Emperror: Errors

Drop-in replacement for the standard library errors package and github.com/pkg/errors.

This is a single, lightweight library merging the features of standard library errors package and github.com/pkg/errors. It also backports a few features (like Go 1.13 error handling related features).

Standard library features:

• New creates an error with stack trace
• Unwrap supports both Go 1.13 wrapper (interface { Unwrap() error }) and pkg/errors causer (interface { Cause() error }) interface
• Backported Is and As functions

github.com/pkg/errors features:

• New, Errorf, WithMessage, WithMessagef, WithStack, Wrap, Wrapf functions behave the same way as in the original library
• Cause supports both Go 1.13 wrapper (interface { Unwrap() error }) and pkg/errors causer (interface { Cause() error }) interface

Additional features:

• NewPlain creates a new error without any attached context, like stack trace
• Sentinel is a shorthand type for creating constant error
• WithStackDepth allows attaching stack trace with a custom caller depth
• WithStackDepthIf, WithStackIf, WrapIf, WrapIff only annotate errors with a stack trace if there isn't one already in the error chain
• Multi error aggregating multiple errors into a single value
• NewWithDetails, WithDetails and Wrap*WithDetails functions to add key-value pairs to an error
• Match errors using the match package

Installation

go get emperror.dev/errors

Usage

package main

import "emperror.dev/errors"

// ErrSomethingWentWrong is a sentinel error which can be useful within a single API layer.
const ErrSomethingWentWrong = errors.Sentinel("something went wrong")

// ErrMyError is an error that can be returned from a public API.
type ErrMyError struct {
	Msg string
}

func (e ErrMyError) Error() string {
	return e.Msg
}

func foo() error {
	// Attach stack trace to the sentinel error.
	return errors.WithStack(ErrSomethingWentWrong)
}

func bar() error {
	return errors.Wrap(ErrMyError{"something went wrong"}, "error")
}

func main() {
	if err := foo(); err != nil {
		if errors.Cause(err) == ErrSomethingWentWrong { // or errors.Is(ErrSomethingWentWrong)
			// handle error
		}
	}

	if err := bar(); err != nil {
		if errors.As(err, &ErrMyError{}) {
			// handle error
		}
	}
}

Match errors:

package main

import (
    "emperror.dev/errors"
    "emperror.dev/errors/match"
)

// ErrSomethingWentWrong is a sentinel error which can be useful within a single API layer.
const ErrSomethingWentWrong = errors.Sentinel("something went wrong")

type clientError interface{
    ClientError() bool
}

func foo() error {
	// Attach stack trace to the sentinel error.
	return errors.WithStack(ErrSomethingWentWrong)
}

func main() {
    var ce clientError
    matcher := match.Any{match.As(&ce), match.Is(ErrSomethingWentWrong)}

	if err := foo(); err != nil {
		if matcher.MatchError(err) {
			// you can use matchers to write complex conditions for handling (or not) an error
            // used in emperror
		}
	}
}

Development

Contributions are welcome! :)

1. Clone the repository
2. Make changes on a new branch
3. Run the test suite:

   ./pleasew build
   ./pleasew test
   ./pleasew gotest
   ./pleasew lint

4. Commit, push and open a PR

License

The MIT License (MIT). Please see License File for more information.

Certain parts of this library are inspired by (or entirely copied from) various third party libraries. Their licenses can be found in the Third Party License File.