better-regex: Fix empty-pattern autofix (#2881)

sindresorhus · web-flow · commit c20198770cb4 · 2026-02-14T02:40:31.000+07:00
diff --git a/rules/better-regex.js b/rules/better-regex.js
@@ -10,6 +10,14 @@ const messages = {
 	[MESSAGE_ID_PARSE_ERROR]: 'Problem parsing {{original}}: {{error}}',
 };
 
+// `regexp-tree` can optimize `/|/` into `//`, which is not valid JavaScript syntax.
+// Normalize to an explicit empty alternative so the autofix always stays parseable.
+const normalizeOptimizedRegexLiteral = optimizedRegexLiteral => (
+	optimizedRegexLiteral.startsWith('//')
+		? `/(?:)/${optimizedRegexLiteral.slice(2)}`
+		: optimizedRegexLiteral
+);
+
 /** @param {import('eslint').Rule.RuleContext} context */
 const create = context => {
 	const {sortCharacterClasses} = context.options[0];
@@ -36,6 +44,7 @@ const create = context => {
 
 		try {
 			optimized = regexpTree.optimize(original, undefined, {blacklist: ignoreList}).toString();
+			optimized = normalizeOptimizedRegexLiteral(optimized);
 		} catch (error) {
 			return {
 				node,
diff --git a/test/better-regex.js b/test/better-regex.js
@@ -89,6 +89,26 @@ test({
 			errors: createError(String.raw`/\w/ig`, String.raw`/\w/gi`),
 			output: String.raw`const foo = /\w/gi`,
 		},
+		{
+			code: String.raw`const expression = /|/`,
+			errors: createError(String.raw`/|/`, String.raw`/(?:)/`),
+			output: String.raw`const expression = /(?:)/`,
+		},
+		{
+			code: String.raw`const expression = /|/g`,
+			errors: createError(String.raw`/|/g`, String.raw`/(?:)/g`),
+			output: String.raw`const expression = /(?:)/g`,
+		},
+		{
+			code: String.raw`const expression = /(?:)|/`,
+			errors: createError(String.raw`/(?:)|/`, String.raw`/(?:)/`),
+			output: String.raw`const expression = /(?:)/`,
+		},
+		{
+			code: String.raw`const expression = /(?:)|/g`,
+			errors: createError(String.raw`/(?:)|/g`, String.raw`/(?:)/g`),
+			output: String.raw`const expression = /(?:)/g`,
+		},
 		{
 			code: 'const foo = /[0-9]/',
 			errors: createError('/[0-9]/', String.raw`/\d/`),
