cmd: extract cmd/go's cfg.LookPath into separate pathcache package

Lift out the LookPath cached lookup utility function into a separate
"cmd/internal/pathcache" package, so that it can be reused in other
commands in addition to cmd/go. No change in functionality.

Change-Id: Ica7fa627000843360c3e353d40a9a70605fbe033
Reviewed-on: https://go-review.googlesource.com/c/go/+/601479
Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/go/internal/cfg/bench_test.go

@@ -5,6 +5,7 @@
 package cfg
 
 import (
+	"cmd/internal/pathcache"
 	"internal/testenv"
 	"testing"
 )
@@ -13,7 +14,7 @@ func BenchmarkLookPath(b *testing.B) {
 	testenv.MustHaveExecPath(b, "go")
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		_, err := LookPath("go")
+		_, err := pathcache.LookPath("go")
 		if err != nil {
 			b.Fatal(err)
 		}

src/cmd/go/internal/cfg/cfg.go

@@ -21,6 +21,7 @@ import (
 	"sync"
 
 	"cmd/go/internal/fsys"
+	"cmd/internal/pathcache"
 )
 
 // Global build parameters (used during package load)
@@ -162,7 +163,7 @@ func defaultContext() build.Context {
 		if ctxt.CgoEnabled {
 			if os.Getenv("CC") == "" {
 				cc := DefaultCC(ctxt.GOOS, ctxt.GOARCH)
-				if _, err := LookPath(cc); err != nil {
+				if _, err := pathcache.LookPath(cc); err != nil {
 					defaultCgoEnabled = false
 				}
 			}

src/cmd/go/internal/generate/generate.go

@@ -28,6 +28,7 @@ import (
 	"cmd/go/internal/modload"
 	"cmd/go/internal/str"
 	"cmd/go/internal/work"
+	"cmd/internal/pathcache"
 )
 
 var CmdGenerate = &base.Command{
@@ -489,7 +490,7 @@ func (g *Generator) exec(words []string) {
 		// intends to use the same 'go' as 'go generate' itself.
 		// Prefer to resolve the binary from GOROOT/bin, and for consistency
 		// prefer to resolve any other commands there too.
-		gorootBinPath, err := cfg.LookPath(filepath.Join(cfg.GOROOTbin, path))
+		gorootBinPath, err := pathcache.LookPath(filepath.Join(cfg.GOROOTbin, path))
 		if err == nil {
 			path = gorootBinPath
 		}

src/cmd/go/internal/load/pkg.go

@@ -44,6 +44,7 @@ import (
 	"cmd/go/internal/trace"
 	"cmd/go/internal/vcs"
 	"cmd/internal/par"
+	"cmd/internal/pathcache"
 	"cmd/internal/pkgpattern"
 
 	"golang.org/x/mod/modfile"
@@ -2443,7 +2444,7 @@ func (p *Package) setBuildInfo(ctx context.Context, autoVCS bool) {
 			goto omitVCS
 		}
 		if cfg.BuildBuildvcs == "auto" && vcsCmd != nil && vcsCmd.Cmd != "" {
-			if _, err := cfg.LookPath(vcsCmd.Cmd); err != nil {
+			if _, err := pathcache.LookPath(vcsCmd.Cmd); err != nil {
 				// We fould a repository, but the required VCS tool is not present.
 				// "-buildvcs=auto" means that we should silently drop the VCS metadata.
 				goto omitVCS

src/cmd/go/internal/script/cmds.go

@@ -5,7 +5,7 @@
 package script
 
 import (
-	"cmd/go/internal/cfg"
+	"cmd/internal/pathcache"
 	"cmd/internal/robustio"
 	"errors"
 	"fmt"
@@ -825,7 +825,7 @@ func Program(name string, cancel func(*exec.Cmd) error, waitDelay time.Duration)
 		},
 		func(s *State, args ...string) (WaitFunc, error) {
 			lookPathOnce.Do(func() {
-				path, pathErr = cfg.LookPath(name)
+				path, pathErr = pathcache.LookPath(name)
 			})
 			if pathErr != nil {
 				return nil, pathErr

src/cmd/go/internal/script/scripttest/scripttest.go

@@ -7,8 +7,8 @@ package scripttest
 
 import (
 	"bufio"
-	"cmd/go/internal/cfg"
 	"cmd/go/internal/script"
+	"cmd/internal/pathcache"
 	"errors"
 	"io"
 	"strings"
@@ -137,7 +137,7 @@ func CachedExec() script.Cond {
 	return script.CachedCondition(
 		"<suffix> names an executable in the test binary's PATH",
 		func(name string) (bool, error) {
-			_, err := cfg.LookPath(name)
+			_, err := pathcache.LookPath(name)
 			return err == nil, nil
 		})
 }

src/cmd/go/internal/toolchain/select.go

@@ -26,6 +26,7 @@ import (
 	"cmd/go/internal/modload"
 	"cmd/go/internal/run"
 	"cmd/go/internal/work"
+	"cmd/internal/pathcache"
 	"cmd/internal/telemetry/counter"
 
