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fix(linter): prevent useConsistentArrowReturn from producing ASI-affected code #8440

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fix(linter): prevent useConsistentArrowReturn from producing ASI-affected code #8440

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5 changes: 5 additions & 0 deletions .changeset/fix-use-consistent-arrow-return-asi.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
"@biomejs/biome": patch
---

Fixed [#8179](https://github.com/biomejs/biome/issues/8179): [`useConsistentArrowReturn`](https://biomejs.dev/linter/rules/use-consistent-arrow-return/) autofix no longer produces semantically incorrect code when adding braces to arrow functions with multiline expressions. Previously, the fix could place a newline between `return` and the expression, triggering JavaScript's automatic semicolon insertion (ASI) and causing the function to return `undefined` instead of the intended value.
5 changes: 5 additions & 0 deletions crates/biome_js_analyze/src/lint/nursery/use_consistent_arrow_return.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -179,6 +179,11 @@ impl Rule for UseConsistentArrowReturn {
expr.clone()
};

// Remove leading trivia (newlines/whitespace) from the expression to prevent
// ASI issues where `return\n expr` would return undefined instead of expr.
// See: https://github.com/biomejs/biome/issues/8179
let expr_to_return = expr_to_return.trim_leading_trivia()?;

let return_statement =
make::js_return_statement(make::token(T![return]).with_trailing_trivia([(
biome_js_syntax::TriviaPieceKind::Whitespace,
Expand Down
9 changes: 9 additions & 0 deletions crates/biome_js_analyze/tests/specs/nursery/useConsistentArrowReturn/always.invalid.js
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Expand Up @@ -2,3 +2,12 @@ const returnsSequenceArrow = () => (a, b)

const returnsAwaitArrow = async () => await fetchData()

// Issue #8179: multiline expressions should not cause ASI issues
const getSchemaRowTypes = (l) =>
l
.split("\n")

const multilineChain = () =>
foo
.bar()
.baz()
99 changes: 85 additions & 14 deletions crates/biome_js_analyze/tests/specs/nursery/useConsistentArrowReturn/always.invalid.js.snap
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Expand Up @@ -8,6 +8,15 @@ const returnsSequenceArrow = () => (a, b)

const returnsAwaitArrow = async () => await fetchData()

// Issue #8179: multiline expressions should not cause ASI issues
const getSchemaRowTypes = (l) =>
l
.split("\n")

const multilineChain = () =>
foo
.bar()
.baz()

```

Expand All @@ -24,12 +33,12 @@ always.invalid.js:1:30 lint/nursery/useConsistentArrowReturn FIXABLE ━━━

i Safe fix: Add braces to the arrow function body.

1 │ - const·returnsSequenceArrow·=·()·=>·(a,·b)
1 │ + const·returnsSequenceArrow·=·()·=>·{
2 │ + → return·a,·b;
3 │ + }
2 4 │
3 5 │ const returnsAwaitArrow = async () => await fetchData()
1 │ - const·returnsSequenceArrow·=·()·=>·(a,·b)
1 │ + const·returnsSequenceArrow·=·()·=>·{
2 │ + → return·a,·b;
3 │ + }
2 4 │
3 5 │ const returnsAwaitArrow = async () => await fetchData()


```
Expand All @@ -44,17 +53,79 @@ always.invalid.js:3:27 lint/nursery/useConsistentArrowReturn FIXABLE ━━━
> 3 │ const returnsAwaitArrow = async () => await fetchData()
│ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
4 │
5 │ // Issue #8179: multiline expressions should not cause ASI issues

i Safe fix: Add braces to the arrow function body.

1 1 │ const returnsSequenceArrow = () => (a, b)
2 2 │
3 │ - const·returnsAwaitArrow·=·async·()·=>·await·fetchData()
3 │ + const·returnsAwaitArrow·=·async·()·=>·{
4 │ + → return·await·fetchData();
5 │ + }
4 6 │
5 7 │ // Issue #8179: multiline expressions should not cause ASI issues


```

```
always.invalid.js:6:27 lint/nursery/useConsistentArrowReturn FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

! This arrow function body should be a block statement.

5 │ // Issue #8179: multiline expressions should not cause ASI issues
> 6 │ const getSchemaRowTypes = (l) =>
│ ^^^^^^
> 7 │ l
> 8 │ .split("\n")
│ ^^^^^^^^^^^^
9 │
10 │ const multilineChain = () =>

i Safe fix: Add braces to the arrow function body.

5 5 │ // Issue #8179: multiline expressions should not cause ASI issues
6 6 │ const getSchemaRowTypes = (l) =>
7 │ - ··l
8 │ - ····.split("\n")
7 │ + ··{
8 │ + → return·l
9 │ + ····.split("\n");
10 │ + }
9 11 │
10 12 │ const multilineChain = () =>


```

```
always.invalid.js:10:24 lint/nursery/useConsistentArrowReturn FIXABLE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━

! This arrow function body should be a block statement.

8 │ .split("\n")
9 │
> 10 │ const multilineChain = () =>
│ ^^^^^
> 11 │ foo
> 12 │ .bar()
> 13 │ .baz()
│ ^^^^^^
14 │

i Safe fix: Add braces to the arrow function body.

1 1 │ const returnsSequenceArrow = () => (a, b)
2 2 │
3 │ - const·returnsAwaitArrow·=·async·()·=>·await·fetchData()
3 │ + const·returnsAwaitArrow·=·async·()·=>·{
4 │ + → return·await·fetchData();
5 │ + }
4 6 │
5 7 │
9 9 │
10 10 │ const multilineChain = () =>
11 │ - ··foo
11 │ + ··{
12 │ + → return·foo
12 13 │ .bar()
13 │ - ····.baz()
14 │ + ····.baz();
15 │ + }
14 16 │


```