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Beta backport of PR rust-lang#73005 (obligation error impl candidate)
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@Aaron1011
Aaron1011 committed Jun 26, 2020
1 parent 1dc0f6d commit e461d2e
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Showing 5 changed files with 55 additions and 181 deletions.
18 changes: 18 additions & 0 deletions src/librustc_trait_selection/traits/select.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1173,6 +1173,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
// who might care about this case, like coherence, should use
// that function).
if candidates.is_empty() {
// If there's an error type, 'downgrade' our result from
// `Err(Unimplemented)` to `Ok(None)`. This helps us avoid
// emitting additional spurious errors, since we're guaranteed
// to have emitted at least one.
if stack.obligation.references_error() {
debug!("no results for error type, treating as ambiguous");
return Ok(None);
}
return Err(Unimplemented);
}

Expand Down Expand Up @@ -1697,6 +1705,16 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
) -> Result<(), SelectionError<'tcx>> {
debug!("assemble_candidates_from_impls(obligation={:?})", obligation);

// Essentially any user-written impl will match with an error type,
// so creating `ImplCandidates` isn't useful. However, we might
// end up finding a candidate elsewhere (e.g. a `BuiltinCandidate` for `Sized)
// This helps us avoid overflow: see issue #72839
// Since compilation is already guaranteed to fail, this is just
// to try to show the 'nicest' possible errors to the user.
if obligation.references_error() {
return Ok(());
}

self.tcx().for_each_relevant_impl(
obligation.predicate.def_id(),
obligation.predicate.skip_binder().trait_ref.self_ty(),
Expand Down
2 changes: 0 additions & 2 deletions src/test/ui/impl-trait/auto-trait-leak.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,8 +11,6 @@ fn main() {
// return type, which can't depend on the obligation.
fn cycle1() -> impl Clone {
//~^ ERROR cycle detected
//~| ERROR cycle detected
//~| ERROR cycle detected
send(cycle2().clone());
//~^ ERROR cannot be sent between threads safely

Expand Down
188 changes: 9 additions & 179 deletions src/test/ui/impl-trait/auto-trait-leak.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -36,37 +36,37 @@ LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
= note: ...which requires evaluating trait selection obligation `impl std::clone::Clone: std::marker::Send`...
note: ...which requires computing type of `cycle2::{{opaque}}#0`...
--> $DIR/auto-trait-leak.rs:22:16
--> $DIR/auto-trait-leak.rs:20:16
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^
note: ...which requires borrow-checking `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
--> $DIR/auto-trait-leak.rs:20:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
--> $DIR/auto-trait-leak.rs:20:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing MIR for `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
--> $DIR/auto-trait-leak.rs:20:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires unsafety-checking `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
--> $DIR/auto-trait-leak.rs:20:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires building MIR for `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
--> $DIR/auto-trait-leak.rs:20:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires type-checking `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
--> $DIR/auto-trait-leak.rs:20:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
Expand All @@ -84,178 +84,8 @@ LL | | Rc::new(String::from("foo"))
LL | | }
| |_^

error[E0391]: cycle detected when computing type of `cycle1::{{opaque}}#0`
--> $DIR/auto-trait-leak.rs:12:16
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^
|
note: ...which requires borrow-checking `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing MIR for `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires unsafety-checking `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires building MIR for `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires type-checking `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
= note: ...which requires evaluating trait selection obligation `impl std::clone::Clone: std::marker::Send`...
note: ...which requires computing type of `cycle2::{{opaque}}#0`...
--> $DIR/auto-trait-leak.rs:22:16
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^
note: ...which requires borrow-checking `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing MIR for `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires unsafety-checking `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires building MIR for `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires type-checking `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
= note: ...which again requires computing type of `cycle1::{{opaque}}#0`, completing the cycle
note: cycle used when checking item types in top-level module
--> $DIR/auto-trait-leak.rs:1:1
|
LL | / use std::cell::Cell;
LL | | use std::rc::Rc;
LL | |
LL | | fn send<T: Send>(_: T) {}
... |
LL | | Rc::new(String::from("foo"))
LL | | }
| |_^

error[E0391]: cycle detected when computing type of `cycle1::{{opaque}}#0`
--> $DIR/auto-trait-leak.rs:12:16
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^
|
note: ...which requires borrow-checking `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing MIR for `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires unsafety-checking `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires building MIR for `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires type-checking `cycle1`...
--> $DIR/auto-trait-leak.rs:12:1
|
LL | fn cycle1() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
= note: ...which requires evaluating trait selection obligation `impl std::clone::Clone: std::marker::Send`...
note: ...which requires computing type of `cycle2::{{opaque}}#0`...
--> $DIR/auto-trait-leak.rs:22:16
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^
note: ...which requires borrow-checking `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires processing MIR for `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires unsafety-checking `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires building MIR for `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...which requires type-checking `cycle2`...
--> $DIR/auto-trait-leak.rs:22:1
|
LL | fn cycle2() -> impl Clone {
| ^^^^^^^^^^^^^^^^^^^^^^^^^
= note: ...which again requires computing type of `cycle1::{{opaque}}#0`, completing the cycle
note: cycle used when checking item types in top-level module
--> $DIR/auto-trait-leak.rs:1:1
|
LL | / use std::cell::Cell;
LL | | use std::rc::Rc;
LL | |
LL | | fn send<T: Send>(_: T) {}
... |
LL | | Rc::new(String::from("foo"))
LL | | }
| |_^

error[E0277]: `std::rc::Rc<std::string::String>` cannot be sent between threads safely
--> $DIR/auto-trait-leak.rs:16:5
--> $DIR/auto-trait-leak.rs:14:5
|
LL | fn send<T: Send>(_: T) {}
| ---- required by this bound in `send`
Expand All @@ -269,7 +99,7 @@ LL | fn cycle2() -> impl Clone {
= help: within `impl std::clone::Clone`, the trait `std::marker::Send` is not implemented for `std::rc::Rc<std::string::String>`
= note: required because it appears within the type `impl std::clone::Clone`

error: aborting due to 4 previous errors
error: aborting due to 2 previous errors

Some errors have detailed explanations: E0277, E0391.
For more information about an error, try `rustc --explain E0277`.
19 changes: 19 additions & 0 deletions src/test/ui/issues/issue-72839-error-overflow.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
// Regression test for issue #72839
// Tests that we do not overflow during trait selection after
// a type error occurs
use std::ops::Rem;
trait Foo {}
struct MyStruct<T>(T);

impl<T, U> Rem<MyStruct<T>> for MyStruct<U> where MyStruct<U>: Rem<MyStruct<T>> {
type Output = u8;
fn rem(self, _: MyStruct<T>) -> Self::Output {
panic!()
}
}

fn main() {}

fn foo() {
if missing_var % 8 == 0 {} //~ ERROR cannot find
}
9 changes: 9 additions & 0 deletions src/test/ui/issues/issue-72839-error-overflow.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,9 @@
error[E0425]: cannot find value `missing_var` in this scope
--> $DIR/issue-72839-error-overflow.rs:18:8
|
LL | if missing_var % 8 == 0 {}
| ^^^^^^^^^^^ not found in this scope

error: aborting due to previous error

For more information about this error, try `rustc --explain E0425`.

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