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Auto merge of #113312 - Ddystopia:auto-trait-fun, r=lcnr

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discard default auto trait impls if explicit ones exist (rebase of #85048)

Rebase of #85048
This commit is contained in:
bors 2023-07-28 10:41:00 +00:00
commit e4c98caffe
8 changed files with 146 additions and 20 deletions
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6
compiler/rustc_lint_defs/src/builtin.rs
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@ -4052,12 +4052,12 @@ declare_lint! {
///
/// The compiler disables the automatic implementation if an explicit one
/// exists for given type constructor. The exact rules governing this
/// are currently unsound, quite subtle, and will be modified in the future.
/// This change will cause the automatic implementation to be disabled in more
/// were previously unsound, quite subtle, and have been recently modified.
/// This change caused the automatic implementation to be disabled in more
/// cases, potentially breaking some code.
pub SUSPICIOUS_AUTO_TRAIT_IMPLS,
Warn,
"the rules governing auto traits will change in the future",
"the rules governing auto traits have recently changed resulting in potential breakage",
@future_incompatible = FutureIncompatibleInfo {
reason: FutureIncompatibilityReason::FutureReleaseSemanticsChange,
reference: "issue #93367 <https://github.com/rust-lang/rust/issues/93367>",

66
compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
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@ -124,11 +124,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
self.assemble_candidates_from_projected_tys(obligation, &mut candidates);
self.assemble_candidates_from_caller_bounds(stack, &mut candidates)?;
// Auto implementations have lower priority, so we only
// consider triggering a default if there is no other impl that can apply.
if candidates.vec.is_empty() {
self.assemble_candidates_from_auto_impls(obligation, &mut candidates);
}
self.assemble_candidates_from_auto_impls(obligation, &mut candidates);
}
debug!("candidate list size: {}", candidates.vec.len());
Ok(candidates)
@ -513,7 +509,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
// for an example of a test case that exercises
// this path.
}
ty::Infer(ty::TyVar(_)) => {
ty::Infer(ty::TyVar(_) | ty::IntVar(_) | ty::FloatVar(_)) => {
// The auto impl might apply; we don't know.
candidates.ambiguous = true;
}
@ -533,7 +529,63 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
}
}
_ => candidates.vec.push(AutoImplCandidate),
ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
bug!(
"asked to assemble auto trait candidates of unexpected type: {:?}",
self_ty
);
}
ty::Alias(_, _)
if candidates.vec.iter().any(|c| matches!(c, ProjectionCandidate(..))) =>
{
// We do not generate an auto impl candidate for `impl Trait`s which already
// reference our auto trait.
//
// For example during candidate assembly for `impl Send: Send`, we don't have
// to look at the constituent types for this opaque types to figure out that this
// trivially holds.
//
// Note that this is only sound as projection candidates of opaque types
// are always applicable for auto traits.
}
ty::Alias(_, _) => candidates.vec.push(AutoImplCandidate),
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Str
| ty::Array(_, _)
| ty::Slice(_)
| ty::Adt(..)
| ty::RawPtr(_)
| ty::Ref(..)
| ty::FnDef(..)
| ty::FnPtr(_)
| ty::Closure(_, _)
| ty::Generator(..)
| ty::Never
| ty::Tuple(_)
| ty::GeneratorWitness(_)
| ty::GeneratorWitnessMIR(..) => {
// Only consider auto impls if there are no manual impls for the root of `self_ty`.
//
// For example, we only consider auto candidates for `&i32: Auto` if no explicit impl
// for `&SomeType: Auto` exists. Due to E0321 the only crate where impls
// for `&SomeType: Auto` can be defined is the crate where `Auto` has been defined.
//
// Generally, we have to guarantee that for all `SimplifiedType`s the only crate
// which may define impls for that type is either the crate defining the type
// or the trait. This should be guaranteed by the orphan check.
let mut has_impl = false;
self.tcx().for_each_relevant_impl(def_id, self_ty, |_| has_impl = true);
if !has_impl {
candidates.vec.push(AutoImplCandidate)
}
}
ty::Error(_) => {} // do not add an auto trait impl for `ty::Error` for now.
}
}
}

