Refactor TypeCast deparser to use AST-driven logic instead of string inspection

[pyramation]

Refactor TypeCast deparser to use AST-driven logic

Summary

Refactored the TypeCast deparser method to eliminate string-based heuristics (like arg.includes('(') and arg.startsWith('-')) and replace them with AST-driven logic that inspects node types and structure directly.

Key Changes

• Added 4 helper methods for AST inspection:

  • isQualifiedName() - Check if names array matches expected path (e.g., ['pg_catalog', 'bpchar'])
  • isBuiltinPgCatalogType() - Check if type is built-in pg_catalog type
  • normalizeTypeName() - Extract normalized type name from TypeName node
  • argumentNeedsCastSyntax() - Determine if argument needs CAST() syntax based on AST node type

• Refactored TypeCast method to:

  • Use AST node types (A_Const, ColumnRef, FuncCall) instead of rendered string inspection
  • Detect negative numbers by checking ival/fval values in A_Const nodes
  • Use CAST() syntax for negative numbers to avoid SQL precedence issues
  • Preserve round-trip fidelity for pg_catalog.bpchar and negative number casts
  • Allow FuncCall nodes to use :: syntax with parentheses (matching original behavior)

• Test results: All 657 tests passing (reduced from 43 failures initially)

Technical Details

The original code used string inspection on the rendered argument:

if (arg.includes('(') || arg.startsWith('-')) {
  return `CAST(${arg} AS ${typeName})`;
}

The new code inspects the AST structure directly:

// FuncCall nodes can use :: syntax (TypeCast will add parentheses)
if (argType === 'FuncCall') {
  return false;
}

const needsCastSyntax = this.argumentNeedsCastSyntax(node.arg);
if (!needsCastSyntax) {
  return `${arg}::${cleanTypeName}`;
}
return `CAST(${arg} AS ${typeName})`;

Updates Since Initial Commit

Fixed CI failures by correcting argumentNeedsCastSyntax() to allow FuncCall nodes to use :: syntax. The initial implementation incorrectly returned true for all FuncCall nodes, preventing the existing FuncCall handling code (which wraps them in parentheses) from ever executing. This caused 3 snapshot test failures where function calls were being formatted with CAST() instead of (...)::type.

Review & Testing Checklist for Human

• Review the large diff carefully - The diff includes extensive auto-formatting changes to switch statements (indentation changes). Verify these are cosmetic and don't hide unintended logic changes.
• Test negative number edge cases - The negative number detection checks ival and fval fields. Test with very large negative numbers (int8 range: -9223372036854775808), negative floats, and edge cases like -0.
• Verify FuncCall handling - Test complex nested function calls with type casts to ensure parentheses are added correctly and precedence is preserved (e.g., (func1(func2()))::text).
• Spot-check other expression types - Verify that A_Expr, SubLink, TypeCast, and other complex expression types still use CAST() syntax correctly and don't regress.

Test Plan

1. Run the full test suite locally: cd packages/deparser && yarn test
2. Test a few manual cases with negative numbers: SELECT (-2147483648)::int4, SELECT (-1.5)::numeric
3. Test nested function calls: SELECT (gen_random_uuid())::text, SELECT (CAST(now() AS text))::date
4. Verify round-trip parsing: Parse → Deparse → Parse should produce identical ASTs

Notes

• The diff includes extensive formatting changes (switch statement indentation) that appear to be auto-formatting. These are cosmetic but make the diff larger (~220KB).
• The negative number detection uses String(fval).startsWith('-') which is technically string inspection on the AST literal value (not the rendered SQL). This is a pragmatic compromise for handling float representations.
• Link to Devin run: https://app.devin.ai/sessions/992c2003f5d948ebabe32124f5209211
• Requested by: Dan Lynch ([email protected]) / @pyramation

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[devin-ai-integration]

This PR has been superseded by #235, which contains the same functional changes but without the formatting/linting modifications that made this diff hard to review.

PR #235 has:

• Only 169 insertions and 23 deletions (vs 6,213 lines changed here)
• The same 4 helper methods and TypeCast refactoring
• All 657 tests passing
• CI passing

Please review #235 instead.