trait alias infrastructure
This will be an implementation of trait aliases (RFC 1733, #41517).
Progress so far:
- [x] Feature gate
- [x] Add to parser
- [x] `where` clauses
- [x] prohibit LHS type parameter bounds via AST validation https://github.com/rust-lang/rust/pull/45047#discussion_r143575575
- [x] Add to AST and HIR
- [x] make a separate PathSource for trait alias contexts https://github.com/rust-lang/rust/pull/45047#discussion_r143353932
- [x] Stub out enough of typeck and resolve to just barely not ICE
Postponed:
- [ ] Actually implement the alias part
- [ ] #21903
- [ ] #24010
I need some pointers on where to start with that last one. The test currently does this:
```
error[E0283]: type annotations required: cannot resolve `_: CD`
--> src/test/run-pass/trait-alias.rs:34:16
|
34 | let both = foo();
| ^^^
|
= note: required by `foo`
```
macros: hygienize use of `core`/`std` in builtin macros
Today, if a builtin macro wants to access an item from `core` or `std` (depending `#![no_std]`), it generates `::core::path::to::item` or `::std::path::to::item` respectively (c.f. `fn std_path()` in `libsyntax/ext/base.rs`).
This PR refactors the builtin macros to instead always emit `$crate::path::to::item` here. That is, the def site of builtin macros is taken to be in `extern crate core;` or `extern crate std;`. Since builtin macros are macros 1.0 (i.e. mostly unhygienic), changing the def site can only effect the resolution of `$crate`.
r? @nrc
Modify message for keyword as identifier name
This is a temporary solution to #46311.
The message is generic enough to cover both cases and is probably a fine enough solution to the specific problem described in the task. However, the underlying reason for this to be wrong is that `next_token_inner` returns `Lifetime` even if the token is a label. That's not simple, as the syntax for both can be quite similar and it may need to take a look to the next token to make a decision. I'm not sure I have enough knowledge about the project to be able to solve that (yet!), so I thought I'll fix the immediate problem first.
Add case insensitive comparison, besides Levenstein for DYM
Closes#46332
Draft version. The idea is that Levenstein does not work for some cases when we have multiple equal weights for strings. I didn't understand the case with `if found != name => Some(found)` so it means that new code does not work correctly yet.
At least now I think that we might return all maximal weights from levenstein and think about next cases in priority order:
1) There is exact match -> None
2) There is exact match, but case insensitive -> Some(match)
3) There is some match from levenstein -> Some(matches.take_any)
4) There is no match -> None
@estebank WDYT?
Generic Associated Types Parsing & Name Resolution
Hi!
This PR adds parsing for generic associated types! 🎉🎉🎉
Tracking Issue: #44265
## Notes For Reviewers
* [x] I still need to add the stdout and stderr files to my ui tests. It takes me a *long* time to compile the compiler locally, so I'm going to add this as soon as possible in the next day or so.
* [ ] My current ui tests aren't very good or very thorough. I'm reusing the `parse_generics` and `parse_where_clause` methods from elsewhere in the parser, so my changes work without being particularly complex. I'm not sure if I should duplicate all of the generics test cases for generic associated types. It might actually be appropriate to duplicate everything here, since we don't want to rely on an implementation detail in case it changes in the future. If you think so too, I'll adapt all of the generics test cases into the generic associated types test cases.
* [ ] There is still more work required to make the run-pass tests pass here. In particular, we need to make the following errors disappear:
```
error[E0110]: lifetime parameters are not allowed on this type
--> ./src/test/run-pass/rfc1598-generic-associated-types/streaming_iterator.rs:23:41
|
23 | bar: <T as StreamingIterator>::Item<'static>,
| ^^^^^^^ lifetime parameter not allowed on this type
```
```
error[E0261]: use of undeclared lifetime name `'a`
--> ./src/test/run-pass/rfc1598-generic-associated-types/iterable.rs:15:47
|
15 | type Iter<'a>: Iterator<Item = Self::Item<'a>>;
| ^^ undeclared lifetime
```
There is a FIXME comment in streaming_iterator. If you uncomment that line, you get the following:
```
error: expected one of `!`, `+`, `,`, `::`, or `>`, found `=`
--> ./src/test/run-pass/rfc1598-generic-associated-types/streaming_iterator.rs:29:45
|
29 | fn foo<T: for<'a> StreamingIterator<Item<'a>=&'a [i32]>>(iter: T) { /* ... */ }
| ^ expected one of `!`, `+`, `,`, `::`, or `>` here
```
r? @nikomatsakis
The previous method ran into problems because ICH would treat Spans
as (file,line,col) but the cache contained byte offsets and its
possible for the latter to change while the former stayed stable.
Remove semicolon note
In reference to issue #46186
r? @estebank
First time doing a pull request, if there are any suggestions on how to improve this please let me know.
@jjolly
When encountering `pub ident`, attempt to identify the code that comes
afterwards, wether it is a brace block (assume it is a struct), a paren
list followed by a colon (assume struct) or a paren list followed by a
block (assume a fn). Consume those blocks to avoid any further parser
errors and return a `Placeholder` item in order to allow the parser to
continue. In the case of unenclosed blocks, the behavior is the same as
it is currently: no further errors are processed.
