// 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

					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,
			}

	goversion := fmt.Sprintf("go1.%d", goversion.Version)
	for _, v := range []string{
		goversion,
		goversion + ".0",
		goversion + ".1",
		goversion + ".rc",
	} {
		conf := Config{GoVersion: v}
		pkg := mustTypecheck("package p", &conf, nil)
		if pkg.GoVersion() != conf.GoVersion {
			t.Errorf("got %s; want %s", pkg.GoVersion(), conf.GoVersion)
		}
	}
}

		}
		files = append(files, f)
	}
	tc := &types.Config{
		Importer:  makeTypesImporter(cfg, fset),
		Sizes:     types.SizesFor("gc", build.Default.GOARCH), // TODO(adonovan): use cfg.Compiler
		GoVersion: cfg.GoVersion,
	}
	info := &types.Info{
		Types:      make(map[ast.Expr]types.TypeAndValue),
		Defs:       make(map[*ast.Ident]types.Object),
		Uses:       make(map[*ast.Ident]types.Object),

	//
	// Note that we lightly parse internal/goversion/goversion.go to
	// obtain the base version. We can't just import the package,
	// because cmd/dist is built with a bootstrap GOROOT which could
	// be an entirely different version of Go. We assume
	// that the file contains "const Version = <Integer>".
	goversionSource := readfile(pathf("%s/src/internal/goversion/goversion.go", goroot))