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Enable migrate mode by default on the 2015 edition

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This also fully stabilizes two-phase borrows on all editions
This commit is contained in:
Matthew Jasper 2019-01-26 17:25:37 +00:00
parent 31a75a1728
commit aa6fb6caf9
16 changed files with 154 additions and 357 deletions
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4
src/librustc/infer/mod.rs
View File

@ -92,8 +92,8 @@ impl SuppressRegionErrors {
/// enabled.
pub fn when_nll_is_enabled(tcx: TyCtxt<'_, '_, '_>) -> Self {
match tcx.borrowck_mode() {
// If we're on AST or Migrate mode, report AST region errors
BorrowckMode::Ast | BorrowckMode::Migrate => SuppressRegionErrors { suppressed: false },
// If we're on Migrate mode, report AST region errors
BorrowckMode::Migrate => SuppressRegionErrors { suppressed: false },
// If we're on MIR or Compare mode, don't report AST region errors as they should
// be reported by NLL

17
src/librustc/session/config.rs
View File

@ -460,7 +460,6 @@ pub enum PrintRequest {
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum BorrowckMode {
Ast,
Mir,
Compare,
Migrate,
@ -471,7 +470,6 @@ impl BorrowckMode {
/// on the AST borrow check if the MIR-based one errors.
pub fn migrate(self) -> bool {
match self {
BorrowckMode::Ast => false,
BorrowckMode::Compare => false,
BorrowckMode::Mir => false,
BorrowckMode::Migrate => true,
@ -481,21 +479,11 @@ impl BorrowckMode {
/// Should we emit the AST-based borrow checker errors?
pub fn use_ast(self) -> bool {
match self {
BorrowckMode::Ast => true,
BorrowckMode::Compare => true,
BorrowckMode::Mir => false,
BorrowckMode::Migrate => false,
}
}
/// Should we emit the MIR-based borrow checker errors?
pub fn use_mir(self) -> bool {
match self {
BorrowckMode::Ast => false,
BorrowckMode::Compare => true,
BorrowckMode::Mir => true,
BorrowckMode::Migrate => true,
}
}
}
pub enum Input {
@ -627,7 +615,7 @@ impl Default for Options {
incremental: None,
debugging_opts: basic_debugging_options(),
prints: Vec::new(),
borrowck_mode: BorrowckMode::Ast,
borrowck_mode: BorrowckMode::Migrate,
cg: basic_codegen_options(),
error_format: ErrorOutputType::default(),
externs: Externs(BTreeMap::new()),
@ -2326,10 +2314,9 @@ pub fn build_session_options_and_crate_config(
}));
let borrowck_mode = match debugging_opts.borrowck.as_ref().map(|s| &s[..]) {
None | Some("ast") => BorrowckMode::Ast,
None | Some("migrate") => BorrowckMode::Migrate,
Some("mir") => BorrowckMode::Mir,
Some("compare") => BorrowckMode::Compare,
Some("migrate") => BorrowckMode::Migrate,
Some(m) => early_error(error_format, &format!("unknown borrowck mode `{}`", m)),
};

