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fix(linter/prefer-const): replace entire declaration over just the let kw #18814

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Merged
graphite-app merged 1 commit into from
Feb 1, 2026
Merged

fix(linter/prefer-const): replace entire declaration over just the let kw #18814

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24 changes: 15 additions & 9 deletions crates/oxc_linter/src/rules/eslint/prefer_const.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -213,14 +213,18 @@ impl PreferConst {
if !is_for_in_of_init && decl.declarations.iter().any(|d| d.init.is_none()) {
return fixer.noop();
}
// calculate location of `let` keyword
// Replace the entire declaration span to prevent conflicts with other rules
// (e.g., no-useless-undefined) that might also modify this declaration.
// By replacing the full span, overlapping fixes will conflict and only one will be applied.
let decl_span = decl.span();
let decl_text = decl_span.source_text(ctx.source_text());
#[expect(clippy::cast_possible_truncation)]
let let_span = decl_text.find("let").map(|start| {
Span::new(decl_span.start + start as u32, decl_span.start + start as u32 + 3)
});
if let Some(let_span) = let_span { fixer.replace(let_span, "const") } else { fixer.noop() }

if let Some(let_pos) = decl_text.find("let") {
let new_text = format!("{}const{}", &decl_text[..let_pos], &decl_text[let_pos + 3..]);
fixer.replace(decl_span, new_text)
} else {
fixer.noop()
}
}

/// Check if an assignment target contains any member expressions (recursively)
Expand Down Expand Up @@ -1022,10 +1026,12 @@ fn test() {
None,
),
(
// The original ESLint rule requires 2 passes to get the correct fix here, while
// we compare to the final fixed output directly.
// We should also be fixing the inner `let` to `const`.
// But to avoid conflicting with other fixers, we replace the entire statement.
// This means the user would have to run oxlint --fix multiple times to get all fixes.
// But that's better than the alternative (partial fixes causing syntax errors).
"let someFunc = () => { let a = 1, b = 2; foo(a, b) }",
"const someFunc = () => { const a = 1, b = 2; foo(a, b) }",
"const someFunc = () => { let a = 1, b = 2; foo(a, b) }",
None,
),
("let foo = undefined;", "const foo = undefined;", None),
Expand Down
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