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
This commit reduces the size of `Nonterminal` from a whopping 240 bytes
to 72 bytes (on x86-64), which gets it below the `memcpy` threshold.
It also removes some impedance mismatches with `Annotatable`, which
already uses `P` for these variants.
```
error[E0412]: cannot find type `T` in this scope
--> file.rs:3:12
|
3 | impl Trait<T> for Struct {}
| - ^ not found in this scope
| |
| help: you might be missing a type parameter: `<T>`
```
Fix#64298.
Nix reexports from `rustc_span` in `syntax`
Remove reexports `syntax::{source_map, symbol, edition}` and use `rustc_span` paths directly.
r? @petrochenkov
Suggest calling method when first argument is `self`
Closes: #66782
I've explored different approaches for this MR but I think the most straightforward is the best one.
I've tried to find out if the methods for given type exist (to maybe have a better suggestion), but we don't collect them anywhere and collecting them is quite problematic. Moreover, collecting all the methods would require rewriting big part of the code and also could potentially include performance degradation, which I don't think is necessary for this simple case.
Make GATs less ICE-prone.
After this PR simple lifetime-generic associated types can now be used in a compiling program. There are two big limitations:
* #30472 has not been addressed in any way (see src/test/ui/generic-associated-types/iterable.rs)
* Using type- and const-generic associated types errors because bound types and constants aren't handled by trait solving.
* The errors are technically non-fatal, but they happen in a [part of the compiler](4abb0ad273/src/librustc_typeck/lib.rs (L298)) that fairly aggressively stops compiling on errors.
closes#47206closes#49362closes#62521closes#63300closes#64755closes#67089
A path type argument could be a generic const argument due to
limitations as to what we can determine at parsing. We double check just
to be sure by trying to resolve in the type namespace first, and if that
fails we try again in the value namespace. If resolution in the value
namespace succeeds, we have a generic const argument on our hands.
Push `ast::{ItemKind, ImplItemKind}::OpaqueTy` hack down into lowering
We currently have a hack in the form of `ast::{ItemKind, ImplItemKind}::OpaqueTy` which is constructed literally when you write `type Alias = impl Trait;` but not e.g. `type Alias = Vec<impl Trait>;`. Per https://github.com/rust-lang/rfcs/pull/2515, this needs to change to allow `impl Trait` in nested positions. This PR achieves this change for the syntactic aspect but not the semantic one, which will require changes in lowering and def collection. In the interim, `TyKind::opaque_top_hack` is introduced to avoid knock-on changes in lowering, collection, and resolve. These hacks can then be removed and fixed one by one until the desired semantics are supported.
r? @varkor
`MethodSig` -> `FnSig` & Use it in `ItemKind::Fn`
In both AST & HIR, rename `MethodSig` to `FnSig` and then proceed to use it in `ItemKind::Fn` so that the overall structure is more regular.
r? @davidtwco
