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Rollup merge of #133493 - lcnr:fulfill-fudge, r=compiler-errors
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do not constrain infer vars in `find_best_leaf_obligation`

This ended up causing an ICE by making the following code path reachable by incorrectly constraining an inference variable while computing the best obligation for a preceding ambiguity. Closes #129444.

https://github.com/rust-lang/rust/blob/f2abf827c128120ed7a874d02973947968c158b8/compiler/rustc_trait_selection/src/solve/fulfill.rs#L312-L314

I have to be honest, I don't fully understand how that change removes all the additional diagnostics :3

r? `@compiler-errors`
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matthiaskrgr authored Nov 27, 2024
2 parents 3cce78b + fa66288 commit 762a661
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17 changes: 13 additions & 4 deletions compiler/rustc_trait_selection/src/solve/fulfill.rs
Original file line number Diff line number Diff line change
Expand Up @@ -346,12 +346,21 @@ fn find_best_leaf_obligation<'tcx>(
consider_ambiguities: bool,
) -> PredicateObligation<'tcx> {
let obligation = infcx.resolve_vars_if_possible(obligation.clone());
// FIXME: we use a probe here as the `BestObligation` visitor does not
// check whether it uses candidates which get shadowed by where-bounds.
//
// We should probably fix the visitor to not do so instead, as this also
// means the leaf obligation may be incorrect.
infcx
.visit_proof_tree(obligation.clone().into(), &mut BestObligation {
obligation: obligation.clone(),
consider_ambiguities,
.fudge_inference_if_ok(|| {
infcx
.visit_proof_tree(obligation.clone().into(), &mut BestObligation {
obligation: obligation.clone(),
consider_ambiguities,
})
.break_value()
.ok_or(())
})
.break_value()
.unwrap_or(obligation)
}

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15 changes: 0 additions & 15 deletions tests/crashes/129444.rs

This file was deleted.

20 changes: 20 additions & 0 deletions tests/ui/coherence/fuzzing/best-obligation-ICE.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
// A regression test for #129444. This previously ICE'd as
// computing the best obligation for one ambiguous obligation
// added spurious inference constraints which caused another
// candidate to pass.
trait Trait {
type Assoc;
}

struct W<T: Trait>(*mut T);
impl<T> Trait for W<W<W<T>>> {}
//~^ ERROR the trait bound `W<W<T>>: Trait` is not satisfied
//~| ERROR the trait bound `W<T>: Trait` is not satisfied
//~| ERROR the trait bound `T: Trait` is not satisfied
//~| ERROR not all trait items implemented, missing: `Assoc`

trait NoOverlap {}
impl<T: Trait> NoOverlap for T {}
impl<T: Trait<Assoc = u32>> NoOverlap for W<T> {}
//~^ ERROR conflicting implementations of trait `NoOverlap` for type `W<W<W<W<_>>>>`
fn main() {}
69 changes: 69 additions & 0 deletions tests/ui/coherence/fuzzing/best-obligation-ICE.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,69 @@
error[E0277]: the trait bound `W<W<T>>: Trait` is not satisfied
--> $DIR/best-obligation-ICE.rs:10:19
|
LL | impl<T> Trait for W<W<W<T>>> {}
| ^^^^^^^^^^ the trait `Trait` is not implemented for `W<W<T>>`
|
note: required by a bound in `W`
--> $DIR/best-obligation-ICE.rs:9:13
|
LL | struct W<T: Trait>(*mut T);
| ^^^^^ required by this bound in `W`
help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
|
LL | impl<T> Trait for W<W<W<T>>> where W<W<T>>: Trait {}
| ++++++++++++++++++++

