How to annotate errors with additional information in Go?

In Go, you can use the github.com/pkg/errors package to annotate errors with additional information. This package provides functionalities to create and handle annotated errors.

Here's an example of how you can annotate errors with additional information:

Import the errors package:

import (
	"github.com/pkg/errors"
	"fmt"
)

Create an annotated error using the errors.Wrap function. This function takes an original error and a string message as arguments. It returns a new error value that wraps the original error with the provided message:

func readFile() error {
	_, err := someFunction()
	if err != nil {
		return errors.Wrap(err, "failed to read file")
	}
	// ...
}

In this example, if someFunction() returns an error, it will be wrapped with the message "failed to read file".

Retrieve the original error and additional information using the errors.Cause and errors.Error functions:

func main() {
	err := readFile()
	if err != nil {
		fmt.Println(errors.Cause(err))
		fmt.Println(err)
	}
}

The errors.Cause function returns the original error (without any annotations), while the errors.Error function returns the full error message including all annotations.

By using this approach, you can pass the error up the call stack while preserving the original error and providing useful context information to handle and report the error.