60
src/librustc/ty/context.rs
View File

@ -70,7 +70,6 @@ use rustc_macros::HashStable;
use syntax::ast;
use syntax::attr;
use syntax::source_map::MultiSpan;
use syntax::edition::Edition;
use syntax::feature_gate;
use syntax::symbol::{Symbol, keywords, InternedString};
use syntax_pos::Span;
@ -1496,21 +1495,13 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
/// because that method has a narrower effect that can be toggled
/// off via a separate `-Z` flag, at least for the short term.
pub fn allow_bind_by_move_patterns_with_guards(self) -> bool {
self.features().bind_by_move_pattern_guards && self.use_mir_borrowck()
self.features().bind_by_move_pattern_guards
}
/// If true, we should use a naive AST walk to determine if match
/// guard could perform bad mutations (or mutable-borrows).
pub fn check_for_mutation_in_guard_via_ast_walk(self) -> bool {
// If someone requests the feature, then be a little more
// careful and ensure that MIR-borrowck is enabled (which can
// happen via edition selection, via `feature(nll)`, or via an
// appropriate `-Z` flag) before disabling the mutation check.
if self.allow_bind_by_move_patterns_with_guards() {
return false;
}
return true;
!self.allow_bind_by_move_patterns_with_guards()
}
/// If true, we should use the AST-based borrowck (we may *also* use
@ -1519,12 +1510,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
self.borrowck_mode().use_ast()
}
/// If true, we should use the MIR-based borrowck (we may *also* use
/// the AST-based borrowck).
pub fn use_mir_borrowck(self) -> bool {
self.borrowck_mode().use_mir()
}
/// If true, we should use the MIR-based borrow check, but also
/// fall back on the AST borrow check if the MIR-based one errors.
pub fn migrate_borrowck(self) -> bool {
@ -1541,23 +1526,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
/// statements (which simulate the maximal effect of executing the
/// patterns in a match arm).
pub fn emit_read_for_match(&self) -> bool {
self.use_mir_borrowck() && !self.sess.opts.debugging_opts.nll_dont_emit_read_for_match
}
/// If true, pattern variables for use in guards on match arms
/// will be bound as references to the data, and occurrences of
/// those variables in the guard expression will implicitly
/// dereference those bindings. (See rust-lang/rust#27282.)
pub fn all_pat_vars_are_implicit_refs_within_guards(self) -> bool {
self.borrowck_mode().use_mir()
}
/// If true, we should enable two-phase borrows checks. This is
/// done with either: `-Ztwo-phase-borrows`, `#![feature(nll)]`,
/// or by opting into an edition after 2015.
pub fn two_phase_borrows(self) -> bool {
self.sess.rust_2018() || self.features().nll ||
self.sess.opts.debugging_opts.two_phase_borrows
!self.sess.opts.debugging_opts.nll_dont_emit_read_for_match
}
/// What mode(s) of borrowck should we run? AST? MIR? both?
@ -1565,14 +1534,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
pub fn borrowck_mode(&self) -> BorrowckMode {
// Here are the main constraints we need to deal with:
//
// 1. An opts.borrowck_mode of `BorrowckMode::Ast` is
// 1. An opts.borrowck_mode of `BorrowckMode::Migrate` is
// synonymous with no `-Z borrowck=...` flag at all.
// (This is arguably a historical accident.)
//
// 2. `BorrowckMode::Migrate` is the limited migration to
// NLL that we are deploying with the 2018 edition.
//
// 3. We want to allow developers on the Nightly channel
// 2. We want to allow developers on the Nightly channel
// to opt back into the "hard error" mode for NLL,
// (which they can do via specifying `#![feature(nll)]`
// explicitly in their crate).
@ -1585,24 +1550,13 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
// a user's attempt to specify `-Z borrowck=compare`, which
// we arguably do not need anymore and should remove.)
//
// * Otherwise, if no `-Z borrowck=...` flag was given (or
// if `borrowck=ast` was specified), then use the default
// as required by the edition.
// * Otherwise, if no `-Z borrowck=...` then use migrate mode
//
// * Otherwise, use the behavior requested via `-Z borrowck=...`
if self.features().nll { return BorrowckMode::Mir; }
match self.sess.opts.borrowck_mode {
mode @ BorrowckMode::Mir |
mode @ BorrowckMode::Compare |
mode @ BorrowckMode::Migrate => mode,
BorrowckMode::Ast => match self.sess.edition() {
Edition::Edition2015 => BorrowckMode::Ast,
Edition::Edition2018 => BorrowckMode::Migrate,
},
}
self.sess.opts.borrowck_mode
}
#[inline]

6
src/librustc_borrowck/borrowck/mod.rs
View File

@ -49,8 +49,6 @@ pub mod gather_loans;
pub mod move_data;
mod unused;
#[derive(Clone, Copy)]
pub struct LoanDataFlowOperator;
@ -138,10 +136,6 @@ fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
check_loans::check_loans(&mut bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
}
if !tcx.use_mir_borrowck() {
unused::check(&mut bccx, body);
}
Lrc::new(BorrowCheckResult {
used_mut_nodes: bccx.used_mut_nodes.into_inner(),
signalled_any_error: bccx.signalled_any_error.into_inner(),

