var buildtagFix = fix{
	name: "buildtag",
	date: "2021-08-25",
	f:    buildtag,
	desc: `Remove +build comments from modules using Go 1.18 or later`,
}

func buildtag(f *ast.File) bool {
	if version.Compare(*goVersion, buildtagGoVersionCutoff) < 0 {
		return false
	}

	// File is already gofmt-ed, so we know that if there are +build lines,
	// they are in a comment group that starts with a //go:build line followed

	// since at that time the go directive wasn't clearly
	// specified as a toolchain requirement.
	//
	// TODO(adonovan): after go1.21, call GoVersion directly.
	pkgVersion := any(pass.Pkg).(interface{ GoVersion() string }).GoVersion()
	if !versions.AtLeast(pkgVersion, "go1.21") {
		return nil, nil
	}

	// disallowedSymbols returns the set of standard library symbols

	// determine Go version for each file
	for _, file := range check.files {
		// use unaltered Config.GoVersion by default
		// (This version string may contain dot-release numbers as in go1.20.1,
		// unlike file versions which are Go language versions only, if valid.)
		v := check.conf.GoVersion

		fileVersion := asGoVersion(file.GoVersion)
		if fileVersion.isValid() {
			// use the file version, if applicable

		compatVersion := ld.TidyCompatibleVersion
		goVersion := ld.requirements.GoVersion()
		if compatVersion == "" {
			if gover.Compare(goVersion, gover.GoStrictVersion) < 0 {
				compatVersion = gover.Prev(goVersion)
			} else {
				// Starting at GoStrictVersion, we no longer maintain compatibility with
				// versions older than what is listed in the go.mod file.
				compatVersion = goVersion
			}
		}

env GOWORK=$GOPATH/src/unformatted
go work edit -print -fmt
cmp stdout $GOPATH/src/formatted

-- m/go.mod --
module m

go 1.18
-- go.work.want_initial --
go $goversion

use ./m
-- go.work.want_use_n --
go $goversion

use (
	./m
	./n
)
-- go.work.want_go_118 --
go 1.18

use (
	./m
	./n
)
-- go.work.want_dropuse_m --
go 1.18

use ./n

// version of the form "v1.2.3". Go versions may also include spaces and
// special characters.
func ProgramInfo(info *debug.BuildInfo) (goVers, progPath, progVers string) {
	goVers = info.GoVersion
	if strings.Contains(goVers, "devel") || strings.Contains(goVers, "-") {
		goVers = "devel"
	}

	progPath = info.Path
	if progPath == "" {
		progPath = strings.TrimSuffix(filepath.Base(os.Args[0]), ".exe")
	}

	// determine Go version for each file
	for _, file := range check.files {
		// use unaltered Config.GoVersion by default
		// (This version string may contain dot-release numbers as in go1.20.1,
		// unlike file versions which are Go language versions only, if valid.)
		v := check.conf.GoVersion

		fileVersion := asGoVersion(file.GoVersion)
		if fileVersion.isValid() {
			// use the file version, if applicable

					vars = append(vars, obj)
				}
			}
		}
		var body *ast.BlockStmt
		switch n := n.(type) {
		case *ast.File:
			// Only traverse the file if its goversion is strictly before go1.22.
			goversion := versions.FileVersion(pass.TypesInfo, n)
			return versions.Before(goversion, versions.Go1_22)
		case *ast.RangeStmt:
			body = n.Body
			addVar(n.Key)
			addVar(n.Value)
		case *ast.ForStmt:
			body = n.Body

					const prefix = "-lang="
					if strings.HasPrefix(arg, prefix) {
						goVersion = arg[len(prefix):]
					}
				}
			}
		}

		// parse and type-check file
		if testing.Verbose() {
			fmt.Println("\t", filename)
		}
		file, err := syntax.ParseFile(filename, nil, nil, 0)
		if err == nil {
			conf := Config{
				GoVersion: goVersion,
				Importer:  stdLibImporter,
			}

! stderr .+

# go env -w rejects unknown or bad variables
! go env -w GOGC=off
stderr 'unknown go command variable GOGC'
! go env -w GOEXE=.bat
stderr 'GOEXE cannot be modified'
! go env -w GOVERSION=customversion
stderr 'GOVERSION cannot be modified'
! go env -w GOENV=/env
stderr 'GOENV can only be set using the OS environment'
! go env -w GODEBUG=gctrace=1
stderr 'GODEBUG can only be set using the OS environment'