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
Unconfigure compiler unit test files during normal build
I haven't touched libstd though, it had a lot of tests and I'm not sure the people maintaining it want this.
Closes https://github.com/rust-lang/rust/issues/61097
r? @Mark-Simulacrum
cleanup StringReader fields
reduce visibility and replace `Lrc<SourceFile>` with `start_pos`: the single bit we actually *need* from the file.
r? @petrochenkov
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
move unescape module to rustc_lexer
It makes sense to keep the definition of escape sequences closer to the lexer itself, and it is also a bit of code that I would like to share with rust-analyzer.
r? @petrochenkov
The idea here is to make a reusable library out of the existing
rust-lexer, by separating out pure lexing and rustc-specific concerns,
like spans, error reporting an interning.
So, rustc_lexer operates directly on `&str`, produces simple tokens
which are a pair of type-tag and a bit of original text, and does not
report errors, instead storing them as flags on the token.