 	"golang.org/x/mod/module"
@@ -308,7 +309,7 @@ func Exec(gotoolchain string) {
 	// Look in PATH for the toolchain before we download one.
 	// This allows custom toolchains as well as reuse of toolchains
 	// already installed using go install golang.org/dl/go1.2.3@latest.
-	if exe, err := cfg.LookPath(gotoolchain); err == nil {
+	if exe, err := pathcache.LookPath(gotoolchain); err == nil {
 		execGoToolchain(gotoolchain, "", exe)
 	}
 

src/cmd/go/internal/vcs/vcs.go

@@ -27,6 +27,7 @@ import (
 	"cmd/go/internal/search"
 	"cmd/go/internal/str"
 	"cmd/go/internal/web"
+	"cmd/internal/pathcache"
 
 	"golang.org/x/mod/module"
 )
@@ -678,7 +679,7 @@ func (v *Cmd) run1(dir string, cmdline string, keyval []string, verbose bool) ([
 		args = args[2:]
 	}
 
-	_, err := cfg.LookPath(v.Cmd)
+	_, err := pathcache.LookPath(v.Cmd)
 	if err != nil {
 		fmt.Fprintf(os.Stderr,
 			"go: missing %s command. See https://golang.org/s/gogetcmd\n",

src/cmd/go/internal/work/build.go

@@ -23,6 +23,7 @@ import (
 	"cmd/go/internal/modload"
 	"cmd/go/internal/search"
 	"cmd/go/internal/trace"
+	"cmd/internal/pathcache"
 )
 
 var CmdBuild = &base.Command{
@@ -901,7 +902,7 @@ func FindExecCmd() []string {
 	if cfg.Goos == runtime.GOOS && cfg.Goarch == runtime.GOARCH {
 		return ExecCmd
 	}
-	path, err := cfg.LookPath(fmt.Sprintf("go_%s_%s_exec", cfg.Goos, cfg.Goarch))
+	path, err := pathcache.LookPath(fmt.Sprintf("go_%s_%s_exec", cfg.Goos, cfg.Goarch))
 	if err == nil {
 		ExecCmd = []string{path}
 	}

src/cmd/go/internal/work/buildid.go

@@ -18,6 +18,7 @@ import (
 	"cmd/go/internal/fsys"
 	"cmd/go/internal/str"
 	"cmd/internal/buildid"
+	"cmd/internal/pathcache"
 	"cmd/internal/quoted"
 	"cmd/internal/telemetry/counter"
 )
@@ -292,7 +293,7 @@ func (b *Builder) gccToolID(name, language string) (id, exe string, err error) {
 		}
 		exe = fields[0]
 		if !strings.ContainsAny(exe, `/\`) {
-			if lp, err := cfg.LookPath(exe); err == nil {
+			if lp, err := pathcache.LookPath(exe); err == nil {
 				exe = lp
 			}
 		}

src/cmd/go/internal/work/exec.go

@@ -9,6 +9,7 @@ package work
 import (
 	"bytes"
 	"cmd/internal/cov/covcmd"
+	"cmd/internal/pathcache"
 	"context"
 	"crypto/sha256"
 	"encoding/json"
@@ -2576,7 +2577,7 @@ func (b *Builder) gccCompilerID(compiler string) (id cache.ActionID, ok bool) {
 	//
 	// Otherwise, we compute a new validation description
 	// and compiler id (below).
-	exe, err := cfg.LookPath(compiler)
+	exe, err := pathcache.LookPath(compiler)
 	if err != nil {
 		return cache.ActionID{}, false
 	}

src/cmd/go/internal/work/gccgo.go

@@ -18,6 +18,7 @@ import (
 	"cmd/go/internal/fsys"
 	"cmd/go/internal/load"
 	"cmd/go/internal/str"
+	"cmd/internal/pathcache"
 	"cmd/internal/pkgpath"
 )
 
@@ -33,7 +34,7 @@ func init() {
 	if GccgoName == "" {
 		GccgoName = "gccgo"
 	}
-	GccgoBin, gccgoErr = cfg.LookPath(GccgoName)
+	GccgoBin, gccgoErr = pathcache.LookPath(GccgoName)
 }
 
 func (gccgoToolchain) compiler() string {

src/cmd/go/internal/work/shell.go

@@ -12,6 +12,7 @@ import (
 	"cmd/go/internal/load"
 	"cmd/go/internal/str"
 	"cmd/internal/par"
+	"cmd/internal/pathcache"
 	"errors"
 	"fmt"
 	"internal/lazyregexp"
@@ -606,7 +607,7 @@ func (sh *Shell) runOut(dir string, env []string, cmdargs ...any) ([]byte, error
 	}
 
 	var buf bytes.Buffer
-	path, err := cfg.LookPath(cmdline[0])
+	path, err := pathcache.LookPath(cmdline[0])
 	if err != nil {
 		return nil, err
 	}

src/cmd/internal/pathcache/lookpath.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package cfg
+package pathcache
 
 import (
 	"cmd/internal/par"