Dejargonize `subst`
In favor of #110793, replace almost every occurence of `subst` and `substitution` from rustc codes, but they still remains in subtrees under `src/tools/` like clippy and test codes (I'd like to replace them after this)
- improve diagnostics of field uniqueness check and representation check
- simplify the implementation of field uniqueness check
- remove some useless codes and improvement neatness
When an associated type with GATs isn't specified in a `dyn Trait`, emit
an object safety error instead of only complaining about the missing
associated type, as it will lead the user down a path of three different
errors before letting them know that what they were trying to do is
impossible to begin with.
Fix#103155.
Correctly deny late-bound lifetimes from parent in anon consts and TAITs
Reuse the `AnonConstBoundary` scope (introduced in #108553, renamed in this PR to `LateBoundary`) to deny late-bound vars of *all* kinds (ty/const/lifetime) in anon consts and TAITs.
Side-note, but I would like to consolidate this with the error reporting for RPITs (E0657):
c4f25777a0/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs (L733-L754) but the semantics about what we're allowed to capture there are slightly different, so I'm leaving that untouched.
Fixes#115474
repr(transparent): it's fine if the one non-1-ZST field is a ZST
This code currently gets rejected:
```rust
#[repr(transparent)]
struct MyType([u16; 0])
```
That clearly seems like a bug to me: `repr(transparent)` [got defined ](https://github.com/rust-lang/rust/issues/77841#issuecomment-716575747) as having any number of 1-ZST fields plus optionally one more field; `MyType` clearly satisfies that definition.
This PR changes the `repr(transparent)` logic to actually match that definition.
Account for late-bound vars from parent arg-position impl trait
We should be reporting an error like we do for late-bound args coming from a parent APIT.
Fixes#113016
Validate fluent variable references in tests
Closes#101109
Under `cfg(test)`, the `fluent_messages` macro will emit a list of variables referenced by each message and its attributes. The derive attribute will now emit a `#[test]` that checks that each referenced variable exists in the structure it's applied to.
Min specialization improvements
- Don't allow specialization impls with no items, such implementations are probably not correct and only occur as mistakes in the compiler and standard library
- Fix a missing normalization call
- Adds spans for lifetime errors from overly general specializations
Closes#79457Closes#109815
Support return-type bounds on associated methods from supertraits
Support `T: Trait<method(): Bound>` when `method` comes from a supertrait, aligning it with the behavior of associated type bounds (both equality and trait bounds).
The only wrinkle is that I have to extend `super_predicates_that_define_assoc_type` to look for *all* items, not just `AssocKind::Ty`. This will also be needed to support `feature(associated_const_equality)` as well, which is subtly broken when it comes to supertraits, though this PR does not fix those yet. There's a slight chance there's a perf regression here, in which case I guess I could split it out into a separate query.
Such implementations are usually mistakes and are not used in the
compiler or standard library (after this commit) so forbid them with
`min_specialization`.
Explicitly reject negative and reservation drop impls
Fixes#110858
It doesn't really make sense for a type to have a `!Drop` impl. Or at least, I don't want us to implicitly assign a meaning to it by the way the compiler *currently* handles it (incompletely), and rather I would like to see a PR (or an RFC...) assign a meaning to `!Drop` if we actually wanted one for it.
Add `ConstParamTy` trait
This is a bit sketch, but idk.
r? `@BoxyUwU`
Yet to be done:
- [x] ~~Figure out if it's okay to implement `StructuralEq` for primitives / possibly remove their special casing~~ (it should be okay, but maybe not in this PR...)
- [ ] Maybe refactor the code a little bit
- [x] Use a macro to make impls a bit nicer
Future work:
- [ ] Actually™ use the trait when checking if a `const` generic type is allowed
- [ ] _Really_ refactor the surrounding code
- [ ] Refactor `marker.rs` into multiple modules for each "theme" of markers