25
compiler/rustc_trait_selection/src/traits/select/mod.rs
View File

@ -1783,6 +1783,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
/// candidates and prefer where-clause candidates.
///
/// See the comment for "SelectionCandidate" for more details.
#[instrument(level = "debug", skip(self))]
fn candidate_should_be_dropped_in_favor_of(
&mut self,
victim: &EvaluatedCandidate<'tcx>,
@ -1806,13 +1807,6 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
// This is a fix for #53123 and prevents winnowing from accidentally extending the
// lifetime of a variable.
match (&other.candidate, &victim.candidate) {
(_, AutoImplCandidate) | (AutoImplCandidate, _) => {
bug!(
"default implementations shouldn't be recorded \
when there are other valid candidates"
);
}
// FIXME(@jswrenn): this should probably be more sophisticated
(TransmutabilityCandidate, _) | (_, TransmutabilityCandidate) => DropVictim::No,
@ -1854,6 +1848,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
(
ParamCandidate(ref other_cand),
ImplCandidate(..)
| AutoImplCandidate
| ClosureCandidate { .. }
| GeneratorCandidate
| FutureCandidate
@ -1881,6 +1876,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
}
(
ImplCandidate(_)
| AutoImplCandidate
| ClosureCandidate { .. }
| GeneratorCandidate
| FutureCandidate
@ -1914,6 +1910,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
(
ObjectCandidate(_) | ProjectionCandidate(..),
ImplCandidate(..)
| AutoImplCandidate
| ClosureCandidate { .. }
| GeneratorCandidate
| FutureCandidate
@ -1927,6 +1924,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
(
ImplCandidate(..)
| AutoImplCandidate
| ClosureCandidate { .. }
| GeneratorCandidate
| FutureCandidate
@ -2017,6 +2015,19 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
}
}
(AutoImplCandidate, ImplCandidate(_)) | (ImplCandidate(_), AutoImplCandidate) => {
DropVictim::No
}
(AutoImplCandidate, _) | (_, AutoImplCandidate) => {
bug!(
"default implementations shouldn't be recorded \
when there are other global candidates: {:?} {:?}",
other,
victim
);
}
// Everything else is ambiguous
(
ImplCandidate(_)

31
tests/ui/auto-traits/issue-83857-ub.rs Normal file
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@ -0,0 +1,31 @@
#![allow(suspicious_auto_trait_impls)]
struct Always<T, U>(T, U);
unsafe impl<T, U> Send for Always<T, U> {}
struct Foo<T, U>(Always<T, U>);
trait False {}
unsafe impl<U: False> Send for Foo<u32, U> {}
trait WithAssoc {
type Output;
}
impl<T: Send> WithAssoc for T {
type Output = Self;
}
impl WithAssoc for Foo<u32, ()> {
type Output = Box<i32>;
}
fn generic<T, U>(v: Foo<T, U>, f: fn(<Foo<T, U> as WithAssoc>::Output) -> i32) {
//~^ ERROR `Foo<T, U>` cannot be sent between threads safely
f(foo(v));
}
fn foo<T: Send>(x: T) -> <T as WithAssoc>::Output {
x
}
fn main() {
generic(Foo(Always(0, ())), |b| *b);
}

22
tests/ui/auto-traits/issue-83857-ub.stderr Normal file
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@ -0,0 +1,22 @@
error[E0277]: `Foo<T, U>` cannot be sent between threads safely
--> $DIR/issue-83857-ub.rs:20:38
|
LL | fn generic<T, U>(v: Foo<T, U>, f: fn(<Foo<T, U> as WithAssoc>::Output) -> i32) {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Foo<T, U>` cannot be sent between threads safely
|
= help: the trait `Send` is not implemented for `Foo<T, U>`
note: required for `Foo<T, U>` to implement `WithAssoc`
--> $DIR/issue-83857-ub.rs:13:15
|
LL | impl<T: Send> WithAssoc for T {
| ---- ^^^^^^^^^ ^
| |
| unsatisfied trait bound introduced here
help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
|
LL | fn generic<T, U>(v: Foo<T, U>, f: fn(<Foo<T, U> as WithAssoc>::Output) -> i32) where Foo<T, U>: Send {
| +++++++++++++++++++++
error: aborting due to previous error
For more information about this error, try `rustc --explain E0277`.

6
tests/ui/generator/auto-trait-regions.rs
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@ -26,7 +26,7 @@ fn assert_foo<T: Foo>(f: T) {}
fn main() {
// Make sure 'static is erased for generator interiors so we can't match it in trait selection
let x: &'static _ = &OnlyFooIfStaticRef(No);
let gen = || {
let gen = move || {
let x = x;
yield;
assert_foo(x);
@ -36,7 +36,7 @@ fn main() {
// Allow impls which matches any lifetime
let x = &OnlyFooIfRef(No);
let gen = || {
let gen = move || {
let x = x;
yield;
assert_foo(x);
@ -44,7 +44,7 @@ fn main() {
assert_foo(gen); // ok
// Disallow impls which relates lifetimes in the generator interior
let gen = || {
let gen = move || {
let a = A(&mut true, &mut true, No);
//~^ temporary value dropped while borrowed
//~| temporary value dropped while borrowed

0
tests/ui/impl-trait/auto-trait-leak Normal file
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10
tests/ui/impl-trait/recursive-auto-trait.rs Normal file
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@ -0,0 +1,10 @@
// check-pass
fn is_send<T: Send>(_: T) {}
fn foo() -> impl Send {
if false {
is_send(foo());
}
()
}
fn main() {}