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fallback to provided signature in the event of a type error

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This prevents regressions on some annoying cases.
This commit is contained in:
Niko Matsakis 2017-11-02 17:24:44 -04:00
parent 053383dbef
commit e8a96c97f4
4 changed files with 249 additions and 176 deletions
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398
src/librustc_typeck/check/closure.rs
View File

@ -14,6 +14,7 @@ use super::{check_fn, Expectation, FnCtxt};
use astconv::AstConv;
use rustc::hir::def_id::DefId;
use rustc::infer::{InferOk, InferResult};
use rustc::infer::LateBoundRegionConversionTime;
use rustc::infer::type_variable::TypeVariableOrigin;
use rustc::ty::{self, ToPolyTraitRef, Ty};
@ -30,16 +31,19 @@ struct ClosureSignatures<'tcx> {
}
impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
pub fn check_expr_closure(&self,
expr: &hir::Expr,
_capture: hir::CaptureClause,
decl: &'gcx hir::FnDecl,
body_id: hir::BodyId,
expected: Expectation<'tcx>)
-> Ty<'tcx> {
debug!("check_expr_closure(expr={:?},expected={:?})",
expr,
expected);
pub fn check_expr_closure(
&self,
expr: &hir::Expr,
_capture: hir::CaptureClause,
decl: &'gcx hir::FnDecl,
body_id: hir::BodyId,
expected: Expectation<'tcx>,
) -> Ty<'tcx> {
debug!(
"check_expr_closure(expr={:?},expected={:?})",
expr,
expected
);
// It's always helpful for inference if we know the kind of
// closure sooner rather than later, so first examine the expected
@ -52,60 +56,84 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
self.check_closure(expr, expected_kind, decl, body, expected_sig)
}
fn check_closure(&self,
expr: &hir::Expr,
opt_kind: Option<ty::ClosureKind>,
decl: &'gcx hir::FnDecl,
body: &'gcx hir::Body,
expected_sig: Option<ty::FnSig<'tcx>>)
-> Ty<'tcx> {
debug!("check_closure(opt_kind={:?}, expected_sig={:?})",
opt_kind,
expected_sig);
fn check_closure(
&self,
expr: &hir::Expr,
opt_kind: Option<ty::ClosureKind>,
decl: &'gcx hir::FnDecl,
body: &'gcx hir::Body,
expected_sig: Option<ty::FnSig<'tcx>>,
) -> Ty<'tcx> {
debug!(
"check_closure(opt_kind={:?}, expected_sig={:?})",
opt_kind,
expected_sig
);
let expr_def_id = self.tcx.hir.local_def_id(expr.id);
let ClosureSignatures { bound_sig, liberated_sig } =
self.sig_of_closure(expr_def_id, decl, body, expected_sig);
let ClosureSignatures {
bound_sig,
liberated_sig,
} = self.sig_of_closure(expr_def_id, decl, body, expected_sig);
debug!("check_closure: ty_of_closure returns {:?}", liberated_sig);
let interior = check_fn(self, self.param_env, liberated_sig, decl, expr.id, body, true).1;
let interior = check_fn(
self,
self.param_env,
liberated_sig,
decl,
expr.id,
body,
true,
).1;
// Create type variables (for now) to represent the transformed
// types of upvars. These will be unified during the upvar
// inference phase (`upvar.rs`).
