named

named

Linter named ensures a target function to be called with a named return value.

A typical use case is to prevent the misuse of a error wrapping function such as derrors.Wrap, which does not allow the resulted error to be unwrapped. Function Bad below fails to wrap the error simply because it doesn't use the named return value as an argument.

func Good() (err error) {
  err = DoSomething()
  defer Wrap(&err, "wrapped!!") // ok because a named return value is passed.
  return fmt.Errorf("error from Good: %w", err)
}

func Bad() error {
  err := DoSomething()
  defer Wrap(&err, "wrapped!!") // <- err is not a named return value.
  return fmt.Errorf("error from Bad: %w", err)
}

func Wrap(errp *error, msg string) {
  if *errp == nil {
    return
  }
  *errp = fmt.Errorf("%s: %w", msg, *errp)
}

func DoSomething() error {
  return errors.New("original error")
}

func main() {
  err := Good()
  fmt.Println(err)
  err = Bad()
  fmt.Println(err)
  // Output:
  // wrapped!!: error from Good: original error
  // error from Bad: original error
}

How to use

Build your named binary by writing main.go like below.

package main

import (
  "github.com/qawatake/named"
  "golang.org/x/tools/go/analysis/unitchecker"
)

func main() {
  unitchecker.Main(
    named.NewAnalyzer(
      named.Deferred{
        PkgPath:  "pkg/in/which/target/func/is/defined",
        FuncName: "Wrap",
        ArgPos:   0,
      },
    ),
  )
}

Then, run go vet with your named binary.

go vet -vettool=/path/to/your/named ./...