116
src/librustc_borrowck/borrowck/unused.rs
View File

@ -1,116 +0,0 @@
use rustc::hir::intravisit::{Visitor, NestedVisitorMap};
use rustc::hir::{self, HirId};
use rustc::lint::builtin::UNUSED_MUT;
use rustc::ty;
use rustc::util::nodemap::{FxHashMap, FxHashSet};
use errors::Applicability;
use std::slice;
use syntax::ptr::P;
use crate::borrowck::BorrowckCtxt;
pub fn check<'a, 'tcx>(bccx: &BorrowckCtxt<'a, 'tcx>, body: &'tcx hir::Body) {
let mut used_mut = bccx.used_mut_nodes.borrow().clone();
UsedMutFinder {
bccx,
set: &mut used_mut,
}.visit_expr(&body.value);
let mut cx = UnusedMutCx { bccx, used_mut };
for arg in body.arguments.iter() {
cx.check_unused_mut_pat(slice::from_ref(&arg.pat));
}
cx.visit_expr(&body.value);
}
struct UsedMutFinder<'a, 'tcx: 'a> {
bccx: &'a BorrowckCtxt<'a, 'tcx>,
set: &'a mut FxHashSet<HirId>,
}
struct UnusedMutCx<'a, 'tcx: 'a> {
bccx: &'a BorrowckCtxt<'a, 'tcx>,
used_mut: FxHashSet<HirId>,
}
impl<'a, 'tcx> UnusedMutCx<'a, 'tcx> {
fn check_unused_mut_pat(&self, pats: &[P<hir::Pat>]) {
let tcx = self.bccx.tcx;
let mut mutables: FxHashMap<_, Vec<_>> = Default::default();
for p in pats {
p.each_binding(|_, hir_id, span, ident| {
// Skip anything that looks like `_foo`
if ident.as_str().starts_with("_") {
return;
}
// Skip anything that looks like `&foo` or `&mut foo`, only look
// for by-value bindings
if let Some(&bm) = self.bccx.tables.pat_binding_modes().get(hir_id) {
match bm {
ty::BindByValue(hir::MutMutable) => {}
_ => return,
}
mutables.entry(ident.name).or_default().push((hir_id, span));
} else {
tcx.sess.delay_span_bug(span, "missing binding mode");
}
});
}
for (_name, ids) in mutables {
// If any id for this name was used mutably then consider them all
// ok, so move on to the next
if ids.iter().any(|&(ref hir_id, _)| self.used_mut.contains(hir_id)) {
continue;
}
let (hir_id, span) = ids[0];
if span.compiler_desugaring_kind().is_some() {
// If the `mut` arises as part of a desugaring, we should ignore it.
continue;
}
// Ok, every name wasn't used mutably, so issue a warning that this
// didn't need to be mutable.
let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
tcx.struct_span_lint_hir(UNUSED_MUT,
hir_id,
span,
"variable does not need to be mutable")
.span_suggestion_short(
mut_span,
"remove this `mut`",
String::new(),
Applicability::MachineApplicable,
)
.emit();
}
}
}
impl<'a, 'tcx> Visitor<'tcx> for UnusedMutCx<'a, 'tcx> {
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::OnlyBodies(&self.bccx.tcx.hir())
}
fn visit_arm(&mut self, arm: &hir::Arm) {
self.check_unused_mut_pat(&arm.pats)
}
fn visit_local(&mut self, local: &hir::Local) {
self.check_unused_mut_pat(slice::from_ref(&local.pat));
}
}
impl<'a, 'tcx> Visitor<'tcx> for UsedMutFinder<'a, 'tcx> {
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::OnlyBodies(&self.bccx.tcx.hir())
}
fn visit_nested_body(&mut self, id: hir::BodyId) {
let def_id = self.bccx.tcx.hir().body_owner_def_id(id);
self.set.extend(self.bccx.tcx.borrowck(def_id).used_mut_nodes.iter().cloned());
self.visit_body(self.bccx.tcx.hir().body(id));
}
}

