awsproviderlint: New Check: Prefer %w verb for *awserr.Error in returning errors with context

[breathingdust]

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Description

Go 1.13 introduced a new error formatting verb, %w, which allows the original error to be wrapped and checked by type in consumers, rather than just checking by value.

Previously, it was not (easily) possible to have an AWS Go SDK helper function return a contextual message along the original error, e.g. this would not work

func doSomethingCool(conn *ec2.EC2) error {
  input := &ec2.DescribeSecurityGroupsInput{}
  _, err := conn.DescribeSecurityGroups(input)
  
  if err != nil {
    return fmt.Errorf("error describing EC2 Security Groups: %s", err)
  }

  return nil
}

// calling reference

err := doSomethingCool(conn)

// this would not work previously and the Go build chain will not raise any issues (error is checked by value)
if isAWSErr(err, "Code", "Message") {
  // error handling
}

Now with the %w verb in the AWS Go SDK calling function and the now updated isAWSErr() helper function, the error checking can work as expected.

Flagged Code

fmt.Errorf("oh no: %s", err)

Passing Code

fmt.Errorf("oh no: %w", err)

References

• https://blog.golang.org/go1.13-errors

[ewbankkit]

We should be able to use the golangci-lint errorlint linter for this.

We may want to wait until after #15090 is complete before tackling this one as CRUD handler functions will then return diag.Diagnostics, not error.

[ewbankkit]

Superseded by #15891.

[github-actions]

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