cmd/go/internal/vcs: support git worktrees

Fixes golang/go#58218

Change-Id: Ia155b26514557cf822caf37e727e5a410b0a36a6
Reviewed-on: https://go-review.googlesource.com/c/go/+/736260
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

3 files changed, 170 insertions, 55 deletions

diff --git a/src/cmd/go/internal/vcs/vcs.go b/src/cmd/go/internal/vcs/vcs.go
index 98ed77d80d..5613e79e7c 100644
--- a/src/cmd/go/internal/vcs/vcs.go
+++ b/src/cmd/go/internal/vcs/vcs.go
@@ -35,10 +35,10 @@ import (
 // A Cmd describes how to use a version control system
 // like Mercurial, Git, or Subversion.
 type Cmd struct {
-	Name      string
-	Cmd       string     // name of binary to invoke command
-	Env       []string   // any environment values to set/override
-	RootNames []rootName // filename and mode indicating the root of a checkout directory
+	Name  string
+	Cmd   string      // name of binary to invoke command
+	Env   []string    // any environment values to set/override
+	Roots []isVCSRoot // filters to identify repository root directories
 
 	Scheme  []string
 	PingCmd string
@@ -149,8 +149,8 @@ var vcsHg = &Cmd{
 	// HGPLAIN=+strictflags turns off additional output that a user may have
 	// enabled via config options or certain extensions.
 	Env: []string{"HGPLAIN=+strictflags"},
-	RootNames: []rootName{
-		{filename: ".hg", isDir: true},
+	Roots: []isVCSRoot{
+		vcsDirRoot(".hg"),
 	},
 
 	Scheme:  []string{"https", "http", "ssh"},
@@ -214,8 +214,8 @@ func parseRevTime(out []byte) (string, time.Time, error) {
 var vcsGit = &Cmd{
 	Name: "Git",
 	Cmd:  "git",
-	RootNames: []rootName{
-		{filename: ".git", isDir: true},
+	Roots: []isVCSRoot{
+		vcsGitRoot{},
 	},
 
 	Scheme: []string{"git", "https", "http", "git+ssh", "ssh"},
@@ -262,8 +262,8 @@ func gitStatus(vcsGit *Cmd, rootDir string) (Status, error) {
 var vcsBzr = &Cmd{
 	Name: "Bazaar",
 	Cmd:  "bzr",
-	RootNames: []rootName{
-		{filename: ".bzr", isDir: true},
+	Roots: []isVCSRoot{
+		vcsDirRoot(".bzr"),
 	},
 
 	Scheme:  []string{"https", "http", "bzr", "bzr+ssh"},
@@ -332,8 +332,8 @@ func bzrStatus(vcsBzr *Cmd, rootDir string) (Status, error) {
 var vcsSvn = &Cmd{
 	Name: "Subversion",
 	Cmd:  "svn",
-	RootNames: []rootName{
-		{filename: ".svn", isDir: true},
+	Roots: []isVCSRoot{
+		vcsDirRoot(".svn"),
 	},
 
 	// There is no tag command in subversion.
@@ -381,9 +381,9 @@ const fossilRepoName = ".fossil"
 var vcsFossil = &Cmd{
 	Name: "Fossil",
 	Cmd:  "fossil",
-	RootNames: []rootName{
-		{filename: ".fslckout", isDir: false},
-		{filename: "_FOSSIL_", isDir: false},
+	Roots: []isVCSRoot{
+		vcsFileRoot(".fslckout"),
+		vcsFileRoot("_FOSSIL_"),
 	},
 
 	Scheme: []string{"https", "http"},
@@ -592,7 +592,7 @@ func FromDir(dir, srcRoot string) (repoDir string, vcsCmd *Cmd, err error) {
 	origDir := dir
 	for len(dir) > len(srcRoot) {
 		for _, vcs := range vcsList {
-			if isVCSRoot(dir, vcs.RootNames) {
+			if isVCSRootDir(dir, vcs.Roots) {
 				if vcsCmd == nil {
 					// Record first VCS we find.
 					vcsCmd = vcs
@@ -631,22 +631,71 @@ func FromDir(dir, srcRoot string) (repoDir string, vcsCmd *Cmd, err error) {
 	return repoDir, vcsCmd, nil
 }
 