error[E0277]: the trait bound `W<T>: Trait` is not satisfied
--> $DIR/best-obligation-ICE.rs:10:19
|
LL | impl<T> Trait for W<W<W<T>>> {}
| ^^^^^^^^^^ the trait `Trait` is not implemented for `W<T>`
|
note: required by a bound in `W`
--> $DIR/best-obligation-ICE.rs:9:13
|
LL | struct W<T: Trait>(*mut T);
| ^^^^^ required by this bound in `W`
help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
|
LL | impl<T> Trait for W<W<W<T>>> where W<T>: Trait {}
| +++++++++++++++++

error[E0277]: the trait bound `T: Trait` is not satisfied
--> $DIR/best-obligation-ICE.rs:10:19
|
LL | impl<T> Trait for W<W<W<T>>> {}
| ^^^^^^^^^^ the trait `Trait` is not implemented for `T`
|
note: required by a bound in `W`
--> $DIR/best-obligation-ICE.rs:9:13
|
LL | struct W<T: Trait>(*mut T);
| ^^^^^ required by this bound in `W`
help: consider restricting type parameter `T`
|
LL | impl<T: Trait> Trait for W<W<W<T>>> {}
| +++++++

error[E0046]: not all trait items implemented, missing: `Assoc`
--> $DIR/best-obligation-ICE.rs:10:1
|
LL | type Assoc;
| ---------- `Assoc` from trait
...
LL | impl<T> Trait for W<W<W<T>>> {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `Assoc` in implementation

error[E0119]: conflicting implementations of trait `NoOverlap` for type `W<W<W<W<_>>>>`
--> $DIR/best-obligation-ICE.rs:18:1
|
LL | impl<T: Trait> NoOverlap for T {}
| ------------------------------ first implementation here
LL | impl<T: Trait<Assoc = u32>> NoOverlap for W<T> {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `W<W<W<W<_>>>>`

error: aborting due to 5 previous errors

Some errors have detailed explanations: E0046, E0119, E0277.
For more information about an error, try `rustc --explain E0046`.
30 changes: 3 additions & 27 deletions tests/ui/impl-trait/unsized_coercion.next.stderr
Original file line number Diff line number Diff line change
@@ -1,35 +1,11 @@
error[E0277]: the size for values of type `dyn Trait` cannot be known at compilation time
--> $DIR/unsized_coercion.rs:15:17
--> $DIR/unsized_coercion.rs:14:17
|
LL | let x = hello();
| ^^^^^^^ doesn't have a size known at compile-time
|
= help: the trait `Sized` is not implemented for `dyn Trait`

error[E0308]: mismatched types
--> $DIR/unsized_coercion.rs:19:5
|
LL | fn hello() -> Box<impl Trait> {
| ---------------
| | |
| | the expected opaque type
| expected `Box<impl Trait>` because of return type
...
LL | Box::new(1u32)
| ^^^^^^^^^^^^^^ types differ
|
= note: expected struct `Box<impl Trait>`
found struct `Box<u32>`

error[E0277]: the size for values of type `dyn Trait` cannot be known at compilation time
--> $DIR/unsized_coercion.rs:12:1
|
LL | fn hello() -> Box<impl Trait> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
|
= help: the trait `Sized` is not implemented for `dyn Trait`

error: aborting due to 3 previous errors
error: aborting due to 1 previous error

Some errors have detailed explanations: E0277, E0308.
For more information about an error, try `rustc --explain E0277`.
For more information about this error, try `rustc --explain E0277`.
3 changes: 1 addition & 2 deletions tests/ui/impl-trait/unsized_coercion.rs
Original file line number Diff line number Diff line change
Expand Up @@ -10,13 +10,12 @@ trait Trait {}
impl Trait for u32 {}

fn hello() -> Box<impl Trait> {
//[next]~^ ERROR the size for values of type `dyn Trait` cannot be known at compilation time
if true {
let x = hello();
//[next]~^ ERROR: the size for values of type `dyn Trait` cannot be known at compilation time
let y: Box<dyn Trait> = x;
}
Box::new(1u32) //[next]~ ERROR: mismatched types
Box::new(1u32)
}

