golint-sl

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nopanic

About 367 words

Ensures library code returns errors instead of panicking.

Category

Safety

What It Checks

This analyzer detects calls that end the program in library code, where an error should be returned instead:

  • panic() calls
  • Fatal and Panic log calls: the log and logrus package functions (log.Fatal, logrus.Panicf, ...) and the Fatal* and Panic* methods of the log, logrus and zap loggers, however the logger is reached: a variable, a struct field (s.logger.Fatal), zap.L().Fatal or logrus.WithError(err).Fatal

Main packages, _test.go files, init functions and TestMain are not checked. Calling a Must* helper such as regexp.MustCompile is not reported; a Must* function of your own that calls panic is reported like any other panic. The Fatal*, Panic* and DPanic* methods of a logger that wraps another, such as otelzap's, are not reported either: terminating is what they are for.

Why It Matters

Libraries that panic crash their callers:

// Caller's code crashes unexpectedly
result := yourlib.Process(data)  // panic!

Libraries should return errors, letting callers decide how to handle them:

result, err := yourlib.Process(data)
if err != nil {
    // Caller handles it appropriately
}

Examples

Bad: Library Panics

// mylib/processor.go
func Process(data []byte) Result {
    if len(data) == 0 {
        panic("data cannot be empty")  // Crashes caller!
    }
    // ...
}

Good: Library Returns Error

// mylib/processor.go
func Process(data []byte) (Result, error) {
    if len(data) == 0 {
        return Result{}, errors.New("data cannot be empty")
    }
    // ...
}

Allowed: Panic in main/init

// cmd/myapp/main.go
func main() {
    if err := run(); err != nil {
        panic(err)  // OK in main
    }
}

func init() {
    if os.Getenv("REQUIRED") == "" {
        panic("REQUIRED env var not set")  // OK in init
    }
}

Intentional: Unreachable Code

A panic that marks a programmer error is still reported. Suppress it where it's intentional:

func processType(t Type) string {
    switch t {
    case TypeA:
        return "a"
    case TypeB:
        return "b"
    default:
        panic("unreachable") //nolint:nopanic // indicates a bug in the caller
    }
}

Configuration

# .golint-sl.yaml
analyzers:
  nopanic: true  # enabled by default

When to Disable

  • Application code (not a library)
  • Internal packages not meant for external use
analyzers:
  nopanic: false