rust-lang / rust-lang/rust-analyzer
Macro expansion involving identifiers in parentheses preceded by visibility is broken
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- Rust
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Description
The following snippet does not expand the macro foo! correctly:
fn main() {}
macro_rules! foo {
($a:vis ($b:ident)) => {
pub const X: &str = stringify!($b);
};
}
foo!(
pub (bar)
);
Instead of expanding to
pub const X: &str = "bar"
it expands to
pub const X: &str = "$ b"
It seems that rust-analyzer puts a space between the $ and the b before substituting the macro variables, resulting in a wrong expansion. rustc handles this expansion correctly.
rust-analyzer version: rust-analyzer version: 0.3.1641-standalone (144526c90 2023-08-28) [I have also tried rust-analyzer version: 0.4.1644-standalone (321334429 2023-08-30)]
rustc version: rustc 1.74.0-nightly (84a9f4c6e 2023-08-29)
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the supplied macro_rules! example in rust-analyzer and compare its expansion with rustc. Trace the macro expansion path involved in visibility followed by a parenthesized identifier; done means foo!(pub (bar)) expands to a constant whose string value is "bar", without the inserted space.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 45/100