5
src/librustc_mir/borrow_check/borrow_set.rs
View File

@ -303,9 +303,8 @@ impl<'a, 'gcx, 'tcx> GatherBorrows<'a, 'gcx, 'tcx> {
/// allowed to be split into separate Reservation and
/// Activation phases.
fn allow_two_phase_borrow(&self, kind: mir::BorrowKind) -> bool {
self.tcx.two_phase_borrows()
&& (kind.allows_two_phase_borrow()
|| self.tcx.sess.opts.debugging_opts.two_phase_beyond_autoref)
kind.allows_two_phase_borrow()
|| self.tcx.sess.opts.debugging_opts.two_phase_beyond_autoref
}
/// If this is a two-phase borrow, then we will record it

55
src/librustc_mir/borrow_check/mod.rs
View File

@ -74,37 +74,28 @@ fn mir_borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> BorrowC
let input_mir = tcx.mir_validated(def_id);
debug!("run query mir_borrowck: {}", tcx.def_path_str(def_id));
let mut return_early;
// Return early if we are not supposed to use MIR borrow checker for this function.
return_early = !tcx.has_attr(def_id, "rustc_mir") && !tcx.use_mir_borrowck();
// We are not borrow checking the automatically generated struct/variant constructors
// because we want to accept structs such as this (taken from the `linked-hash-map`
// crate):
// ```rust
// struct Qey<Q: ?Sized>(Q);
// ```
// MIR of this struct constructor looks something like this:
// ```rust
// fn Qey(_1: Q) -> Qey<Q>{
// let mut _0: Qey<Q>; // return place
//
// bb0: {
// (_0.0: Q) = move _1; // bb0[0]: scope 0 at src/main.rs:1:1: 1:26
// return; // bb0[1]: scope 0 at src/main.rs:1:1: 1:26
// }
// }
// ```
// The problem here is that `(_0.0: Q) = move _1;` is valid only if `Q` is
// of statically known size, which is not known to be true because of the
// `Q: ?Sized` constraint. However, it is true because the constructor can be
// called only when `Q` is of statically known size.
if tcx.is_constructor(def_id) {
// We are not borrow checking the automatically generated struct/variant constructors
// because we want to accept structs such as this (taken from the `linked-hash-map`
// crate):
// ```rust
// struct Qey<Q: ?Sized>(Q);
// ```
// MIR of this struct constructor looks something like this:
// ```rust
// fn Qey(_1: Q) -> Qey<Q>{
// let mut _0: Qey<Q>; // return place
//
// bb0: {
// (_0.0: Q) = move _1; // bb0[0]: scope 0 at src/main.rs:1:1: 1:26
// return; // bb0[1]: scope 0 at src/main.rs:1:1: 1:26
// }
// }
// ```
// The problem here is that `(_0.0: Q) = move _1;` is valid only if `Q` is
// of statically known size, which is not known to be true because of the
// `Q: ?Sized` constraint. However, it is true because the constructor can be
// called only when `Q` is of statically known size.
return_early = true;
}
if return_early {
return BorrowCheckResult {
closure_requirements: None,
used_mut_upvars: SmallVec::new(),
@ -1505,10 +1496,6 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
span: Span,
flow_state: &Flows<'cx, 'gcx, 'tcx>,
) {
if !self.infcx.tcx.two_phase_borrows() {
return;
}
// Two-phase borrow support: For each activation that is newly
// generated at this statement, check if it interferes with
// another borrow.

4
src/librustc_mir/borrow_check/nll/invalidation.rs
View File

@ -474,10 +474,6 @@ impl<'cg, 'cx, 'tcx, 'gcx> InvalidationGenerator<'cx, 'tcx, 'gcx> {
&mut self,
location: Location,
) {
if !self.tcx.two_phase_borrows() {
return;
}
// Two-phase borrow support: For each activation that is newly
// generated at this statement, check if it interferes with
// another borrow.