let base_substs = Substs::identity_for_item(self.tcx,
self.tcx.closure_base_def_id(expr_def_id));
let substs = base_substs.extend_to(self.tcx, expr_def_id,
|_, _| span_bug!(expr.span, "closure has region param"),
|_, _| self.infcx.next_ty_var(TypeVariableOrigin::TransformedUpvar(expr.span))
let base_substs =
Substs::identity_for_item(self.tcx, self.tcx.closure_base_def_id(expr_def_id));
let substs = base_substs.extend_to(
self.tcx,
expr_def_id,
|_, _| span_bug!(expr.span, "closure has region param"),
|_, _| {
self.infcx
.next_ty_var(TypeVariableOrigin::TransformedUpvar(expr.span))
},
);
let closure_type = self.tcx.mk_closure(expr_def_id, substs);
if let Some(interior) = interior {
let closure_substs = ty::ClosureSubsts {
substs: substs,
};
let closure_substs = ty::ClosureSubsts { substs: substs };
return self.tcx.mk_generator(expr_def_id, closure_substs, interior);
}
debug!("check_closure: expr.id={:?} closure_type={:?}", expr.id, closure_type);
debug!(
"check_closure: expr.id={:?} closure_type={:?}",
expr.id,
closure_type
);
// Tuple up the arguments and insert the resulting function type into
// the `closures` table.
let sig = bound_sig.map_bound(|sig| self.tcx.mk_fn_sig(
iter::once(self.tcx.intern_tup(sig.inputs(), false)),
sig.output(),
sig.variadic,
sig.unsafety,
sig.abi
));
let sig = bound_sig.map_bound(|sig| {
self.tcx.mk_fn_sig(
iter::once(self.tcx.intern_tup(sig.inputs(), false)),
sig.output(),
sig.variadic,
sig.unsafety,
sig.abi,
)
});
debug!("check_closure: expr_def_id={:?}, sig={:?}, opt_kind={:?}",
expr_def_id,
sig,
opt_kind);
debug!(
"check_closure: expr_def_id={:?}, sig={:?}, opt_kind={:?}",
expr_def_id,
sig,
opt_kind
);
{
let mut tables = self.tables.borrow_mut();
@ -121,22 +149,26 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
closure_type
}
fn deduce_expectations_from_expected_type
(&self,
expected_ty: Ty<'tcx>)
-> (Option<ty::FnSig<'tcx>>, Option<ty::ClosureKind>) {
debug!("deduce_expectations_from_expected_type(expected_ty={:?})",
expected_ty);
fn deduce_expectations_from_expected_type(
&self,
expected_ty: Ty<'tcx>,
) -> (Option<ty::FnSig<'tcx>>, Option<ty::ClosureKind>) {
debug!(
"deduce_expectations_from_expected_type(expected_ty={:?})",
expected_ty
);
match expected_ty.sty {
ty::TyDynamic(ref object_type, ..) => {
let sig = object_type.projection_bounds()
let sig = object_type
.projection_bounds()
.filter_map(|pb| {
let pb = pb.with_self_ty(self.tcx, self.tcx.types.err);
self.deduce_sig_from_projection(&pb)
})
.next();
let kind = object_type.principal()
let kind = object_type
.principal()
.and_then(|p| self.tcx.lang_items().fn_trait_kind(p.def_id()));
(sig, kind)
}
@ -146,19 +178,22 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
}
}
fn deduce_expectations_from_obligations
(&self,
expected_vid: ty::TyVid)
-> (Option<ty::FnSig<'tcx>>, Option<ty::ClosureKind>) {
fn deduce_expectations_from_obligations(
&self,
expected_vid: ty::TyVid,
) -> (Option<ty::FnSig<'tcx>>, Option<ty::ClosureKind>) {
let fulfillment_cx = self.fulfillment_cx.borrow();
// Here `expected_ty` is known to be a type inference variable.
let expected_sig = fulfillment_cx.pending_obligations()
let expected_sig = fulfillment_cx
.pending_obligations()
.iter()
.map(|obligation| &obligation.obligation)
.filter_map(|obligation| {
debug!("deduce_expectations_from_obligations: obligation.predicate={:?}",
obligation.predicate);
debug!(
"deduce_expectations_from_obligations: obligation.predicate={:?}",
obligation.predicate
);
match obligation.predicate {
// Given a Projection predicate, we can potentially infer
@ -177,7 +212,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
// infer the kind. This can occur if there is a trait-reference
// like `F : Fn<A>`. Note that due to subtyping we could encounter
// many viable options, so pick the most restrictive.
