x/tools/go/analysis/passes/modernize: mapsloop should use `maps.Clone` when it can prove the operand is non-nil

gopls version

binary compiled by latest code

go env

AR='ar'
CC='cc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='c++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN='/Users/mac/go/bin'
GOCACHE='/Users/mac/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/mac/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/tq/m955dwkd1519phkp2hwpv9_80000gn/T/go-build2400307511=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/Users/mac/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/mac/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/mac/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.24.3'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

For the following code:

package main

import (
	"fmt"
	"maps"
)

var fruitProperties = map[string][]string{
	"apple":  {"red", "sweet", "crispy"},
	"banana": {"yellow", "soft", "tropical"},
	"orange": {"orange", "citrus", "juicy"},
	"grape":  {"purple", "small", "sweet"},
}

func GetFruitPropertiesOld() map[string][]string {
	dupProperties := make(map[string][]string)
	for k, v := range fruitProperties {
		dupProperties[k] = v
	}
	return dupProperties
}

func GetFruitPropertiesNew() map[string][]string {
	return maps.Clone(fruitProperties)
}

func main() {
	oldCopy := GetFruitPropertiesOld()
	fmt.Println(oldCopy)

	newCopy := GetFruitPropertiesNew()
	fmt.Println(newCopy)

	newCopy["apple"] = []string{"green", "sour"}

	fmt.Println("original map:", fruitProperties["apple"])
	fmt.Println("new clone map:", newCopy["apple"])
}

What did you see happen?

After being processed by the modernize analyzer, it will be transformed into the following

package main

import (
	"fmt"
	"maps"
)

var fruitProperties = map[string][]string{
	"apple":  {"red", "sweet", "crispy"},
	"banana": {"yellow", "soft", "tropical"},
	"orange": {"orange", "citrus", "juicy"},
	"grape":  {"purple", "small", "sweet"},
}

func GetFruitPropertiesOld() map[string][]string {
	dupProperties := make(map[string][]string)
	maps.Copy(dupProperties, fruitProperties)
	return dupProperties
}

func GetFruitPropertiesNew() map[string][]string {
	return maps.Clone(fruitProperties)
}

func main() {
	oldCopy := GetFruitPropertiesOld()
	fmt.Println(oldCopy)

	newCopy := GetFruitPropertiesNew()
	fmt.Println(newCopy)

	newCopy["apple"] = []string{"green", "sour"}

	fmt.Println("original map:", fruitProperties["apple"])
	fmt.Println("new clone map:", newCopy["apple"])
}

What did you expect to see?

It is better to use maps.Clone than maps.Copy here. Just like GetFruitPropertiesNew

Editor and settings

No response

Logs

No response

Start in x/tools/go/analysis/passes/modernize, focusing on the mapsloop analyzer and its existing tests. Compare the reported maps.Copy transformation with the non-nil operand example, then add coverage showing that eligible loops are transformed to maps.Clone while other cases retain their current behavior.