Move arg/constraint partition check to validation & improve recovery
- In the first commit, we move the check rejecting e.g., `<'a, Item = u8, String>` from the parser into AST validation.
- We then use this to improve the code for parsing generic arguments.
- And we add recovery for e.g., `<Item = >` (missing), `<Item = 42>` (constant), and `<Item = 'a>` (lifetime).
This is also preparatory work for supporting https://github.com/rust-lang/rust/issues/70256.
r? @varkor
Refactorings to get rid of rustc_codegen_utils
r? @eddyb
cc #45276
After this, the only modules left in `rustc_codegen_utils` are
- `link`: a bunch of linking-related functions (many dealing with file names). These are mostly consumed by save analysis, rustc_driver, rustc_interface, and of course codegen. I assume they live here because we don't want a dependency of save analysis on codegen... Perhaps they can be moved to librustc?
- ~`symbol_names` and `symbol_names_test`: honestly it seems odd that `symbol_names_test` is not a submodule of `symbol_names`. It seems like these could honestly live in their own crate or move to librustc. Already name mangling is exported as the `symbol_name` query.~ (move it to its own crate)
I don't mind doing either of the above as part of this PR or a followup if you want.
ast: `Mac`/`Macro` -> `MacCall`
It's now obvious that these refer to macro calls rather than to macro definitions.
It's also a single name instead of two different names in different places.
`rustc_expand` usually calls macro calls in a wide sense (including attributes and derives) "macro invocations", but structures and variants renamed in this PR are only relevant to fn-like macros, so it's simpler and clearer to just call them calls.
cc https://github.com/rust-lang/rust/pull/63586#discussion_r314232513
r? @eddyb
Rename `libsyntax` to `librustc_ast`
This was the last rustc crate that wasn't following the `rustc_*` naming convention.
Follow-up to https://github.com/rust-lang/rust/pull/67763.
parse: allow `type Foo: Ord` syntactically
This addresses:
> (Work still remains to fuse this with free type aliases, but this can be done later.)
in https://github.com/rust-lang/rust/pull/69194.
r? @petrochenkov
parse: fuse associated and extern items up to defaultness
Language changes:
- The grammar of extern `type` aliases is unified with associated ones, and becomes:
```rust
TypeItem = "type" ident generics {":" bounds}? where_clause {"=" type}? ";" ;
```
Semantic restrictions (`ast_validation`) are added to forbid any parameters in `generics`, any bounds in `bounds`, and any predicates in `where_clause`, as well as the presence of a type expression (`= u8`).
(Work still remains to fuse this with free `type` aliases, but this can be done later.)
- The grammar of constants and static items (free, associated, and extern) now permits the absence of an expression, and becomes:
```rust
GlobalItem = {"const" {ident | "_"} | "static" "mut"? ident} {"=" expr}? ";" ;
```
- A semantic restriction is added to enforce the presence of the expression (the body).
- A semantic restriction is added to reject `const _` in associated contexts.
Together, these changes allow us to fuse the grammar of associated items and extern items up to `default`ness which is the main goal of the PR.
-----------------------
We are now very close to fully fusing the entirely of item parsing and their ASTs. To progress further, we must make a decision: should we parse e.g. `default use foo::bar;` and whatnot? Accepting that is likely easiest from a parsing perspective, as it does not require using look-ahead, but it is perhaps not too onerous to only accept it for `fn`s (and all their various qualifiers), `const`s, `static`s, and `type`s.
r? @petrochenkov
