CTFE: avoid emitting a hard error on generic normalization failures
Fixesrust-lang/rust#149081.
The fix is quite unsatisfying and should not be necessary, cc rust-lang/rust#149283. That change is significantly more involved. This temporary fix introduces some unnecessary complexity and may hide other type system bugs.
cc ````@rust-lang/types```` I think we should try to fix issue rust-lang/rust#149283 in the near future and then remove this hack again.
I originally intended a more targeted fix. I wanted to skip evaluating constants in MIR opts if their body was polymorphic and the current generic arguments still reference generic parameters. Notes from looking into this:
- we only fetch the MIR in the `eval_to_allocation_raw` query
- figuring out which MIR to use is hard
- dealing with trivial consts is annoying
- need to resolve instances for associated consts
- implementing this by hand is hard
- inlining handles this issue by bailing on literally all normalization failures, even the ones that imply an unsoundness
- `try_normalize_after_erasing_regions` generally does two things
- deal with ambiguity after inlining
- deal with error tainting issues (please don't, we should stop doing that)
- CTFE could be changed to always silently ignore normalization failures if we're in a generic body
- hides actual bugs <- went with this option
r? types
When encountering an unmet trait bound, point at local type that doesn't implement the trait:
```
error[E0277]: the trait bound `Bar<T>: Foo` is not satisfied
--> $DIR/issue-64855.rs:9:19
|
LL | pub struct Bar<T>(<Self as Foo>::Type) where Self: ;
| ^^^^^^^^^^^^^^^^^^^ unsatisfied trait bound
|
help: the trait `Foo` is not implemented for `Bar<T>`
--> $DIR/issue-64855.rs:9:1
|
LL | pub struct Bar<T>(<Self as Foo>::Type) where Self: ;
| ^^^^^^^^^^^^^^^^^
```
Change the implicit `Sized` `Obligation` `Span` for call expressions to
include the whole expression. This aids the existing deduplication
machinery to reduce the number of errors caused by a single unsized
expression.
