Problem

When generating Zod and Valibot validators from OpenAPI specs, backslash characters in regex patterns were not being correctly escaped, causing the generated regex to incorrectly allow backslash characters that should have been excluded.

For example, with this OpenAPI pattern:

{
  "pattern": "^[^.][^\\/:*?\"<>| ]*$"
}

The generated validator was:

z.string().regex(/^[^.][^\/:*?"<>| ]*$/)  // ❌ Allows backslashes

But should have been:

z.string().regex(/^[^.][^\\/:*?"<>| ]*$/)  // ✅ Correctly excludes backslashes

This violated ESLint's no-useless-escape rule and more importantly, failed to properly validate strings containing backslash characters.

Root Causes

1. Incorrect logic in createRegularExpressionLiteral()

The function used a negative lookbehind (?<!\\) to avoid double-escaping forward slashes. However, when getPattern() doubles backslashes (e.g., \ becomes \\ in the string), patterns like \\/ were incorrectly treated as already-escaped forward slashes, when they actually represented a literal backslash followed by an unescaped forward slash.

2. Missing getPattern() calls in IR parsers

The newer IR-based parsers (3.0.x and 3.1.x) were directly assigning schema.pattern without calling getPattern() to escape backslashes for string literals, unlike the older v2/v3 parsers.

Solution

1. Updated createRegularExpressionLiteral() to check if a forward slash is immediately preceded by any backslash character. If so, the forward slash is kept as-is since it's part of the regex pattern (not needing escape in that context).

2. Added getPattern() calls in both 3.0.x/parser/schema.ts and 3.1.x/parser/schema.ts to ensure backslashes are properly doubled for regex literals.

3. Added comprehensive tests to verify the fix handles various backslash scenarios correctly.

4. Updated all validator test snapshots (48 files total: 42 Zod + 6 Valibot) with the corrected regex patterns.

Testing

• ✅ All 905 existing tests pass
• ✅ All 66 Zod v3 tests pass with updated snapshots
• ✅ All 66 Zod v4 tests pass with updated snapshots
• ✅ All 550 main tests pass with updated Valibot snapshots
• ✅ Manual verification with reproduction case from the issue

The fix applies to both Zod and Valibot validators since both use the same createRegularExpressionLiteral() function.

Fixes #2733

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