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Wrapped error is always nil

ID: go/unexpected-nil-value
Kind: problem
Security severity: 
Severity: warning
Precision: high
Tags:
   - reliability
   - correctness
   - logic
Query suites:
   - go-security-and-quality.qls

Click to see the query in the CodeQL repository

The pkg.errors package provides the errors.Wrap function for annotating an error with a stack trace. When passed nil, this function returns nil. When the first parameter to errors.Wrap is always nil, the function call has no effect and likely indicates a programming mistake. A common example of this is when an errors.Wrap(err, "message") call is copied from an earlier error-handling block in the same function and used in a subsequent error-handling block that does not check err in its guard. In this case the return of a nil value to the caller indicates by convention that the operation succeeded, and so the failure is masked.

Recommendation

Usually an err value is being referenced outside its intended scope. The problem can be fixed by removing that reference, for example by changing a call of the form errors.Wrap(err, "message") to errors.New("message").

Example

The example below shows an example where the err value returned from the call to f1 is reused in a later call, when it is known to be nil:

package main

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

func f1(input string) error {
	if input == "1" {
		return errors.Errorf("error in f1")
	}
	return nil
}

func f2(input string) (bool, error) {
	if input == "2" {
		return false, errors.Errorf("error in f2")
	}
	return true, nil
}

func test1(input string) error {
	err := f1(input)
	if err != nil {
		return errors.Wrap(err, "input is the first non-negative integer")
	}
	if ok2, _ := f2(input); !ok2 {
		return errors.Wrap(err, "input is the second non-negative integer")
	}
	return nil
}

One way of fixing this is to create a new error value with errors.New:

package main

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

func f1(input string) error {
	if input == "1" {
		return errors.Errorf("error in f1")
	}
	return nil
}

func f2(input string) (bool, error) {
	if input == "2" {
		return false, errors.Errorf("error in f2")
	}
	return true, nil
}

func test1(input string) error {
	err := f1(input)
	if err != nil {
		return errors.Wrap(err, "input is the first non-negative integer")
	}
	if ok2, _ := f2(input); !ok2 {
		return errors.New("input is the second non-negative integer")
	}
	return nil
}

References

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