5
src/librustc_mir/borrow_check/nll/type_check/mod.rs
View File

@ -2672,9 +2672,8 @@ impl MirPass for TypeckMir {
let def_id = src.def_id();
debug!("run_pass: {:?}", def_id);
// When NLL is enabled, the borrow checker runs the typeck
// itself, so we don't need this MIR pass anymore.
if tcx.use_mir_borrowck() {
// FIXME: We don't need this MIR pass anymore.
if true {
return;
}

5
src/librustc_mir/borrow_check/path_utils.rs
View File

@ -15,9 +15,8 @@ pub(super) fn allow_two_phase_borrow<'a, 'tcx, 'gcx: 'tcx>(
tcx: &TyCtxt<'a, 'gcx, 'tcx>,
kind: BorrowKind
) -> bool {
tcx.two_phase_borrows()
&& (kind.allows_two_phase_borrow()
|| tcx.sess.opts.debugging_opts.two_phase_beyond_autoref)
kind.allows_two_phase_borrow()
|| tcx.sess.opts.debugging_opts.two_phase_beyond_autoref
}
/// Control for the path borrow checking code

6
src/librustc_mir/build/expr/as_place.rs
View File

@ -112,11 +112,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
}
ExprKind::SelfRef => block.and(Place::Base(PlaceBase::Local(Local::new(1)))),
ExprKind::VarRef { id } => {
let place = if this.is_bound_var_in_guard(id) && this
.hir
.tcx()
.all_pat_vars_are_implicit_refs_within_guards()
{
let place = if this.is_bound_var_in_guard(id) {
let index = this.var_local_id(id, RefWithinGuard);
Place::Base(PlaceBase::Local(index)).deref()
} else {

86
src/librustc_mir/build/matches/mod.rs
View File

@ -1425,26 +1425,22 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
// the reference that we create for the arm.
// * So we eagerly create the reference for the arm and then take a
// reference to that.
let tcx = self.hir.tcx();
let autoref = tcx.all_pat_vars_are_implicit_refs_within_guards();
if let Some(guard) = guard {
if autoref {
self.bind_matched_candidate_for_guard(
block,
&candidate.bindings,
);
let guard_frame = GuardFrame {
locals: candidate
.bindings
.iter()
.map(|b| GuardFrameLocal::new(b.var_id, b.binding_mode))
.collect(),
};
debug!("Entering guard building context: {:?}", guard_frame);
self.guard_context.push(guard_frame);
} else {
self.bind_matched_candidate_for_arm_body(block, &candidate.bindings);
}
let tcx = self.hir.tcx();
self.bind_matched_candidate_for_guard(
block,
&candidate.bindings,
);
let guard_frame = GuardFrame {
locals: candidate
.bindings
.iter()
.map(|b| GuardFrameLocal::new(b.var_id, b.binding_mode))
.collect(),
};
debug!("Entering guard building context: {:?}", guard_frame);
self.guard_context.push(guard_frame);
let re_erased = tcx.types.re_erased;
let scrutinee_source_info = self.source_info(scrutinee_span);
@ -1470,13 +1466,11 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
let source_info = self.source_info(guard.span);
let guard_end = self.source_info(tcx.sess.source_map().end_point(guard.span));
let cond = unpack!(block = self.as_local_operand(block, guard));
if autoref {
let guard_frame = self.guard_context.pop().unwrap();
debug!(
"Exiting guard building context with locals: {:?}",
guard_frame
);
}
let guard_frame = self.guard_context.pop().unwrap();
debug!(
"Exiting guard building context with locals: {:?}",
guard_frame
);
for &(_, temp) in fake_borrows {
self.cfg.push(block, Statement {
@ -1526,28 +1520,26 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
),
);
if autoref {
let by_value_bindings = candidate.bindings.iter().filter(|binding| {
if let BindingMode::ByValue = binding.binding_mode { true } else { false }
});
// Read all of the by reference bindings to ensure that the
// place they refer to can't be modified by the guard.
for binding in by_value_bindings.clone() {
let local_id = self.var_local_id(binding.var_id, RefWithinGuard);
let by_value_bindings = candidate.bindings.iter().filter(|binding| {
if let BindingMode::ByValue = binding.binding_mode { true } else { false }
});
// Read all of the by reference bindings to ensure that the
// place they refer to can't be modified by the guard.
for binding in by_value_bindings.clone() {
let local_id = self.var_local_id(binding.var_id, RefWithinGuard);
let place = Place::Base(PlaceBase::Local(local_id));
self.cfg.push(
block,
Statement {
source_info: guard_end,
kind: StatementKind::FakeRead(FakeReadCause::ForGuardBinding, place),
},
);
}
self.bind_matched_candidate_for_arm_body(
post_guard_block,
by_value_bindings,
self.cfg.push(
block,
Statement {
source_info: guard_end,
kind: StatementKind::FakeRead(FakeReadCause::ForGuardBinding, place),
},
);
}
self.bind_matched_candidate_for_arm_body(
post_guard_block,
by_value_bindings,
);
self.cfg.terminate(
post_guard_block,
@ -1604,8 +1596,6 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
}
}
// Only called when all_pat_vars_are_implicit_refs_within_guards,
// and thus all code/comments assume we are in that context.
fn bind_matched_candidate_for_guard(
&mut self,
block: BasicBlock,
@ -1739,7 +1729,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
}))),
};
let for_arm_body = self.local_decls.push(local.clone());
let locals = if has_guard.0 && tcx.all_pat_vars_are_implicit_refs_within_guards() {
let locals = if has_guard.0 {
let ref_for_guard = self.local_decls.push(LocalDecl::<'tcx> {
// This variable isn't mutated but has a name, so has to be
// immutable to avoid the unused mut lint.