let expected_kind = fulfillment_cx.pending_obligations()
let expected_kind = fulfillment_cx
.pending_obligations()
.iter()
.map(|obligation| &obligation.obligation)
.filter_map(|obligation| {
@ -202,20 +238,23 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
// inference variable.
ty::Predicate::ClosureKind(..) => None,
};
opt_trait_ref.and_then(|tr| self.self_type_matches_expected_vid(tr, expected_vid))
opt_trait_ref
.and_then(|tr| self.self_type_matches_expected_vid(tr, expected_vid))
.and_then(|tr| self.tcx.lang_items().fn_trait_kind(tr.def_id()))
})
.fold(None,
|best, cur| Some(best.map_or(cur, |best| cmp::min(best, cur))));
.fold(None, |best, cur| {
Some(best.map_or(cur, |best| cmp::min(best, cur)))
});
(expected_sig, expected_kind)
}
/// Given a projection like "<F as Fn(X)>::Result == Y", we can deduce
/// everything we need to know about a closure.
fn deduce_sig_from_projection(&self,
projection: &ty::PolyProjectionPredicate<'tcx>)
-> Option<ty::FnSig<'tcx>> {
fn deduce_sig_from_projection(
&self,
projection: &ty::PolyProjectionPredicate<'tcx>,
) -> Option<ty::FnSig<'tcx>> {
let tcx = self.tcx;
debug!("deduce_sig_from_projection({:?})", projection);
@ -228,8 +267,10 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
let arg_param_ty = trait_ref.substs().type_at(1);
let arg_param_ty = self.resolve_type_vars_if_possible(&arg_param_ty);
debug!("deduce_sig_from_projection: arg_param_ty {:?}",
arg_param_ty);
debug!(
"deduce_sig_from_projection: arg_param_ty {:?}",
arg_param_ty
);
let input_tys = match arg_param_ty.sty {
ty::TyTuple(tys, _) => tys.into_iter(),
@ -240,41 +281,47 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
let ret_param_ty = projection.0.ty;
let ret_param_ty = self.resolve_type_vars_if_possible(&ret_param_ty);
debug!("deduce_sig_from_projection: ret_param_ty {:?}", ret_param_ty);
debug!(
"deduce_sig_from_projection: ret_param_ty {:?}",
ret_param_ty
);
let fn_sig = self.tcx.mk_fn_sig(
input_tys.cloned(),
ret_param_ty,
false,
hir::Unsafety::Normal,
Abi::Rust
Abi::Rust,
);
debug!("deduce_sig_from_projection: fn_sig {:?}", fn_sig);
Some(fn_sig)
}
fn self_type_matches_expected_vid(&self,
trait_ref: ty::PolyTraitRef<'tcx>,
expected_vid: ty::TyVid)
-> Option<ty::PolyTraitRef<'tcx>> {
fn self_type_matches_expected_vid(
&self,
trait_ref: ty::PolyTraitRef<'tcx>,
expected_vid: ty::TyVid,
) -> Option<ty::PolyTraitRef<'tcx>> {
let self_ty = self.shallow_resolve(trait_ref.self_ty());
debug!("self_type_matches_expected_vid(trait_ref={:?}, self_ty={:?})",
trait_ref,
self_ty);
debug!(
"self_type_matches_expected_vid(trait_ref={:?}, self_ty={:?})",
trait_ref,
self_ty
);
match self_ty.sty {
ty::TyInfer(ty::TyVar(v)) if expected_vid == v => Some(trait_ref),
_ => None,
}
}
fn sig_of_closure(&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
body: &hir::Body,
expected_sig: Option<ty::FnSig<'tcx>>)
-> ClosureSignatures<'tcx>
{
fn sig_of_closure(
&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
body: &hir::Body,
expected_sig: Option<ty::FnSig<'tcx>>,
) -> ClosureSignatures<'tcx> {
if let Some(e) = expected_sig {
self.sig_of_closure_with_expectation(expr_def_id, decl, body, e)
} else {
@ -284,12 +331,12 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
/// If there is no expected signature, then we will convert the
/// types that the user gave into a signature.
