4178: Validate the location of `crate` in paths r=matklad a=djrenren
**This solution does not fully handle `use` statements. See below**
This pull requests implements simple validation of usages of the `crate` keyword in `Path`s. Specifically it validates that:
- If a `PathSegment` is starts with the `crate` keyword, it is also the first segment of the `Path`
- All other usages of `crate` in `Path`s are considered errors.
This aligns with `rustc`'s rules. Unlike rustc this implementation does not issue a special error message in the case of `::crate` but it does catch the error.
Furthermore, this change does not cover all error cases. Specifically the following is not caught:
```rust
use foo::{crate}
```
This is because this check is context sensitive. From an AST perspective, `crate` is the root of the `Path`. Only by inspecting the full `UseItem` do we see that it is not in fact the root. This problem becomes worse because `UseTree`s are allowed to be arbitrarily nested:
```rust
use {crate, {{crate, foo::{crate}}}
```
So this is a hard problem to solve without essentially a breadth-first search. In a traditional compiler, I'd say this error is most easily found during the AST -> HIR conversion pass but within rust-analyzer I'm not sure where it belongs.
Under the implementation in this PR, such errors are ignored so we're *more correct* just not *entirely correct*.
Co-authored-by: John Renner <john@jrenner.net>
todo!() "Indicates unfinished code" (https://doc.rust-lang.org/std/macro.todo.html)
Rust documentation provides further clarification:
> The difference between unimplemented! and todo! is that while todo!
> conveys an intent of implementing the functionality later and the
> message is "not yet implemented", unimplemented! makes no such claims.
todo!() seems more appropriate for assists that insert missing impls.
- Adds a new AstElement trait that is implemented by all generated
node, token and enum structs
- Overhauls the code generators to code-generate all tokens, and
also enhances enums to support including tokens, node, and nested
enums
We treat macro calls as expressions (there's appropriate Into impl),
which causes problem if there's expresison and non-expression macro in
the same node (like in the match arm).
We fix this problem by nesting macor patterns into another node (the
same way we nest path into PathExpr or PathPat). Ideally, we probably
should add a similar nesting for macro expressions, but that needs
some careful thinking about macros in blocks: `{ am_i_expression!() }`.