130
src/librustc_mir/error_codes.rs
View File

@ -877,12 +877,14 @@ https://doc.rust-lang.org/book/ch04-00-understanding-ownership.html
"##,
E0383: r##"
#### Note: this error code is no longer emitted by the compiler.
This error occurs when an attempt is made to partially reinitialize a
structure that is currently uninitialized.
For example, this can happen when a drop has taken place:
```compile_fail,E0383
```compile_fail
struct Foo {
a: u32,
}
@ -966,10 +968,12 @@ y.set(2);
"##,*/
E0387: r##"
#### Note: this error code is no longer emitted by the compiler.
This error occurs when an attempt is made to mutate or mutably reference data
that a closure has captured immutably. Examples of this error are shown below:
```compile_fail,E0387
```compile_fail
// Accepts a function or a closure that captures its environment immutably.
// Closures passed to foo will not be able to mutate their closed-over state.
fn foo<F: Fn()>(f: F) { }
@ -1026,13 +1030,15 @@ E0388 was removed and is no longer issued.
"##,
E0389: r##"
#### Note: this error code is no longer emitted by the compiler.
An attempt was made to mutate data using a non-mutable reference. This
commonly occurs when attempting to assign to a non-mutable reference of a
mutable reference (`&(&mut T)`).
Example of erroneous code:
```compile_fail,E0389
```compile_fail
struct FancyNum {
num: u8,
}
@ -1202,6 +1208,7 @@ A variable was borrowed as mutable more than once. Erroneous code example:
let mut i = 0;
let mut x = &mut i;
let mut a = &mut i;
x;
// error: cannot borrow `i` as mutable more than once at a time
```
@ -1220,35 +1227,33 @@ let mut i = 0;
let a = &i; // ok!
let b = &i; // still ok!
let c = &i; // still ok!
b;
a;
```
"##,
E0500: r##"
A borrowed variable was used in another closure. Example of erroneous code:
A borrowed variable was used by a closure. Example of erroneous code:
```compile_fail
```compile_fail,E0500
fn you_know_nothing(jon_snow: &mut i32) {
let nights_watch = || {
*jon_snow = 2;
};
let nights_watch = &jon_snow;
let starks = || {
*jon_snow = 3; // error: closure requires unique access to `jon_snow`
// but it is already borrowed
};
println!("{}", nights_watch);
}
```
In here, `jon_snow` is already borrowed by the `nights_watch` closure, so it
In here, `jon_snow` is already borrowed by the `nights_watch` reference, so it
cannot be borrowed by the `starks` closure at the same time. To fix this issue,
you can put the closure in its own scope:
you can create the closure after the borrow has ended:
```
fn you_know_nothing(jon_snow: &mut i32) {
{
let nights_watch = || {
*jon_snow = 2;
};
} // At this point, `jon_snow` is free.
let nights_watch = &jon_snow;
println!("{}", nights_watch);
let starks = || {
*jon_snow = 3;
};
@ -1261,12 +1266,10 @@ closures:
```
fn you_know_nothing(jon_snow: &mut i32) {
let mut jon_copy = jon_snow.clone();
let nights_watch = || {
jon_copy = 2;
};
let starks = || {
*jon_snow = 3;
};
println!("{}", jon_copy);
}
```
"##,
@ -1293,26 +1296,28 @@ fn outside_closure(x: &mut i32) {
}
fn foo(a: &mut i32) {
let bar = || {
let mut bar = || {
inside_closure(a)
};
outside_closure(a); // error: cannot borrow `*a` as mutable because previous
// closure requires unique access.
bar();
}
```
To fix this error, you can place the closure in its own scope:
To fix this error, you can finish using the closure before using the captured
variable:
