x/tools/imports: Process does not remove all unused imports sharing a package name

[Deiz]

What version of Go are you using (go version)?

$ go version
go version go1.16 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

See https://play.golang.org/p/yv78HSm0AX6 for a full example, and https://play.golang.org/p/GmUF-tayOgI for an interactive example (hit "Format" with imports enabled).

What did you expect to see?

package main

import (
	"errors"

	"github.com/pkg/errors"
	"github.com/juju/errors"
)

func main() {
}

This file has three imported errors packages, none of them are referenced outside of the import block, so they should all be removed, resulting in this output:

package main

func main() {
}

What did you see instead?

Only one errors package is removed per iteration - seemingly always the last one to appear. Because we have three imported packages, we need to run imports.Process three times to prune all the unused imports.

Iteration 1:

package main

import (
    "errors"

    "github.com/pkg/errors"
)

func main() {
}

Iteration 2:

package main

import (
    "errors"
)

func main() {
}

Iteration 3:

package main

func main() {
}

[gopherbot]

Change https://golang.org/cl/307449 mentions this issue: internal/imports: remove duplicate unused imports

[stevenh]

I just hit this issue and came up with the same fix independently.

@heschi I know there's an open question on what happens for used identifiers but would be great if we could fix this case and look at that one later as currently goimports and all tools which use the x/tools/imports package is unstable due to this issue.