x/tools/go/analysis/internal/checker: remove imports that are unused after a batch of fixes are applied

[cuishuang]

Go version

go 1.24.2

Output of go env in your module/workspace:

AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='0'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE='auto'
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/xxx/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/xxx/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/9t/839s3jmj73bcgyp5x_xh3gw00000gn/T/go-build2973783802=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/Users/xxxx/20250428/tools/gopls/go.mod'
GOMODCACHE='/Users/xxx/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/xxx/go'
GOPRIVATE=''
GOPROXY='https://goproxy.cn,direct'
GOROOT='/usr/local/go'
GOSUMDB='off'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/xxx/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.24.2'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

package main

import (
	"fmt"
	"sort"
)

func main() {

	a := []uint32{3, 1, 4, 1, 5, 9}
	Uint32Sort(a)

	fmt.Println(a)

}

func Uint32Sort(arr []uint32) {
	sort.Slice(arr, func(i, j int) bool { return arr[i] < arr[j] })
}

Output:

[1 1 3 4 5 9]

What did you see happen?

After executing modernize -fix -test ./..., it will become.

package main

import (
	"fmt"
	"slices"
	"sort"
)

func main() {

	a := []uint32{3, 1, 4, 1, 5, 9}
	Uint32Sort(a)

	fmt.Println(a)

}

func Uint32Sort(arr []uint32) {
	slices.Sort(arr)
}

Output:

# command-line-arguments
./main.go:6:2: "sort" imported and not used

What did you expect to see?

The sort package should be handled correctly; if there are other places in this file using methods from the sort package, they should be retained. Otherwise, they should be removed.

[gopherbot]

Change https://go.dev/cl/669515 mentions this issue: gopls/internal/analysis/modernize: fix the package import logic for the sortslice analyzer

[adonovan]

This is not a problem of the modernize analyzer, but a general problem across all our refactoring tools that may remove a reference to an imported package. If a fix removes the last reference, the import needs to be deleted. However, the fix may be one of several, and it is only when all of them are composed that the last reference disappears, so the responsibility to remove the import is a property of the collection of fixes. That means it can really only be addressed by the analysis driver. The correct fix is for the driver to (in effect) run goimports when formatting the code after all fixes have been applied.

[adonovan]

Closing as dup of #72035

[cuishuang]

This is not a problem of the modernize analyzer, but a general problem across all our refactoring tools that may remove a reference to an imported package. If a fix removes the last reference, the import needs to be deleted. However, the fix may be one of several, and it is only when all of them are composed that the last reference disappears, so the responsibility to remove the import is a property of the collection of fixes. That means it can really only be addressed by the analysis driver. The correct fix is for the driver to (in effect) run goimports when formatting the code after all fixes have been applied.

Thanks for your guidance. It should indeed be handled this way.

I tried running modernize -fix -test ./... on this code:

package main

import "fmt"

func main() {
	sourceMap := map[string]int{
		"apple":  1,
		"banana": 2,
		"cherry": 3,
	}

	destMap := map[string]int{
		"banana": 10,
		"date":   20,
	}

	for key, value := range sourceMap {
		destMap[key] = value
	}

	fmt.Println(destMap)
}

After executing modernize -fix -test ./..., it changes to:

package main

import "maps"

import "fmt"

func main() {
	sourceMap := map[string]int{
		"apple":  1,
		"banana": 2,
		"cherry": 3,
	}

	destMap := map[string]int{
		"banana": 10,
		"date":   20,
	}

	maps.Copy(destMap, sourceMap)

	fmt.Println(destMap)
}

It requires explicitly running goimports -w *.go to change it to the expected:

import (
	"fmt"
	"maps"
)

This work should indeed not be done by a single analyzer.