Problem

When generating Zod or Valibot schemas from OpenAPI specs containing regex patterns with forward slashes, the generated TypeScript code was syntactically invalid. Forward slashes inside regex patterns were not being escaped, causing the regex literal to terminate prematurely.

Example issue:

# OpenAPI spec
components:
  schemas:
    base64Image:
      type: string
      pattern: '^data:image/svg\+xml;base64,[A-Za-z0-9+/]+=*$'

Generated invalid code:

export const zBase64Image = z.string().regex(/^data:image/svg\+xml;base64,[A-Za-z0-9+/]+=*$/);
//                                                    ^ This forward slash terminates the regex

This resulted in TypeScript compilation errors and broken generated code.

Solution

Fixed the createRegularExpressionLiteral function in packages/openapi-ts/src/tsc/types.ts to properly escape forward slashes in regex patterns before wrapping them in regex literal syntax.

The fix:

1. Extracts pattern content (removing outer slashes if present)
2. Uses negative lookbehind (?<!\\)/ to escape only unescaped forward slashes, preventing double-escaping
3. Wraps the escaped pattern with forward slashes to create a valid regex literal

Now generates valid code:

export const zBase64Image = z.string().regex(/^data:image\/svg\+xml;base64,[A-Za-z0-9+\/]+=*$/);
//                                                    ^ Forward slashes properly escaped

Impact

• ✅ Fixes Zod schemas for all versions (v3, v4, mini)
• ✅ Fixes Valibot schemas (uses the same underlying function)
• ✅ Backward compatible - existing patterns without forward slashes continue to work unchanged
• ✅ Handles already escaped slashes - prevents double-escaping of patterns that are already correctly escaped
• ✅ No performance impact - only processes patterns when forward slashes are present

Testing

Added comprehensive test coverage with 8 test cases covering:

• Patterns with forward slashes (main issue case)
• Patterns without forward slashes (regression prevention)
• Patterns with multiple forward slashes
• Patterns with existing outer slashes
• Patterns with already correctly escaped slashes (prevents double-escaping)
• Flag preservation
• Edge cases

All existing tests continue to pass, confirming no regressions were introduced.

Fixes #2691

Fixes #2691

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