Implement automatic E-prefix detection for escaped string literals

[devin-ai-integration]

Implement automatic E-prefix detection for escaped string literals in PostgreSQL

Problem

The deparser was not automatically adding the E prefix to string literals containing backslash escape sequences, which is required for proper PostgreSQL syntax when standard_conforming_strings=on (the default since PostgreSQL 9.1).

Solution

Implemented automatic E-prefix detection logic that:

1. Detects escape sequences - Identifies strings containing backslash escape patterns that require E-prefix
2. Adds E-prefix automatically - Enhances string literal generation to include E'...' syntax when needed
3. Proper escaping - Correctly escapes backslashes and quotes within E-prefixed strings
4. Avoids conflicts - Prevents E-prefix for hexadecimal bytea literals to avoid syntax conflicts

Technical Implementation

New needsEscapePrefix() method

needsEscapePrefix(value: string): boolean {
  // Don't add E-prefix to hexadecimal bytea literals (e.g., \xDeAdBeEf)
  if (/^\\x[0-9a-fA-F]+$/i.test(value)) {
    return false;
  }
  
  // Don't add E-prefix to strings that look like bytea literals with mixed content
  if (/\\x[0-9a-fA-F]/.test(value) && !/\\[nrtbf\\']/.test(value)) {
    return false;
  }
  
  // Check for common backslash escape sequences that require E-prefix
  return /\\[nrtbf\\']/.test(value) ||             // Basic escapes: \n, \t, \r, \b, \f, \\, \'
         /\\u[0-9a-fA-F]{4}/.test(value) ||        // Unicode escapes: \u0041
         /\\U[0-9a-fA-F]{8}/.test(value) ||        // Extended unicode escapes: \U00000041
         /\\[0-7]{1,3}/.test(value);               // Octal escapes: \123
}

Enhanced string processing

• A_Const method - Updated to detect escape sequences and apply E-prefix with proper escaping
• String method - Enhanced to handle E-prefix detection in string literal contexts
• Proper escaping - Backslashes are escaped as \\\\ and quotes as '' in E-prefixed strings

Examples

Input AST string values:

• "a\bcd" → E'a\\bcd'
• "a\b'cd" → E'a\\b''cd'
• "ab\'cd" → E'ab\\''cd'
• "\\" → E'\\\\'

Regular strings without escapes:

• "hello world" → 'hello world' (no E-prefix needed)

Testing

• ✅ All 251 test suites pass (264 total tests)
• ✅ Verified E-prefix detection works correctly for various escape patterns
• ✅ Confirmed no regressions in existing functionality
• ✅ Tested reparsing of generated SQL to ensure validity

PostgreSQL Compatibility

This implementation follows PostgreSQL's string literal syntax requirements:

• E-prefix is added for strings with backslash escape sequences
• Proper escaping prevents syntax errors
• Compatible with standard_conforming_strings=on (default since PostgreSQL 9.1)
• Avoids conflicts with bytea literal syntax

---

Link to Devin run: https://app.devin.ai/sessions/53c6e39590e9403ab99a25afe0dd5e99

Requested by: Dan Lynch ([email protected])

[devin-ai-integration]

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