Use hygiene for AST passes
AST passes are now able to have resolve consider their expansions as if they were opaque macros defined either in some module in the current crate, or a fake empty module with `#[no_implicit_prelude]`.
* Add an ExpnKind for AST passes.
* Remove gensyms in AST passes.
* Remove gensyms in`#[test]`, `#[bench]` and `#[test_case]`.
* Allow opaque macros to define tests.
* Move tests for unit tests to their own directory.
* Remove `Ident::{gensym, is_gensymed}` - `Ident::gensym_if_underscore` still exists.
cc #60869, #61019
r? @petrochenkov
or-patterns: Uniformly use `PatKind::Or` in AST & Fix/Cleanup resolve
Following up on work in https://github.com/rust-lang/rust/pull/63693 and https://github.com/rust-lang/rust/pull/61708, in this PR we:
- Uniformly use `PatKind::Or(...)` in AST:
- Change `ast::Arm.pats: Vec<P<Pat>>` => `ast::Arm.pat: P<Pat>`
- Change `ast::ExprKind::Let.0: Vec<P<Pat>>` => `ast::ExprKind::Let.0: P<Pat>`
- Adjust `librustc_resolve/late.rs` to correctly handle or-patterns at any level of nesting as a result.
In particular, the already-bound check which rejects e.g. `let (a, a);` now accounts for or-patterns. The consistency checking (ensures no missing bindings and binding mode consistency) also now accounts for or-patterns. In the process, a bug was found in the current compiler which allowed:
```rust
enum E<T> { A(T, T), B(T) }
use E::*;
fn foo() {
match A(0, 1) {
B(mut a) | A(mut a, mut a) => {}
}
}
```
The new algorithms took a few iterations to get right. I tried several clever schemes but ultimately a version based on a stack of hashsets and recording product/sum contexts was chosen since it is more clearly correct.
- Clean up `librustc_resolve/late.rs` by, among other things, using a new `with_rib` function to better ensure stack dicipline.
- Do not push the change in AST to HIR for now to avoid doing too much in this PR. To cope with this, we introduce a temporary hack in `rustc::hir::lowering` (clearly marked in the diff).
cc https://github.com/rust-lang/rust/issues/54883
cc @dlrobertson @matthewjasper
r? @petrochenkov
Change opaque type syntax from `existential type` to type alias `impl Trait`
This implements a new feature gate `type_alias_impl_trait` (this is slightly different from the originally proposed feature name, but matches what has been used in discussion since), deprecating the old `existential_types` feature.
The syntax for opaque types has been changed. In addition, the "existential" terminology has been replaced with "opaque", as per previous discussion and the RFC.
This makes partial progress towards implementing https://github.com/rust-lang/rust/issues/63063.
r? @Centril
Implement RFC 2707 + Parser recovery for range patterns
Implement https://github.com/rust-lang/rfcs/pull/2707.
- Add a new basic syntactic pattern form `ast::PatKind::Rest` (parsed as `..` or `DOTDOT`) and simplify `ast::PatKind::{Slice, Tuple, TupleStruct}` as a result.
- Lower `ast::PatKind::Rest` in combination with the aforementioned `PatKind` variants as well as `PatKind::Ident`. The HIR remains unchanged for now (may be advisable to make slight adjustments later).
- Refactor `parser.rs` wrt. parsing sequences and lists of things in the process.
- Add parser recovery for range patterns of form `X..`, `X..=`, `X...`, `..Y`, `..=Y`, and `...Y`.
This should make it easy to actually support these patterns semantically later if we so desire.
cc https://github.com/rust-lang/rust/issues/62254
r? @petrochenkov
