Fix async forEach bug in test framework that prevented error catching

Problem

The test framework in packages/deparser/test-utils/index.ts had a critical async/await bug at line 100 where tree.stmts.forEach(async (stmt: any) => { was used. This prevented proper error catching because forEach doesn't wait for async operations - errors thrown inside the async callback were "fire-and-forget" and never bubbled up to fail tests.

Root Cause

// BROKEN: forEach doesn't await async operations
tree.stmts.forEach(async (stmt: any) => {
  // async operations that can throw errors
  const reparsed = await parse(outSql);
  // errors thrown here were never caught
});

This meant that even when the deparser generated invalid SQL that failed to reparse, the test framework couldn't catch these failures and tests would incorrectly pass.

Solution

Fixed the async forEach bug by converting to a proper for-of loop:

// FIXED: for-of properly awaits async operations
for (const stmt of tree.stmts) {
  // async operations that can throw errors
  const reparsed = await parse(outSql);
  // errors are now properly caught and bubble up
}

Also fixed a TypeScript error with the diff function by adding null handling.

Verification

The fix is verified by running the test that was previously passing incorrectly:

Before fix: Test passed silently even with deparser generating invalid SQL
After fix: Test now properly fails with detailed error output:

❌ INVALID_DEPARSED_SQL: misc/launchql-ext-types-1.sql
📥 INPUT SQL: CREATE DOMAIN attachment AS jsonb CHECK (value ?& ARRAY['url', 'mime'] AND (value ->> 'url') ~ E'^(https?)://[^\s/$.?#].[^\s]*$')
📤 DEPARSED SQL: CREATE DOMAIN attachment AS jsonb CHECK (value ?& ARRAY['url', 'mime'] AND (value ->> 'url') ~ '^(https?)://[^\s/$.?#].[^\s]*)
PARSE ERROR: Unexpected token 'u', "unterminat"... is not valid JSON

The detailed logging now appears in test output, proving that async operations are properly awaited and errors are caught.

Impact

This fix enables the test framework to properly catch deparser bugs where invalid SQL is generated. Previously, such bugs would go undetected because the async forEach prevented error propagation.

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

Requested by: Dan Lynch ([email protected])