fn sig_of_closure_no_expectation(&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
body: &hir::Body)
-> ClosureSignatures<'tcx>
{
fn sig_of_closure_no_expectation(
&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
body: &hir::Body,
) -> ClosureSignatures<'tcx> {
debug!("sig_of_closure_no_expectation()");
let bound_sig = self.supplied_sig_of_closure(decl);
@ -344,14 +391,17 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
/// - `expected_sig`: the expected signature (if any). Note that
/// this is missing a binder: that is, there may be late-bound
/// regions with depth 1, which are bound then by the closure.
fn sig_of_closure_with_expectation(&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
body: &hir::Body,
expected_sig: ty::FnSig<'tcx>)
-> ClosureSignatures<'tcx>
{
debug!("sig_of_closure_with_expectation(expected_sig={:?})", expected_sig);
fn sig_of_closure_with_expectation(
&self,
expr_def_id: DefId,
decl: &hir::FnDecl,
body: &hir::Body,
expected_sig: ty::FnSig<'tcx>,
) -> ClosureSignatures<'tcx> {
debug!(
"sig_of_closure_with_expectation(expected_sig={:?})",
expected_sig
);
// Watch out for some surprises and just ignore the
// expectation if things don't see to match up with what we
@ -367,13 +417,13 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
// regions appearing free in `expected_sig` are now bound up
// in this binder we are creating.
assert!(!expected_sig.has_regions_escaping_depth(1));
let bound_sig =
ty::Binder(self.tcx.mk_fn_sig(
expected_sig.inputs().iter().cloned(),
expected_sig.output(),
decl.variadic,
hir::Unsafety::Normal,
Abi::RustCall));
let bound_sig = ty::Binder(self.tcx.mk_fn_sig(
expected_sig.inputs().iter().cloned(),
expected_sig.output(),
decl.variadic,
hir::Unsafety::Normal,
Abi::RustCall,
));
// `deduce_expectations_from_expected_type` introduces
// late-bound lifetimes defined elsewhere, which we now
@ -387,7 +437,10 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
// Along the way, it also writes out entries for types that the user
// wrote into our tables, which are then later used by the privacy
// check.
self.check_supplied_sig_against_expectation(decl, &closure_sigs);
match self.check_supplied_sig_against_expectation(decl, &closure_sigs) {
Ok(infer_ok) => self.register_infer_ok_obligations(infer_ok),
Err(_) => return self.sig_of_closure_no_expectation(expr_def_id, decl, body),
}
closure_sigs
}
@ -395,58 +448,90 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
/// Enforce the user's types against the expectation. See
/// `sig_of_closure_with_expectation` for details on the overall
/// strategy.
fn check_supplied_sig_against_expectation(&self,
decl: &hir::FnDecl,
expected_sigs: &ClosureSignatures<'tcx>)
{
fn check_supplied_sig_against_expectation(
&self,
decl: &hir::FnDecl,
expected_sigs: &ClosureSignatures<'tcx>,
) -> InferResult<'tcx, ()> {
// Get the signature S that the user gave.
//
// (See comment on `sig_of_closure_with_expectation` for the
// meaning of these letters.)
let supplied_sig = self.supplied_sig_of_closure(decl);
debug!("check_supplied_sig_against_expectation: supplied_sig={:?}",
supplied_sig);
debug!(
"check_supplied_sig_against_expectation: supplied_sig={:?}",
supplied_sig
);
// The liberated version of this signature should be be a subtype
// of the liberated form of the expectation.
for ((hir_ty, &supplied_ty), expected_ty) in
decl.inputs.iter()
.zip(*supplied_sig.inputs().skip_binder()) // binder moved to (*) below
.zip(expected_sigs.liberated_sig.inputs()) // `liberated_sig` is E'.
