Swallowed errors: except: pass, an empty catch, catch (Exception e) { return null; }, Go's if err != nil { return nil }

Errors and checks hidden: one of the ways AI coding agents bloat software, from lessloc's pattern catalog. lessloc catches it as swallowed-error.

What makes swallowed errors a bad practice?

The standards that call it a bad practice: CWE-390 Detection of Error Condition Without Action; CWE-1069 Empty Exception Block; CWE-396.

What does lessloc do about swallowed errors?

lessloc catches it as swallowed-error.

• swallowed-error (tier 1): An error caught and dropped, such as except Exception: pass or an empty catch. The agent hears about it right after the write.

Examples

Caught as swallowed-error:

export function read(f) {
  try {
    return f();
  } catch (e) {
    // ignore
  }
}

Written well:

export function read(f) {
  try {
    return f();
  } catch (e) {
    if (e.code !== "ENOENT") throw e;
  }
}

Caught as swallowed-error:

package ad

func Load(get func() error) error {
	if err := get(); err != nil {
		return nil
	}
	return nil
}

func Save(put func() error) error {
	err := put()
	if err != nil {
		return nil
	}
	return nil
}

Written well:

package ad

func Save(put func() error) error {
	err := put()
	if err != nil {
		return err
	}
	return nil
}

Related patterns

The other patterns in Errors and checks hidden:

• Silenced checks: lessloc catches it as suppression.
• Checks, fallbacks and catches for cases that cannot happen: defensive catches a null check of a value just created, a type re-checked inside private code and ?. on a fresh object.
• Removing validation or error handling to shrink code: lessloc catches it as removed-safeguard.