1 files changed, 105 insertions, 0 deletions
diff --git a/src/cmd/internal/script/scripttest/setup.go b/src/cmd/internal/script/scripttest/setup.go
new file mode 100644
index 0000000000..d430367c12
--- /dev/null
+++ b/src/cmd/internal/script/scripttest/setup.go
@@ -0,0 +1,105 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package scripttest adapts the script engine for use in tests.
+package scripttest
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+// SetupTestGoRoot sets up a temporary GOROOT for use with script test
+// execution. It copies the existing goroot bin and pkg dirs using
+// symlinks (if possible) or raw copying. Return value is the path to
+// the newly created testgoroot dir.
+func SetupTestGoRoot(t *testing.T, tmpdir string, goroot string) string {
+	mustMkdir := func(path string) {
+		if err := os.MkdirAll(path, 0777); err != nil {
+			t.Fatalf("SetupTestGoRoot mkdir %s failed: %v", path, err)
+		}
+	}
+
+	replicateDir := func(srcdir, dstdir string) {
+		files, err := os.ReadDir(srcdir)
+		if err != nil {
+			t.Fatalf("inspecting %s: %v", srcdir, err)
+		}
+		for _, file := range files {
+			fn := file.Name()
+			linkOrCopy(t, filepath.Join(srcdir, fn), filepath.Join(dstdir, fn))
+		}
+	}
+
+	// Create various dirs in testgoroot.
+	toolsub := filepath.Join("tool", runtime.GOOS+"_"+runtime.GOARCH)
+	tomake := []string{
+		"bin",
+		"src",
+		"pkg",
+		filepath.Join("pkg", "include"),
+		filepath.Join("pkg", toolsub),
+	}
+	made := []string{}
+	tgr := filepath.Join(tmpdir, "testgoroot")
+	mustMkdir(tgr)
+	for _, targ := range tomake {
+		path := filepath.Join(tgr, targ)
+		mustMkdir(path)
+		made = append(made, path)
+	}
+
+	// Replicate selected portions of the content.
+	replicateDir(filepath.Join(goroot, "bin"), made[0])
+	replicateDir(filepath.Join(goroot, "src"), made[1])
+	replicateDir(filepath.Join(goroot, "pkg", "include"), made[3])
+	replicateDir(filepath.Join(goroot, "pkg", toolsub), made[4])
+
+	return tgr
+}
+
+// ReplaceGoToolInTestGoRoot replaces the go tool binary toolname with
+// an alternate executable newtoolpath within a test GOROOT directory
+// previously created by SetupTestGoRoot.
+func ReplaceGoToolInTestGoRoot(t *testing.T, testgoroot, toolname, newtoolpath string) {
+	toolsub := filepath.Join("pkg", "tool", runtime.GOOS+"_"+runtime.GOARCH)
+	exename := toolname
+	if runtime.GOOS == "windows" {
+		exename += ".exe"
+	}
+	toolpath := filepath.Join(testgoroot, toolsub, exename)
+	if err := os.Remove(toolpath); err != nil {
+		t.Fatalf("removing %s: %v", toolpath, err)
+	}
+	linkOrCopy(t, newtoolpath, toolpath)
+}
+
+// linkOrCopy creates a link to src at dst, or if the symlink fails
+// (platform doesn't support) then copies src to dst.
+func linkOrCopy(t *testing.T, src, dst string) {
+	err := os.Symlink(src, dst)
+	if err == nil {
+		return
+	}
+	srcf, err := os.Open(src)
+	if err != nil {
+		t.Fatalf("copying %s to %s: %v", src, dst, err)
+	}
+	defer srcf.Close()
+	perm := os.O_WRONLY | os.O_CREATE | os.O_EXCL
+	dstf, err := os.OpenFile(dst, perm, 0o777)
+	if err != nil {
+		t.Fatalf("copying %s to %s: %v", src, dst, err)
+	}
+	_, err = io.Copy(dstf, srcf)
+	if closeErr := dstf.Close(); err == nil {
+		err = closeErr
+	}
+	if err != nil {
+		t.Fatalf("copying %s to %s: %v", src, dst, err)
+	}
+}