{
// Instantiate (this part of..) S to S', i.e., with fresh variables.
let (supplied_ty, _) = self.infcx.replace_late_bound_regions_with_fresh_var(
hir_ty.span,
// FIXME(#45727): As discussed in [this comment][c1], naively
// forcing equality here actually results in suboptimal error
// messages in some cases. For now, if there would have been
// an obvious error, we fallback to declaring the type of the
// closure to be the one the user gave, which allows other
// error message code to trigger.
//
// However, I think [there is potential to do even better
// here][c2], since in *this* code we have the precise span of
// the type parameter in question in hand when we report the
// error.
//
// [c1]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341089706
// [c2]: https://github.com/rust-lang/rust/pull/45072#issuecomment-341096796
self.infcx.commit_if_ok(|_| {
let mut all_obligations = vec![];
// The liberated version of this signature should be be a subtype
// of the liberated form of the expectation.
for ((hir_ty, &supplied_ty), expected_ty) in decl.inputs.iter()
.zip(*supplied_sig.inputs().skip_binder()) // binder moved to (*) below
.zip(expected_sigs.liberated_sig.inputs())
// `liberated_sig` is E'.
{
// Instantiate (this part of..) S to S', i.e., with fresh variables.
let (supplied_ty, _) = self.infcx.replace_late_bound_regions_with_fresh_var(
hir_ty.span,
LateBoundRegionConversionTime::FnCall,
&ty::Binder(supplied_ty),
); // recreated from (*) above
// Check that E' = S'.
let cause = &self.misc(hir_ty.span);
let InferOk {
value: (),
obligations,
} = self.at(cause, self.param_env)
.eq(*expected_ty, supplied_ty)?;
all_obligations.extend(obligations);
}
let (supplied_output_ty, _) = self.infcx.replace_late_bound_regions_with_fresh_var(
decl.output.span(),
LateBoundRegionConversionTime::FnCall,
&ty::Binder(supplied_ty)); // recreated from (*) above
&supplied_sig.output(),
);
let cause = &self.misc(decl.output.span());
let InferOk {
value: (),
obligations,
} = self.at(cause, self.param_env)
.eq(expected_sigs.liberated_sig.output(), supplied_output_ty)?;
all_obligations.extend(obligations);
// Check that E' = S'.
self.demand_eqtype(hir_ty.span, expected_ty, supplied_ty);
}
let (supplied_output_ty, _) = self.infcx.replace_late_bound_regions_with_fresh_var(
decl.output.span(),
LateBoundRegionConversionTime::FnCall,
&supplied_sig.output());
self.demand_eqtype(decl.output.span(),
expected_sigs.liberated_sig.output(),
supplied_output_ty);
Ok(InferOk {
value: (),
obligations: all_obligations,
})
})
}
/// If there is no expected signature, then we will convert the
/// types that the user gave into a signature.
fn supplied_sig_of_closure(&self,
decl: &hir::FnDecl)
-> ty::PolyFnSig<'tcx>
{
fn supplied_sig_of_closure(&self, decl: &hir::FnDecl) -> ty::PolyFnSig<'tcx> {
let astconv: &AstConv = self;
// First, convert the types that the user supplied (if any).
