Rust: False positive for unused variable names
Nobody has claimed this yet.
Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 38/100
Research direction
Start with the linked code-scanning alert and the Rust snippet, then trace the CodeQL Rust unused-variable query's handling of format! interpolation. Done means the query no longer reports name as unused while still detecting genuinely unused variables.
Written by the indexing model from the issue text.
Description
Description of the false positive
CodeQL seems to produce false positives for Rust variables in format strings.
Code samples or links to source code
On 2026-08-13, the folllowing Rust snippet got flagged by CodeQL on https://github.com/alltheplaces/osm-diffs/pull/660. CodeQL posted a notice, claiming Variable 'name' is not used. However, the variable does get used in this snippet, via a format! macro. We also check for unused variables with clippy, which does not flag an unused variable for this code. So, this looks like a false positive from CodeQL.
let producers: Vec<_> = sources
.into_iter()
.map(|(name, reader)| {
let tx = tx.clone();
s.spawn(move || -> Result<()> {
for record in reader.iter()? {
let bytes = record?;
let fti = FeatureToIndex::decode(bytes.as_slice()).with_context(|| {
format!("failed to decode a FeatureToIndex record from {name}")
})?;
tx.send(fti)?;
progress_bar.inc(1);
}
Ok(())
})
})
.collect();
URL to the alert on GitHub code scanning (optional)
https://github.com/alltheplaces/osm-diffs/security/code-scanning/30
- Dominant language
- CodeQL
- Stars
- 10.1k
- Forks
- 2.1k
- Avg merge
- 2d 10h
- Merged PRs (30d)
- 134
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
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- Open a pull request that references the issue number.
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