```
fn inside_closure(x: &mut i32) {}
fn outside_closure(x: &mut i32) {}
fn foo(a: &mut i32) {
{
let bar = || {
inside_closure(a)
};
} // borrow on `a` ends.
let mut bar = || {
inside_closure(a)
};
bar();
// borrow on `a` ends.
outside_closure(a); // ok!
}
```
@ -1324,7 +1329,7 @@ fn inside_closure(x: &mut i32) {}
fn outside_closure(x: &mut i32) {}
fn foo(a: &mut i32) {
let bar = |s: &mut i32| {
let mut bar = |s: &mut i32| {
inside_closure(s)
};
outside_closure(a);
@ -1340,9 +1345,10 @@ fn outside_closure(x: &mut i32) {}
fn foo(a: &mut i32) {
outside_closure(a);
let bar = || {
let mut bar = || {
inside_closure(a)
};
bar();
}
```
"##,
@ -1359,6 +1365,7 @@ fn foo(a: &mut i32) {
let ref y = a; // a is borrowed as immutable.
bar(a); // error: cannot borrow `*a` as mutable because `a` is also borrowed
// as immutable
println!("{}", y);
}
```
@ -1370,6 +1377,7 @@ fn bar(x: &mut i32) {}
fn foo(a: &mut i32) {
bar(a);
let ref y = a; // ok!
println!("{}", y);
}
```
@ -1385,11 +1393,11 @@ Example of erroneous code:
```compile_fail,E0503
fn main() {
let mut value = 3;
// Create a mutable borrow of `value`. This borrow
// lives until the end of this function.
let _borrow = &mut value;
// Create a mutable borrow of `value`.
let borrow = &mut value;
let _sum = value + 1; // error: cannot use `value` because
// it was mutably borrowed
println!("{}", borrow);
}
```
@ -1397,16 +1405,14 @@ In this example, `value` is mutably borrowed by `borrow` and cannot be
used to calculate `sum`. This is not possible because this would violate
Rust's mutability rules.
You can fix this error by limiting the scope of the borrow:
You can fix this error by finishing using the borrow before the next use of
the value:
```
fn main() {
let mut value = 3;
// By creating a new block, you can limit the scope
// of the reference.
{
let _borrow = &mut value; // Use `_borrow` inside this block.
}
let borrow = &mut value;
println!("{}", borrow);
// The block has ended and with it the borrow.
// You can now use `value` again.
let _sum = value + 1;
@ -1422,10 +1428,11 @@ fn main() {
let value_cloned = value.clone();
// The mutable borrow is a reference to `value` and
// not to `value_cloned`...
let _borrow = &mut value;
let borrow = &mut value;
// ... which means we can still use `value_cloned`,
let _sum = value_cloned + 1;
// even though the borrow only ends here.
println!("{}", borrow);
}
```
@ -1434,12 +1441,14 @@ http://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html
"##,
E0504: r##"
#### Note: this error code is no longer emitted by the compiler.
This error occurs when an attempt is made to move a borrowed variable into a
closure.
Example of erroneous code:
```compile_fail,E0504
```compile_fail
struct FancyNum {
num: u8,
}
@ -1577,9 +1586,10 @@ fn eat(val: &Value) {}
fn main() {
let x = Value{};
let _ref_to_val: &Value = &x;
let ref_to_val: &Value = &x;
eat(&x); // pass by reference, if it's possible
borrow(_ref_to_val);
borrow(ref_to_val);
}
```
@ -1594,11 +1604,11 @@ fn eat(val: Value) {}
fn main() {
let x = Value{};
{
let _ref_to_val: &Value = &x;
borrow(_ref_to_val);
}
eat(x); // release borrow and then move it.
let ref_to_val: &Value = &x;
borrow(ref_to_val);
// ref_to_val is no longer used.
eat(x);
}
```
@ -1614,9 +1624,9 @@ fn eat(val: Value) {}
fn main() {
let x = Value{};
let _ref_to_val: &Value = &x;
let ref_to_val: &Value = &x;