fn main() {}
30 changes: 3 additions & 27 deletions tests/ui/impl-trait/unsized_coercion3.next.stderr
Original file line number Diff line number Diff line change
@@ -1,35 +1,11 @@
error[E0277]: the trait bound `dyn Send: Trait` is not satisfied
--> $DIR/unsized_coercion3.rs:14:17
--> $DIR/unsized_coercion3.rs:13:17
|
LL | let x = hello();
| ^^^^^^^ the trait `Trait` is not implemented for `dyn Send`
|
= help: the trait `Trait` is implemented for `u32`

error[E0308]: mismatched types
--> $DIR/unsized_coercion3.rs:19:5
|
LL | fn hello() -> Box<impl Trait + ?Sized> {
| ------------------------
| | |
| | the expected opaque type
| expected `Box<impl Trait + ?Sized>` because of return type
...
LL | Box::new(1u32)
| ^^^^^^^^^^^^^^ types differ
|
= note: expected struct `Box<impl Trait + ?Sized>`
found struct `Box<u32>`

error[E0277]: the trait bound `dyn Send: Trait` is not satisfied
--> $DIR/unsized_coercion3.rs:11:1
|
LL | fn hello() -> Box<impl Trait + ?Sized> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait` is not implemented for `dyn Send`
|
= help: the trait `Trait` is implemented for `u32`

error: aborting due to 3 previous errors
error: aborting due to 1 previous error

Some errors have detailed explanations: E0277, E0308.
For more information about an error, try `rustc --explain E0277`.
For more information about this error, try `rustc --explain E0277`.
2 changes: 1 addition & 1 deletion tests/ui/impl-trait/unsized_coercion3.old.stderr
Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
error[E0277]: the size for values of type `impl Trait + ?Sized` cannot be known at compilation time
--> $DIR/unsized_coercion3.rs:16:32
--> $DIR/unsized_coercion3.rs:15:32
|
LL | let y: Box<dyn Send> = x;
| ^ doesn't have a size known at compile-time
Expand Down
2 changes: 0 additions & 2 deletions tests/ui/impl-trait/unsized_coercion3.rs
Original file line number Diff line number Diff line change
Expand Up @@ -9,15 +9,13 @@ trait Trait {}
impl Trait for u32 {}

fn hello() -> Box<impl Trait + ?Sized> {
//[next]~^ ERROR: the trait bound `dyn Send: Trait` is not satisfied
if true {
let x = hello();
//[next]~^ ERROR: the trait bound `dyn Send: Trait` is not satisfied
let y: Box<dyn Send> = x;
//[old]~^ ERROR: the size for values of type `impl Trait + ?Sized` cannot be know
}
Box::new(1u32)
//[next]~^ ERROR: mismatched types
}

fn main() {}
Original file line number Diff line number Diff line change
Expand Up @@ -14,13 +14,7 @@ fn main() {

fn weird0() -> impl Sized + !Sized {}
//~^ ERROR the trait bound `(): !Sized` is not satisfied
//~| ERROR the trait bound `(): !Sized` is not satisfied
//~| ERROR the trait bound `(): !Sized` is not satisfied
fn weird1() -> impl !Sized + Sized {}
//~^ ERROR the trait bound `(): !Sized` is not satisfied
//~| ERROR the trait bound `(): !Sized` is not satisfied
//~| ERROR the trait bound `(): !Sized` is not satisfied
fn weird2() -> impl !Sized {}
//~^ ERROR the trait bound `(): !Sized` is not satisfied
//~| ERROR the trait bound `(): !Sized` is not satisfied
//~| ERROR the trait bound `(): !Sized` is not satisfied
Original file line number Diff line number Diff line change
Expand Up @@ -5,53 +5,17 @@ LL | fn weird0() -> impl Sized + !Sized {}
| ^^^^^^^^^^^^^^^^^^^ the trait bound `(): !Sized` is not satisfied

