rust-lang / rust-lang/rust-analyzer

Macro parser did not remove fragment correctly

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A-macro C-bug
Dominant language
Rust
Stars
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Forks
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Avg merge
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Merged PRs (30d)
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Description

rust-analyzer version: rust-analyzer 1.88.0-nightly (a15cce2 2025-04-17)

rustc version: rustc 1.88.0-nightly (a15cce269 2025-04-17)

editor or extension: VIM-9.1

code snippet to reproduce:

use proc_macro_impl::remove_fragment;

macro_rules! foo {
    (1+2) => {};
}
macro_rules! pack {
    ($e:expr) => {
        remove_fragment!(foo!($e))
    };
}

fn main() {
    pack!(1+2);
}
use proc_macro::*;
#[proc_macro]
pub fn remove_fragment(stream: TokenStream) -> TokenStream {
    stream.into_iter().map(|tt| {
        match tt {
            TokenTree::Group(g) => {
                let mut out = Group::new(g.delimiter(), remove_fragment(g.stream()));
                out.set_span(g.span());
                out.into()
            }
            _ => tt,
        }
    }).collect()
}

cargo build 0 errors

rust-analyzer.expandMacro:

// Recursive expansion of pack!! macro
// ====================================

Expansion had errors:
expected literal: `1`

Contributor guide

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First steps

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the rust-analyzer.expandMacro entry point and the minimal Rust reproduction in the issue, comparing its output with the successful cargo build. Trace how remove_fragment! handles the 1+2 token fragment during recursive pack! expansion; done when the macro expands without the expected literal error.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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