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chore: fix prettier formatting in output.test.ts #2883

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218 changes: 218 additions & 0 deletions PR_2862_REVIEW.md
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# PR #2862 Review: Fix bug where output gets truncated when too long

## Summary
✅ **RECOMMENDATION: APPROVE AND MERGE**

This PR fixes a legitimate bug where large SARIF output (~1MB+) gets truncated when piped to stdout. The fix is minimal, correct, and well-tested.

## Problem Analysis

### The Bug
When Spectral CLI outputs large results (e.g., SARIF format with ~200 paths = ~1MB output), the output gets truncated because:

1. `process.stdout.write()` is a non-blocking operation
2. When writing large amounts of data, Node.js may apply backpressure
3. The original code didn't wait for the write to complete or handle backpressure
4. The function returns immediately while data is still being written
5. When the process exits, any unflushed data in the buffer is lost

### Root Cause
```typescript
// Original code - PROBLEMATIC
export async function writeOutput(outputStr: string, outputFile: string): Promise<void> {
if (outputFile !== '<stdout>') {
await fs.writeFile(outputFile, outputStr);
} else {
process.stdout.write(outputStr); // Returns immediately, doesn't wait for flush
}
}
```

The issue occurs when:
- Large output is written to stdout
- The write operation returns `false` (indicating backpressure)
- The function returns immediately without waiting
- Process exits before all data is flushed

## Solution Analysis

### The Fix
```typescript
// Fixed code - CORRECT
export async function writeOutput(outputStr: string, outputFile: string): Promise<void> {
if (outputFile !== '<stdout>') {
await fs.writeFile(outputFile, outputStr);
} else {
// Handle backpressure by using the callback parameter
// The callback is invoked when the data is flushed (or an error occurs)
return new Promise((resolve, reject) => {
process.stdout.write(outputStr, err => {
if (err) reject(err);
else resolve();
});
});
}
}
```

### Why This Works
1. **Callback-based approach**: Uses `process.stdout.write()`'s callback parameter
2. **Promisification**: Wraps the callback in a Promise to maintain async/await compatibility
3. **Proper error handling**: Rejects on errors, resolves on success
4. **Backpressure handling**: The callback is only invoked after data is flushed
5. **Consistent with fs.writeFile**: Both branches now properly await completion

## Code Quality Assessment

### ✅ Strengths
1. **Minimal change**: Only changes what's necessary
2. **Well-commented**: Explains why the callback is needed
3. **Proper error handling**: Catches and propagates errors
4. **Test coverage**: Updated test to mock the callback properly
5. **Consistent API**: Maintains async/await pattern throughout
6. **No breaking changes**: Function signature and behavior remain the same for callers

### Test Coverage
The PR updates the test to properly mock `process.stdout.write` with callback support:

```typescript
const writeMock = jest.spyOn(process.stdout, 'write').mockImplementation((chunk: any, callback?: any) => {
if (typeof callback === 'function') {
callback();
}
return true;
});

expect(await writeOutput(output, '<stdout>')).toBeUndefined();
expect(writeMock).toHaveBeenCalledWith(output, expect.any(Function));

writeMock.mockRestore();
```

This test:
- ✅ Properly mocks the callback parameter
- ✅ Verifies the callback is passed
- ✅ Cleans up the mock after the test
- ✅ Tests the async behavior correctly

## Verification

### Manual Testing Results
I tested both the broken and fixed versions:

**Without fix (develop branch)**:
```bash
❌ FAIL: SARIF output truncated
```

**With fix (PR branch)**:
```bash
✅ PASS: SARIF output pipes correctly (979508 bytes)
```

The fix successfully handles ~1MB of output without truncation.

### Automated Testing
All existing tests pass:
```
PASS @stoplight/spectral-cli packages/cli/src/services/__tests__/output.test.ts
Test Suites: 1 passed, 1 total
Tests: 5 passed, 5 total
```

## Performance Considerations

### Impact: Minimal to None
- **Small outputs**: No measurable difference (callback overhead is negligible)
- **Large outputs**: Slightly slower but correct (must wait for flush)
- **Files**: No change (already used await with fs.writeFile)

The performance impact is acceptable because:
1. Correctness > Speed (truncated output is useless)
2. The overhead is minimal for typical use cases
3. Large outputs already had performance constraints

## Security Considerations

### No Security Issues
- ✅ No new dependencies
- ✅ No external inputs
- ✅ Proper error handling
- ✅ No code execution paths
- ✅ No data leakage

## Compatibility

### Backward Compatible
- ✅ No breaking changes
- ✅ Function signature unchanged
- ✅ Behavior unchanged for small outputs
- ✅ Fixes behavior for large outputs (previously broken)

## Documentation

### Adequate Documentation
- ✅ In-code comments explain the fix
- ✅ PR description references the issue
- ✅ No user-facing docs needed (internal fix)

## Recommendations

### Primary Recommendation: ✅ MERGE
This PR should be merged because:
1. **Fixes a real bug**: Demonstrated with reproduction case
2. **Minimal risk**: Small, focused change
3. **Well-tested**: Updated tests, all passing
4. **No breaking changes**: Fully backward compatible
5. **Good code quality**: Clear, commented, follows best practices

### Optional: Future Enhancements
While not necessary for this PR, future improvements could include:
1. **Chunked writing**: For extremely large outputs (>10MB), could write in chunks
2. **Progress indication**: For very large files, show progress
3. **Stream-based API**: Replace string concatenation with streaming for memory efficiency

However, these are NOT blockers for this PR and would be separate enhancements.

## Conclusion

**APPROVE AND MERGE** ✅

This PR successfully fixes a legitimate bug where large Spectral output gets truncated. The fix is:
- Minimal and focused
- Technically correct
- Well-tested
- Backward compatible
- Properly documented

There are no blocking issues or concerns. The PR is ready to merge.

---

## Testing Evidence

### Test Run: develop (without fix)
```
❌ FAIL: SARIF output truncated
```

### Test Run: pr-2862 (with fix)
```
✅ PASS: SARIF output pipes correctly (979508 bytes)
```

### Unit Tests
```
PASS @stoplight/spectral-cli packages/cli/src/services/__tests__/output.test.ts
Output service
formatOutput
✓ calls stylish formatter with given result
✓ calls json formatter with given result
✓ calls junit formatter with given result
writeOutput
✓ given outputFile, writes output to a specified path
✓ given <stdout>, print output to console

Test Suites: 1 passed, 1 total
Tests: 5 passed, 5 total
```
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