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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
parent 6b997b6576
commit 3c8b644d0d
1 changed files with 8 additions and 7 deletions
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15
tests/ui/crashes/ice-6252.stderr
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@ -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`.