error[E0277]: the trait bound `(): !Sized` is not satisfied
--> $DIR/opaque-type-unsatisfied-bound.rs:15:36
|
LL | fn weird0() -> impl Sized + !Sized {}
| ^^ the trait bound `(): !Sized` is not satisfied

error[E0277]: the trait bound `(): !Sized` is not satisfied
--> $DIR/opaque-type-unsatisfied-bound.rs:15:1
|
LL | fn weird0() -> impl Sized + !Sized {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait bound `(): !Sized` is not satisfied

error[E0277]: the trait bound `(): !Sized` is not satisfied
--> $DIR/opaque-type-unsatisfied-bound.rs:19:16
--> $DIR/opaque-type-unsatisfied-bound.rs:17:16
|
LL | fn weird1() -> impl !Sized + Sized {}
| ^^^^^^^^^^^^^^^^^^^ the trait bound `(): !Sized` is not satisfied

error[E0277]: the trait bound `(): !Sized` is not satisfied
--> $DIR/opaque-type-unsatisfied-bound.rs:19:36
|
LL | fn weird1() -> impl !Sized + Sized {}
| ^^ the trait bound `(): !Sized` is not satisfied

error[E0277]: the trait bound `(): !Sized` is not satisfied
--> $DIR/opaque-type-unsatisfied-bound.rs:19:1
|
LL | fn weird1() -> impl !Sized + Sized {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait bound `(): !Sized` is not satisfied

error[E0277]: the trait bound `(): !Sized` is not satisfied
--> $DIR/opaque-type-unsatisfied-bound.rs:23:16
--> $DIR/opaque-type-unsatisfied-bound.rs:19:16
|
LL | fn weird2() -> impl !Sized {}
| ^^^^^^^^^^^ the trait bound `(): !Sized` is not satisfied

error[E0277]: the trait bound `(): !Sized` is not satisfied
--> $DIR/opaque-type-unsatisfied-bound.rs:23:28
|
LL | fn weird2() -> impl !Sized {}
| ^^ the trait bound `(): !Sized` is not satisfied

error[E0277]: the trait bound `(): !Sized` is not satisfied
--> $DIR/opaque-type-unsatisfied-bound.rs:23:1
|
LL | fn weird2() -> impl !Sized {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait bound `(): !Sized` is not satisfied

error[E0277]: the trait bound `impl !Trait: Trait` is not satisfied
--> $DIR/opaque-type-unsatisfied-bound.rs:12:13
|
Expand All @@ -66,6 +30,6 @@ note: required by a bound in `consume`
LL | fn consume(_: impl Trait) {}
| ^^^^^ required by this bound in `consume`

error: aborting due to 10 previous errors
error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0277`.
Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,5 @@

fn produce() -> impl !Fn<(u32,)> {}
//~^ ERROR the trait bound `(): !Fn(u32)` is not satisfied
//~| ERROR the trait bound `(): !Fn(u32)` is not satisfied
//~| ERROR the trait bound `(): !Fn(u32)` is not satisfied

fn main() {}
Original file line number Diff line number Diff line change
Expand Up @@ -4,18 +4,6 @@ error[E0277]: the trait bound `(): !Fn(u32)` is not satisfied
LL | fn produce() -> impl !Fn<(u32,)> {}
| ^^^^^^^^^^^^^^^^ the trait bound `(): !Fn(u32)` is not satisfied

error[E0277]: the trait bound `(): !Fn(u32)` is not satisfied
--> $DIR/opaque-type-unsatisfied-fn-bound.rs:5:34
|
LL | fn produce() -> impl !Fn<(u32,)> {}
| ^^ the trait bound `(): !Fn(u32)` is not satisfied

error[E0277]: the trait bound `(): !Fn(u32)` is not satisfied
--> $DIR/opaque-type-unsatisfied-fn-bound.rs:5:1
|
LL | fn produce() -> impl !Fn<(u32,)> {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait bound `(): !Fn(u32)` is not satisfied

error: aborting due to 3 previous errors
error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.

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