biome complexity/noAdjacentSpacesInRegex: fix changes program behavior

Hypothesis Nemotron 3 Super predicted to fire fired 1×

Interferes with source inspection or debugging where the original literal's space count is logged or compared.

Program

Output

4

2

Judge Nemotron 3 Ultra advisory introspection-only · low

The fix rewrites the regex literal from /a b c/ to /a {2}b {2}c/, which changes the value of RegExp.prototype.source. The program only inspects this source text by splitting on spaces and counting them, so the behavioral difference is purely introspection of the rewritten literal itself.

Explanation Nemotron 3 Super unverified

The original regex literal `/a b c/` contains two spaces between each letter; its `.source` property returns the exact string `"a b c"`. Splitting this on single spaces yields `["a", "", "b", "", "c"]`, length 5, minus 1 gives 4. The rewritten regex `/a {2}b {2}c/` uses the quantifier `{2}` to match exactly two spaces, but its `.source` is `"a {2}b {2}c"`. Splitting that on spaces produces `["a", "{2}b", "{2}c"]`, length 3, minus 1 equals 2. Thus the change alters the literal text of the regex source, affecting the subsequent string operation and output.

Reproduce

file

prog.js (the before program)

minimized program

r1-p008.js

evidence sheet

r1-p008.md

regression fixture

r1-p008.js the minimized program with a header stating the observed change, for the tool's test suite

node prog.js
bunx @biomejs/biome lint --only=complexity/noAdjacentSpacesInRegex --write prog.js
node prog.js

Upstream search GitHub issues Tavily Nemotron 3 Super + Ultra

noAdjacentSpacesInRegex fix · complexity noAdjacentSpacesInRegex regex literal · regex adjacent spaces curly braces replacement · Biome lint rule spacing in pattern

• duplicate biomejs/biome/issues/11419 same rule noAdjacentSpacesInRegex corrupting regex by replacing spaces with quantifiers, same defect class
• related biomejs/biome/issues/6670 lists complexity/noAdjacentSpacesInRegex among many rules but no specific defect

Details

program

Source Inspection or Debugging Interference

hazard

Interferes with source inspection or debugging where the original literal's space count is logged or compared.

oracle

stdout before: 4 stdout after: 2

run

2026-10-17T20-03-48-850Z-01ch-biome-complexity_noAdjacentSpacesInRegex

--- orig.js	2026-10-17 16:03:58.947281645 -0400
+++ fixed.js	2026-10-17 16:03:59.213263777 -0400
@@ -1,2 +1,2 @@
-const re = /a  b  c/;
+const re = /a {2}b {2}c/;
 console.log(re.source.split(' ').length - 1);

Summary

- Name: noAdjacentSpacesInRegex
- Fix: safe
- Default severity: warn
- Available from version: 1.0.0
- Diagnostic category: lint/complexity/noAdjacentSpacesInRegex
- This rule is recommended

Description

 Disallow unclear usage of consecutive space characters in regular expression literals

Examples

Invalid

 ```js,expect_diagnostic
 /   /
 ```

 ```js,expect_diagnostic
 /foo  */
 ```

 ```js,expect_diagnostic
 /foo  {2,}bar   {3,5}baz/
 ```

 ```js,expect_diagnostic
 /foo [ba]r  b(a|z)/
 ```

Valid

 ```js
 /foo {2}bar/
```

 ```js
 / foo bar baz /
```

 ```js
 /foo bar	baz/
```