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fix(linter/prefer-array-flat-map): error for .flat(1.0) #12360

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Merged
merged 1 commit into from
Jul 17, 2025
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fix(linter/prefer-array-flat-map): error for .flat(1.0) #12360

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26 changes: 20 additions & 6 deletions crates/oxc_linter/src/rules/unicorn/prefer_array_flat_map.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -68,11 +68,13 @@ impl Rule for PreferArrayFlatMap {
}

if let Some(first_arg) = flat_call_expr.arguments.first() {
if let Argument::NumericLiteral(number_lit) = first_arg {
if number_lit.raw.as_ref().unwrap() != "1" {
return;
}
} else {
// `Array.prototype.flat` rounds down the argument.
// So `.flat(1.5)` is equivalent to `.flat(1)`.
// https://tc39.es/ecma262/#sec-array.prototype.flat
// https://tc39.es/ecma262/#sec-tointegerorinfinity
// https://tc39.es/ecma262/#eqn-truncate
#[expect(clippy::float_cmp)]
if !matches!(first_arg, Argument::NumericLiteral(lit) if lit.value.floor() == 1.0) {
return;
}
}
Expand Down Expand Up @@ -107,7 +109,13 @@ fn test() {
("const bar = [[1],[2],[3]].flat()", None),
("const bar = [1,2,3].map(i => [i]).sort().flat()", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(2)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(2.0)", None),
// Parsed as 0.9999999999999999. Rounds down to 0.
("const bar = [[1],[2],[3]].map(i => [i]).flat(0.99999999999999994)", None),
// Parsed as 2.0.
("const bar = [[1],[2],[3]].map(i => [i]).flat(1.99999999999999989)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(1, null)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(-1)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(Infinity)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(Number.POSITIVE_INFINITY)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(Number.MAX_VALUE)", None),
Expand All @@ -117,11 +125,17 @@ fn test() {
("const bar = [[1],[2],[3]].map(i => [i]).flat(+1)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(foo)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(foo.bar)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(1.00)", None),
];

let fail = vec![
("const bar = [[1],[2],[3]].map(i => [i]).flat()", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(1)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(1.0)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(1.00)", None),
// Parsed as 1.0.
("const bar = [[1],[2],[3]].map(i => [i]).flat(0.99999999999999995)", None),
// Parsed as 1.9999999999999998. Rounds down to 1.
("const bar = [[1],[2],[3]].map(i => [i]).flat(1.99999999999999988)", None),
("const bar = [[1],[2],[3]].map(i => [i]).flat(1,)", None),
("const bar = [1,2,3].map(i => [i]).flat()", None),
("const bar = [1,2,3].map((i) => [i]).flat()", None),
Expand Down
35 changes: 35 additions & 0 deletions crates/oxc_linter/src/snapshots/unicorn_prefer_array_flat_map.snap
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,41 @@ source: crates/oxc_linter/src/tester.rs
╰────
help: Prefer `.flatMap(…)` over `.map(…).flat()`.

⚠ eslint-plugin-unicorn(prefer-array-flat-map): `Array.flatMap` performs `Array.map` and `Array.flat` in one step.
╭─[prefer_array_flat_map.tsx:1:13]
1 │ const bar = [[1],[2],[3]].map(i => [i]).flat(1)
· ───────────────────────────────────
╰────
help: Prefer `.flatMap(…)` over `.map(…).flat()`.

⚠ eslint-plugin-unicorn(prefer-array-flat-map): `Array.flatMap` performs `Array.map` and `Array.flat` in one step.
╭─[prefer_array_flat_map.tsx:1:13]
1 │ const bar = [[1],[2],[3]].map(i => [i]).flat(1.0)
· ─────────────────────────────────────
╰────
help: Prefer `.flatMap(…)` over `.map(…).flat()`.

⚠ eslint-plugin-unicorn(prefer-array-flat-map): `Array.flatMap` performs `Array.map` and `Array.flat` in one step.
╭─[prefer_array_flat_map.tsx:1:13]
1 │ const bar = [[1],[2],[3]].map(i => [i]).flat(1.00)
· ──────────────────────────────────────
╰────
help: Prefer `.flatMap(…)` over `.map(…).flat()`.

⚠ eslint-plugin-unicorn(prefer-array-flat-map): `Array.flatMap` performs `Array.map` and `Array.flat` in one step.
╭─[prefer_array_flat_map.tsx:1:13]
1 │ const bar = [[1],[2],[3]].map(i => [i]).flat(0.99999999999999995)
· ─────────────────────────────────────────────────────
╰────
help: Prefer `.flatMap(…)` over `.map(…).flat()`.

⚠ eslint-plugin-unicorn(prefer-array-flat-map): `Array.flatMap` performs `Array.map` and `Array.flat` in one step.
╭─[prefer_array_flat_map.tsx:1:13]
1 │ const bar = [[1],[2],[3]].map(i => [i]).flat(1.99999999999999988)
· ─────────────────────────────────────────────────────
╰────
help: Prefer `.flatMap(…)` over `.map(…).flat()`.

⚠ eslint-plugin-unicorn(prefer-array-flat-map): `Array.flatMap` performs `Array.map` and `Array.flat` in one step.
╭─[prefer_array_flat_map.tsx:1:13]
1 │ const bar = [[1],[2],[3]].map(i => [i]).flat(1,)
Expand Down
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