Remove concept of 'completion' from the projection cache
Fixes#88910
When we initially store a `NormalizedTy` in the projection cache,
we discard all obligations that we can (while ensuring that we
don't cause any issues with incremental compilation).
Marking a projection cache entry as 'completed' discards all
obligations associated with it. This can only cause problems,
since any obligations stored in the cache are there for a reason
(e.g. they evaluate to `EvaluatedToOkModuloRegions`).
This commit removes `complete` and `complete_normalized` entirely.
Improve error message for type mismatch in generator arguments
Fixes#88653. The code example given there is invalid because the `Generator` trait (unlike the `Fn` traits) does not take the generator arguments in tupled-up form (because there can only be one argument, from my understanding). Hence, the type error in the example in #88653 is correct, because the given generator takes a `bool` argument, whereas the function's return type talks about a generator with a `(bool,)` argument.
The error message is both confusing and wrong, though: It is wrong because it displays the wrong "expected signature", and it is confusing because both the "expected" and "found" notes point at the same span. With my changes, I get the following, more helpful output:
```
error[E0631]: type mismatch in generator arguments
--> test.rs:5:22
|
5 | fn foo(bar: bool) -> impl Generator<(bool,)> {
| ^^^^^^^^^^^^^^^^^^^^^^^ expected signature of `fn((bool,)) -> _`
6 | |bar| {
| ----- found signature of `fn(bool) -> _`
```
Point at argument instead of call for their obligations
When an obligation is introduced by a specific `fn` argument, point at
the argument instead of the `fn` call if the obligation fails to be
fulfilled.
Move the information about pointing at the call argument expression in
an unmet obligation span from the `FulfillmentError` to a new
`ObligationCauseCode`.
When giving an error about an obligation introduced by a function call
that an argument doesn't fulfill, and that argument is a block, add a
span_label pointing at the innermost tail expression.
Current output:
```
error[E0425]: cannot find value `x` in this scope
--> f10.rs:4:14
|
4 | Some(x * 2)
| ^ not found in this scope
error[E0277]: expected a `FnOnce<({integer},)>` closure, found `Option<_>`
--> f10.rs:2:31
|
2 | let p = Some(45).and_then({
| ______________________--------_^
| | |
| | required by a bound introduced by this call
3 | | |x| println!("doubling {}", x);
4 | | Some(x * 2)
| | -----------
5 | | });
| |_____^ expected an `FnOnce<({integer},)>` closure, found `Option<_>`
|
= help: the trait `FnOnce<({integer},)>` is not implemented for `Option<_>`
```
Previous output:
```
error[E0425]: cannot find value `x` in this scope
--> f10.rs:4:14
|
4 | Some(x * 2)
| ^ not found in this scope
error[E0277]: expected a `FnOnce<({integer},)>` closure, found `Option<_>`
--> f10.rs:2:22
|
2 | let p = Some(45).and_then({
| ^^^^^^^^ expected an `FnOnce<({integer},)>` closure, found `Option<_>`
|
= help: the trait `FnOnce<({integer},)>` is not implemented for `Option<_>`
```
Partially address #27300. Will require rebasing on top of #88546.
cleanup(rustc_trait_selection): remove vestigial code from rustc_on_unimplemented
This isn't allowed by the validator, and seems to be unused.
When it was added in ed10a3faae,
it was used on `Sized`, and that usage is gone.
When giving an error about an obligation introduced by a function call
that an argument doesn't fulfill, and that argument is a block, add a
span_label pointing at the innermost tail expression.
Move the information about pointing at the call argument expression in
an unmet obligation span from the `FulfillmentError` to a new
`ObligationCauseCode`.
Const drop
The changes are pretty primitive at this point. But at least it works. ^-^
Problems with the current change that I can think of now:
- [x] `~const Drop` shouldn't change anything in the non-const world.
- [x] types that do not have drop glues shouldn't fail to satisfy `~const Drop` in const contexts. `struct S { a: u8, b: u16 }` This might not fail for `needs_non_const_drop`, but it will fail in `rustc_trait_selection`.
- [x] The current change accepts types that have `const Drop` impls but have non-const `Drop` glue.
Fixes#88424.
Significant Changes:
- `~const Drop` is no longer treated as a normal trait bound. In non-const contexts, this bound has no effect, but in const contexts, this restricts the input type and all of its transitive fields to either a) have a `const Drop` impl or b) can be trivially dropped (i.e. no drop glue)
- `T: ~const Drop` will not be linted like `T: Drop`.
- Instead of recursing and iterating through the type in `rustc_mir::transform::check_consts`, we use the trait system to special case `~const Drop`. See [`rustc_trait_selection::...::candidate_assembly#assemble_const_drop_candidates`](https://github.com/fee1-dead/rust/blob/const-drop/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs#L817) and others.
Changes not related to `const Drop`ping and/or changes that are insignificant:
- `Node.constness_for_typeck` no longer returns `hir::Constness::Const` for type aliases in traits. This was previously used to hack how we determine default bound constness for items. But because we now use an explicit opt-in, it is no longer needed.
- Removed `is_const_impl_raw` query. We have `impl_constness`, and the only existing use of that query uses `HirId`, which means we can just operate it with hir.
- `ty::Destructor` now has a field `constness`, which represents the constness of the destructor.
r? `@oli-obk`
Fixes#88910
When we initially store a `NormalizedTy` in the projection cache,
we discard all obligations that we can (while ensuring that we
don't cause any issues with incremental compilation).
Marking a projection cache entry as 'completed' discards all
obligations associated with it. This can only cause problems,
since any obligations stored in the cache are there for a reason
(e.g. they evaluate to `EvaluatedToOkModuloRegions`).
This commit removes `complete` and `complete_normalized` entirely.
Fix duplicate bounds for const_trait_impl
Fixes#88383.
Compare the constness of the candidates before winnowing and removing a `~const` `BoundCandidate`.
generic_const_exprs: use thir for abstract consts instead of mir
Changes `AbstractConst` building to use `thir` instead of `mir` so that there's less chance of consts unifying when they shouldn't because lowering to mir dropped information (see `abstract-consts-as-cast-5.rs` test)
r? `@lcnr`
