Error Wrapping Uses Wrong Format Verb

Why This Happens

fmt.Errorf with %v converts the error to a string, losing the error chain. Using %w wraps the original error so that errors.Is() and errors.As() can still find it. This is essential for proper error handling in Go 1.13+.

The Problem

func readConfig(path string) error {
    data, err := os.ReadFile(path)
    if err != nil {
        return fmt.Errorf("failed to read config: %v", err) // loses error chain
    }
    _ = data
    return nil
}

The Fix

func readConfig(path string) error {
    data, err := os.ReadFile(path)
    if err != nil {
        return fmt.Errorf("failed to read config: %w", err) // preserves error chain
    }
    _ = data
    return nil
}

Step-by-Step Fix

1. 1

   Identify %v with errors

   Find fmt.Errorf calls that format errors with %v or %s instead of %w.

2. 2

   Replace with %w

   Change the format verb to %w to wrap the error properly.

3. 3

   Verify unwrapping

   Test that errors.Is() and errors.As() work correctly with the wrapped error.