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Only check for errors in predicate when skipping impl assembly

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Prior to PR #91205, checking for errors in the overall obligation
would check checking the `ParamEnv`, due to an incorrect
`super_visit_with` impl. With this bug fixed, we will now
bail out of impl candidate assembly if the `ParamEnv` contains
any error types.

In practice, this appears to be overly conservative - when an error
occurs early in compilation, we end up giving up early for some
predicates that we could have successfully evaluated without overflow.
By only checking for errors in the predicate itself, we avoid causing
additional spurious 'type annotations needed' errors after a 'real'
error has already occurred.

With this PR, the diagnostic changes caused by PR #91205 are reverted.
This commit is contained in:
Aaron Hill
2021-11-26 09:14:16 -06:00
committed by Pietro Albini
parent b16715751a
commit 70a61c97cb
6 changed files with 28 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files
compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+4 -1
View File
@@ -536,7 +536,10 @@ fn assemble_candidates_from_impls(
// 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() {
// We don't check for errors in the `ParamEnv` - in practice,
// it seems to cause us to be overly aggressive in deciding
// to give up searching for candidates, leading to spurious errors.
if obligation.predicate.references_error() {
return;
}
src/test/ui/const-generics/generic_const_exprs/issue-72787.min.stderr
+7 -15
View File
@@ -1,5 +1,5 @@
error: generic parameters may not be used in const operations
--> $DIR/issue-72787.rs:12:17
--> $DIR/issue-72787.rs:11:17
|
LL | Condition<{ LHS <= RHS }>: True
| ^^^ cannot perform const operation using `LHS`
@@ -8,7 +8,7 @@ LL | Condition<{ LHS <= RHS }>: True
= help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
--> $DIR/issue-72787.rs:12:24
--> $DIR/issue-72787.rs:11:24
|
LL | Condition<{ LHS <= RHS }>: True
| ^^^ cannot perform const operation using `RHS`
@@ -17,7 +17,7 @@ LL | Condition<{ LHS <= RHS }>: True
= help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
--> $DIR/issue-72787.rs:26:25
--> $DIR/issue-72787.rs:25:25
|
LL | IsLessOrEqual<{ 8 - I }, { 8 - J }>: True,
| ^ cannot perform const operation using `I`
@@ -26,7 +26,7 @@ LL | IsLessOrEqual<{ 8 - I }, { 8 - J }>: True,
= help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
--> $DIR/issue-72787.rs:26:36
--> $DIR/issue-72787.rs:25:36
|
LL | IsLessOrEqual<{ 8 - I }, { 8 - J }>: True,
| ^ cannot perform const operation using `J`
@@ -35,15 +35,7 @@ LL | IsLessOrEqual<{ 8 - I }, { 8 - J }>: True,
= help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
error[E0283]: type annotations needed
--> $DIR/issue-72787.rs:10:38
|
LL | impl<const LHS: u32, const RHS: u32> True for IsLessOrEqual<LHS, RHS> where
| ^^^^ cannot infer type for struct `IsLessOrEqual<LHS, RHS>`
|
= note: cannot satisfy `IsLessOrEqual<LHS, RHS>: True`
error[E0283]: type annotations needed
--> $DIR/issue-72787.rs:22:26
--> $DIR/issue-72787.rs:21:26
|
LL | IsLessOrEqual<I, 8>: True,
| ^^^^ cannot infer type for struct `IsLessOrEqual<I, 8_u32>`
@@ -51,13 +43,13 @@ LL | IsLessOrEqual<I, 8>: True,
= note: cannot satisfy `IsLessOrEqual<I, 8_u32>: True`
error[E0283]: type annotations needed
--> $DIR/issue-72787.rs:22:26
--> $DIR/issue-72787.rs:21:26
|
LL | IsLessOrEqual<I, 8>: True,
| ^^^^ cannot infer type for struct `IsLessOrEqual<I, 8_u32>`
|
= note: cannot satisfy `IsLessOrEqual<I, 8_u32>: True`
error: aborting due to 7 previous errors
error: aborting due to 6 previous errors
For more information about this error, try `rustc --explain E0283`.
src/test/ui/const-generics/generic_const_exprs/issue-72787.rs
-1
View File
@@ -8,7 +8,6 @@
pub trait True {}
impl<const LHS: u32, const RHS: u32> True for IsLessOrEqual<LHS, RHS> where
//[min]~^ ERROR type annotations needed
Condition<{ LHS <= RHS }>: True
//[min]~^ Error generic parameters may not be used in const operations
//[min]~| Error generic parameters may not be used in const operations
src/test/ui/issues/issue-77919.rs
+1 -1
View File
@@ -10,4 +10,4 @@ struct Multiply<N, M> {
}
impl<N, M> TypeVal<usize> for Multiply<N, M> where N: TypeVal<VAL> {}
//~^ ERROR cannot find type `VAL` in this scope
//~| ERROR type annotations needed
//~| ERROR not all trait items implemented, missing: `VAL`
src/test/ui/issues/issue-77919.stderr
+8 -7
View File
@@ -17,15 +17,16 @@ LL | impl<N, M> TypeVal<usize> for Multiply<N, M> where N: TypeVal<VAL> {}
| |
| help: you might be missing a type parameter: `, VAL`
error[E0283]: type annotations needed
--> $DIR/issue-77919.rs:11:12
error[E0046]: not all trait items implemented, missing: `VAL`
--> $DIR/issue-77919.rs:11:1
|
LL | const VAL: T;
| ------------- `VAL` from trait
...
LL | impl<N, M> TypeVal<usize> for Multiply<N, M> where N: TypeVal<VAL> {}
| ^^^^^^^^^^^^^^ cannot infer type for struct `Multiply<N, M>`
|
= note: cannot satisfy `Multiply<N, M>: TypeVal<usize>`
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `VAL` in implementation
error: aborting due to 3 previous errors
Some errors have detailed explanations: E0283, E0412.
For more information about an error, try `rustc --explain E0283`.
Some errors have detailed explanations: E0046, E0412.
For more information about an error, try `rustc --explain E0046`.
src/tools/clippy/tests/ui/crashes/ice-6252.stderr
+8 -7
View File
@@ -21,15 +21,16 @@ LL | impl<N, M> TypeVal<usize> for Multiply<N, M> where N: TypeVal<VAL> {}
| |
| help: you might be missing a type parameter: `, VAL`
error[E0283]: type annotations needed
--> $DIR/ice-6252.rs:10:12
error[E0046]: not all trait items implemented, missing: `VAL`
--> $DIR/ice-6252.rs:10:1
|
LL | const VAL: T;
| ------------- `VAL` from trait
...
LL | impl<N, M> TypeVal<usize> for Multiply<N, M> where N: TypeVal<VAL> {}
| ^^^^^^^^^^^^^^ cannot infer type for struct `Multiply<N, M>`
|
= note: cannot satisfy `Multiply<N, M>: TypeVal<usize>`
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `VAL` in implementation
error: aborting due to 3 previous errors
Some errors have detailed explanations: E0283, E0412.
For more information about an error, try `rustc --explain E0283`.
Some errors have detailed explanations: E0046, E0412.
For more information about an error, try `rustc --explain E0046`.