of function argument does not outlive the function call
}
fn main() {

11
src/test/run-pass/issue-4325.rs → src/test/compile-fail/regions-free-region-ordering-incorrect.rs
View File

@ -8,16 +8,23 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// Test that free regions ordering only goes one way. That is,
// we have `&'a Node<'self, T>`, which implies that `'a <= 'self`,
// but not `'self <= 'a`. Hence returning `&self.val` (which has lifetime
// `'a`) where `'self` is expected yields an error.
//
// This test began its life as a test for issue #4325.
struct Node<'self, T> {
val: T,
next: Option<&'self Node<'self, T>>
}
impl<'self, T> Node<'self, T> {
fn get(&self) -> &'self T {
fn get<'a>(&'a self) -> &'self T {
match self.next {
Some(ref next) => next.get(),
None => &self.val
None => &self.val //~ ERROR cannot infer an appropriate lifetime
}
}
}

5
src/test/compile-fail/regions-infer-at-fn-not-param.rs
View File

@ -20,7 +20,10 @@ struct not_parameterized2 {
g: @fn()
}
fn take1(p: parameterized1) -> parameterized1 { p } //~ ERROR mismatched types
fn take1(p: parameterized1) -> parameterized1 { p }
//~^ ERROR mismatched types
//~^^ ERROR cannot infer an appropriate lifetime
fn take3(p: not_parameterized1) -> not_parameterized1 { p }
fn take4(p: not_parameterized2) -> not_parameterized2 { p }

1
src/test/compile-fail/regions-infer-covariance-due-to-arg.rs
View File

@ -22,6 +22,7 @@ fn to_same_lifetime<'r>(bi: covariant<'r>) {
fn to_shorter_lifetime<'r>(bi: covariant<'r>) {
let bj: covariant<'blk> = bi; //~ ERROR mismatched types
//~^ ERROR cannot infer an appropriate lifetime
}
fn to_longer_lifetime<'r>(bi: covariant<'r>) -> covariant<'static> {

5
src/test/compile-fail/regions-infer-not-param.rs
View File

@ -23,6 +23,11 @@ struct indirect2<'self> {
}
fn take_direct(p: direct) -> direct { p } //~ ERROR mismatched types
//~^ ERROR cannot infer an appropriate lifetime
fn take_indirect1(p: indirect1) -> indirect1 { p }
fn take_indirect2(p: indirect2) -> indirect2 { p } //~ ERROR mismatched types
//~^ ERROR cannot infer an appropriate lifetime
fn main() {}

1
src/test/compile-fail/regions-infer-paramd-indirect.rs
View File

@ -30,6 +30,7 @@ impl<'self> set_f<'self> for c<'self> {
fn set_f_bad(&self, b: @b) {
self.f = b; //~ ERROR mismatched types: expected `@@&'self int` but found `@@&int`
//~^ ERROR cannot infer an appropriate lifetime
}
}

1
src/test/compile-fail/regions-nested-fns.rs
View File

@ -22,6 +22,7 @@ fn nested<'x>(x: &'x int) {
ignore::<&fn<'z>(&'z int) -> &'z int>(|z| {
if false { return x; } //~ ERROR mismatched types
//~^ ERROR cannot infer an appropriate lifetime
if false { return ay; }
return z;
});

2
src/test/compile-fail/regions-ret-borrowed-1.rs
View File

@ -18,6 +18,8 @@ fn with<'a, R>(f: &fn(x: &'a int) -> R) -> R {
fn return_it<'a>() -> &'a int {
with(|o| o) //~ ERROR mismatched types
//~^ ERROR lifetime of return value does not outlive the function call
//~^^ ERROR cannot infer an appropriate lifetime
}
fn main() {

2
src/test/compile-fail/regions-ret-borrowed.rs
View File

@ -21,6 +21,8 @@ fn with<R>(f: &fn(x: &int) -> R) -> R {
fn return_it() -> &int {
with(|o| o) //~ ERROR mismatched types
//~^ ERROR lifetime of return value does not outlive the function call
//~^^ ERROR cannot infer an appropriate lifetime
}
fn main() {

2
src/test/compile-fail/sync-cond-shouldnt-escape.rs
View File

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// error-pattern: reference is not valid outside of its lifetime
// error-pattern: lifetime of variable does not enclose its declaration
extern mod extra;
use extra::sync;

2
src/test/compile-fail/sync-rwlock-cond-shouldnt-escape.rs
View File

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// error-pattern: reference is not valid outside of its lifetime
// error-pattern: lifetime of method receiver does not outlive the method call
extern mod extra;
use extra::sync;
fn main() {

2
src/test/compile-fail/sync-rwlock-write-mode-cond-shouldnt-escape.rs
View File

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// error-pattern: reference is not valid outside of its lifetime
// error-pattern: lifetime of variable does not enclose its declaration
extern mod extra;
use extra::sync;
fn main() {

2
src/test/compile-fail/sync-rwlock-write-mode-shouldnt-escape.rs
View File

@ -8,7 +8,7 @@
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// error-pattern: reference is not valid outside of its lifetime
// error-pattern: lifetime of variable does not enclose its declaration
extern mod extra;
use extra::sync;
fn main() {