let supplied_arguments =
decl.inputs
.iter()
.map(|a| astconv.ast_ty_to_ty(a));
let supplied_arguments = decl.inputs.iter().map(|a| astconv.ast_ty_to_ty(a));
let supplied_return = match decl.output {
hir::Return(ref output) => astconv.ast_ty_to_ty(&output),
hir::DefaultReturn(_) => astconv.ty_infer(decl.output.span()),
@ -457,25 +542,30 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
supplied_return,
decl.variadic,
hir::Unsafety::Normal,
Abi::RustCall));
Abi::RustCall,
));
debug!("supplied_sig_of_closure: result={:?}", result);
result
}
fn closure_sigs(&self,
expr_def_id: DefId,
body: &hir::Body,
bound_sig: ty::PolyFnSig<'tcx>)
-> ClosureSignatures<'tcx>
{
fn closure_sigs(
&self,
expr_def_id: DefId,
body: &hir::Body,
bound_sig: ty::PolyFnSig<'tcx>,
) -> ClosureSignatures<'tcx> {
let liberated_sig = self.liberate_late_bound_regions(expr_def_id, &bound_sig);
let liberated_sig = self.inh.normalize_associated_types_in(body.value.span,
body.value.id,
self.param_env,
&liberated_sig);
ClosureSignatures { bound_sig, liberated_sig }
let liberated_sig = self.inh.normalize_associated_types_in(
body.value.span,
body.value.id,
self.param_env,
&liberated_sig,
);
ClosureSignatures {
bound_sig,
liberated_sig,
}
}
}

6
src/test/compile-fail/closure-expected-type/expect-fn-supply-fn.rs
View File

@ -40,14 +40,14 @@ fn expect_free_supply_bound() {
// Here, we are given a function whose region is bound at closure level,
// but we expect one bound in the argument. Error results.
with_closure_expecting_fn_with_free_region(|x: fn(&u32), y| {});
//~^ ERROR mismatched types
//~^ ERROR type mismatch in closure arguments
}
fn expect_bound_supply_free_from_fn<'x>(x: &'x u32) {
// Here, we are given a `fn(&u32)` but we expect a `fn(&'x
// u32)`. In principle, this could be ok, but we demand equality.
with_closure_expecting_fn_with_bound_region(|x: fn(&'x u32), y| {});
//~^ ERROR mismatched types
//~^ ERROR type mismatch in closure arguments
}
fn expect_bound_supply_free_from_closure() {
@ -56,7 +56,7 @@ fn expect_bound_supply_free_from_closure() {
// the argument level.
type Foo<'a> = fn(&'a u32);
with_closure_expecting_fn_with_bound_region(|_x: Foo<'_>, y| {});
//~^ ERROR mismatched types
//~^ ERROR type mismatch in closure arguments
}
fn expect_bound_supply_bound<'x>(x: &'x u32) {

2
src/test/compile-fail/closure-expected-type/expect-infer-var-appearing-twice.rs
View File

@ -22,7 +22,7 @@ fn a() {
fn b() {
// Here we take the supplied types, resulting in an error later on.
with_closure(|x: u32, y: i32| {
//~^ ERROR mismatched types
//~^ ERROR type mismatch in closure arguments
});
}

19
src/test/ui/mismatched_types/closure-arg-count.stderr
View File

@ -14,23 +14,6 @@ error[E0593]: closure is expected to take 2 arguments, but it takes 1 argument
| |
| expected closure that takes 2 arguments
error: non-reference pattern used to match a reference (see issue #42640)
--> $DIR/closure-arg-count.rs:17:24
|
17 | [1, 2, 3].sort_by(|(tuple, tuple2)| panic!());
| ^^^^^^^^^^^^^^^ help: consider using: `&(tuple, tuple2)`
|
= help: add #![feature(match_default_bindings)] to the crate attributes to enable
error[E0308]: mismatched types
--> $DIR/closure-arg-count.rs:17:24
|
17 | [1, 2, 3].sort_by(|(tuple, tuple2)| panic!());
| ^^^^^^^^^^^^^^^ expected integral variable, found tuple
|
= note: expected type `{integer}`
found type `(_, _)`
error[E0593]: closure is expected to take 2 arguments, but it takes 1 argument
--> $DIR/closure-arg-count.rs:17:15
|
@ -73,5 +56,5 @@ error[E0593]: closure is expected to take a single 2-tuple as argument, but it t
| |
| expected closure that takes a single 2-tuple as argument
error: aborting due to 9 previous errors
error: aborting due to 7 previous errors