eat(x); // it will be copied here.
borrow(_ref_to_val);
borrow(ref_to_val);
}
```
@ -2053,11 +2063,13 @@ fn get_owned_iterator() -> IntoIter<i32> {
"##,
E0595: r##"
#### Note: this error code is no longer emitted by the compiler.
Closures cannot mutate immutable captured variables.
Erroneous code example:
```compile_fail,E0595
```compile_fail,E0594
let x = 3; // error: closure cannot assign to immutable local variable `x`
let mut c = || { x += 1 };
```
@ -2090,8 +2102,7 @@ let y = &mut x; // ok!
"##,
E0597: r##"
This error occurs because a borrow was made inside a variable which has a
greater lifetime than the borrowed one.
This error occurs because a value was dropped while it was still borrowed
Example of erroneous code:
@ -2101,23 +2112,28 @@ struct Foo<'a> {
}
let mut x = Foo { x: None };
let y = 0;
x.x = Some(&y); // error: `y` does not live long enough
{
let y = 0;
x.x = Some(&y); // error: `y` does not live long enough
}
println!("{:?}", x.x);
```
In here, `x` is created before `y` and therefore has a greater lifetime. Always
keep in mind that values in a scope are dropped in the opposite order they are
created. So to fix the previous example, just make the `y` lifetime greater than
the `x`'s one:
In here, `y` is dropped at the end of the inner scope, but it is borrowed by
`x` until the `println`. To fix the previous example, just remove the scope
so that `y` isn't dropped until after the println
```
struct Foo<'a> {
x: Option<&'a u32>,
}
let y = 0;
let mut x = Foo { x: None };
let y = 0;
x.x = Some(&y);
println!("{:?}", x.x);
```
"##,

6
src/librustc_mir/hair/pattern/check_match.rs
View File

@ -565,7 +565,7 @@ fn check_legality_of_move_bindings(
let mut err = struct_span_err!(cx.tcx.sess, p.span, E0008,
"cannot bind by-move into a pattern guard");
err.span_label(p.span, "moves value into pattern guard");
if cx.tcx.sess.opts.unstable_features.is_nightly_build() && cx.tcx.use_mir_borrowck() {
if cx.tcx.sess.opts.unstable_features.is_nightly_build() {
err.help("add #![feature(bind_by_move_pattern_guards)] to the \
crate attributes to enable");
}
@ -649,9 +649,7 @@ impl<'a, 'tcx> Delegate<'tcx> for MutationChecker<'a, 'tcx> {
let mut err = struct_span_err!(self.cx.tcx.sess, span, E0301,
"cannot mutably borrow in a pattern guard");
err.span_label(span, "borrowed mutably in pattern guard");
if self.cx.tcx.sess.opts.unstable_features.is_nightly_build() &&
self.cx.tcx.use_mir_borrowck()
{
if self.cx.tcx.sess.opts.unstable_features.is_nightly_build() {
err.help("add #![feature(bind_by_move_pattern_guards)] to the \
crate attributes to enable");
}

2
src/librustc_mir/util/borrowck_errors.rs
View File

@ -40,7 +40,7 @@ impl Origin {
pub fn should_emit_errors(self, mode: BorrowckMode) -> bool {
match self {
Origin::Ast => mode.use_ast(),
Origin::Mir => mode.use_mir(),
Origin::Mir => true,
}
}
}

4
src/libsyntax/feature_gate.rs
View File

@ -445,9 +445,7 @@ declare_features! (
(active, custom_inner_attributes, "1.30.0", Some(54726), None),
// Allow mixing of bind-by-move in patterns and references to
// those identifiers in guards, *if* we are using MIR-borrowck
// (aka NLL). Essentially this means you need to be using the
// 2018 edition or later.
// those identifiers in guards.
(active, bind_by_move_pattern_guards, "1.30.0", Some(15287), None),
// Allows `impl Trait` in bindings (`let`, `const`, `static`).