[linter-miner] Add unchecked-deferred-close linter - #67481

Summary

This PR implements a new Go static analyzer linter that reports defer close() calls that ignore error return values, which can silently hide resource cleanup failures.

Problem

Go's io.Closer interface (and many similar types) define Close() to return an error that callers should handle. However, it's common to see code that defers Close() without checking errors:

f, err := os.Open(filename)
if err != nil {
  return err
}
defer f.Close()  // ❌ Error is silently ignored!

This can mask real issues during resource cleanup, such as:

• Buffered writes not being flushed
• Network connection state issues
• File system errors

Evidence

The code-pattern-scanner agent found this pattern in the actual gh-aw codebase:

• pkg/cli/outcome_eval_jsonl.go:14 - defer f.Close()
• pkg/cli/firewall_log.go:18 - defer file.Close()
• pkg/cli/update_workflows.go:25 - defer resp.Body.Close()
• pkg/cli/bootstrap_profile_github_app.go:42 - defer listener.Close()
• And 6+ additional files with the same pattern

Solution

The new unchecked_deferredclose linter:

1. Detects all defer obj.Close() statements
2. Checks if the Close() method returns an error
3. Reports diagnostic for methods with error returns
4. Respects (nolint/redacted):unchecked_deferredclose directives
5. Skips generated files and types with non-error Close()

Recommended Fix

Replace simple defer with explicit error handling:

defer func() {
  if err := f.Close(); err != nil {
    // log or return error as appropriate
    fmt.Fprintf(os.Stderr, "close error: %v\n", err)
  }
}()

Testing

• Unit tests with good/bad fixtures ✅
• Compiles with existing linter infrastructure ✅
• Registered in pkg/linters/registry.go ✅
• Verified on real codebase patterns ✅

Implementation Details

• Location: pkg/linters/unchecked-deferred-close/
• Analyzer Name: unchecked_deferredclose
• Type Safety: Uses go/types to verify Close() signature
• Pattern Coverage: All Close() method calls (pointers, interfaces, named types)

Files Changed

• pkg/linters/unchecked-deferred-close/unchecked_deferredclose.go - Main linter implementation
• pkg/linters/unchecked-deferred-close/unchecked_deferredclose_test.go - Test suite
• pkg/linters/unchecked-deferred-close/testdata/src/basic/ - Test fixtures
• pkg/linters/registry.go - Register new analyzer

Generated by Linter Miner · copilot · mai10 · 110.1 AIC · ⊞ 6.6K · ◷

• expires on Oct 17, 2026, 9:39 AM UTC-08:00