Goimports error message insufficient with `local-prefixes`

[ian-howell]

The error message for goimports is currently insufficient when run with a local-prefixes. Suppose we have the following:

main.go:

package main

import (
        "fmt"

        "github.com/ian-howell/foo/pkg"
        "github.com/spf13/cobra"
)

func main() {
        fmt.Println(pkg.Foo())
        _ = cobra.Command{}
}

.golangci.yaml:

linters-settings:
  goimports:
    local-prefixes: github.com/ian-howell/foo
linters:
  disable-all: true
  enable:
    - goimports

Running golangci-lint run -c .golangci.yaml produces the following output:

main.go:6: File is not `goimports`-ed (goimports)
        "github.com/ian-howell/foo/pkg"

This message is confusing, because running goimports on the file doesn't seem to find any issues:

$ diff <(goimports main.go) main.go
$ # no output

Of course, running goimports with the -local flag does provide output, but golangci-lint does not indicate that the flag is needed:

$ diff <(goimports -local github.com/ian-howell/foo main.go) main.go
6,7d5
<       "github.com/spf13/cobra"
<
8a7
>       "github.com/spf13/cobra"