-// isVCSRoot identifies a VCS root by checking whether the directory contains
-// any of the listed root names.
-func isVCSRoot(dir string, rootNames []rootName) bool {
-	for _, root := range rootNames {
-		fi, err := os.Stat(filepath.Join(dir, root.filename))
-		if err == nil && fi.IsDir() == root.isDir {
+// isVCSRootDir reports whether dir is a VCS root according to roots.
+func isVCSRootDir(dir string, roots []isVCSRoot) bool {
+	for _, root := range roots {
+		if root.isRoot(dir) {
 			return true
 		}
 	}
-
 	return false
 }
 
-type rootName struct {
-	filename string
-	isDir    bool
+type isVCSRoot interface {
+	isRoot(dir string) bool
+}
+
+// vcsFileRoot identifies a VCS root by the presence of a regular file.
+type vcsFileRoot string
+
+func (vfr vcsFileRoot) isRoot(dir string) bool {
+	fi, err := os.Stat(filepath.Join(dir, string(vfr)))
+	return err == nil && fi.Mode().IsRegular()
+}
+
+// vcsDirRoot identifies a VCS root by the presence of a directory.
+type vcsDirRoot string
+
+func (vdr vcsDirRoot) isRoot(dir string) bool {
+	fi, err := os.Stat(filepath.Join(dir, string(vdr)))
+	return err == nil && fi.IsDir()
+}
+
+// vcsGitRoot identifies a Git root by the presence of a .git directory or a .git worktree file.
+// See https://go.dev/issue/58218.
+type vcsGitRoot struct{}
+
+func (vcsGitRoot) isRoot(dir string) bool {
+	path := filepath.Join(dir, ".git")
+	fi, err := os.Stat(path)
+	if err != nil {
+		return false
+	}
+	if fi.IsDir() {
+		return true
+	}
+	// Is it a git worktree file?
+	// The format is "gitdir: <path>\n".
+	if !fi.Mode().IsRegular() || fi.Size() == 0 || fi.Size() > 4096 {
+		return false
+	}
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		return false
+	}
+	rest, ok := strings.CutPrefix(string(raw), "gitdir:")
+	if !ok {
+		return false
+	}
+	gitdir := strings.TrimSpace(rest)
+	if gitdir == "" {
+		return false
+	}
+	if !filepath.IsAbs(gitdir) {
+		gitdir = filepath.Join(dir, gitdir)
+	}
+	fi, err = os.Stat(gitdir)
+	return err == nil && fi.IsDir()
 }
 
 type vcsNotFoundError struct {
diff --git a/src/cmd/go/internal/vcs/vcs_test.go b/src/cmd/go/internal/vcs/vcs_test.go
index ab70e517e2..8da8eb2c11 100644
--- a/src/cmd/go/internal/vcs/vcs_test.go
+++ b/src/cmd/go/internal/vcs/vcs_test.go
@@ -6,7 +6,6 @@ package vcs
 
 import (
 	"errors"
-	"fmt"
 	"internal/testenv"
 	"os"
 	"path/filepath"
@@ -215,40 +214,61 @@ func TestRepoRootForImportPath(t *testing.T) {
 // Test that vcs.FromDir correctly inspects a given directory and returns the
 // right VCS and repo directory.
 func TestFromDir(t *testing.T) {
-	tempDir := t.TempDir()
+	tests := []struct {
+		name   string
+		vcs    string
+		root   string
+		create func(path string) error
+	}{
+		{"hg", "Mercurial", ".hg", mkdir},
+		{"git_dir", "Git", ".git", mkdir},
+		{"git_worktree", "Git", ".git", createGitWorktreeFile},
+		{"bzr", "Bazaar", ".bzr", mkdir},
+		{"svn", "Subversion", ".svn", mkdir},
+		{"fossil_fslckout", "Fossil", ".fslckout", touch},
+		{"fossil_FOSSIL_", "Fossil", "_FOSSIL_", touch},
+	}
 
-	for _, vcs := range vcsList {
-		for r, root := range vcs.RootNames {
-			vcsName := fmt.Sprint(vcs.Name, r)
-			dir := filepath.Join(tempDir, "example.com", vcsName, root.filename)
-			if root.isDir {
-				err := os.MkdirAll(dir, 0755)
-				if err != nil {
-					t.Fatal(err)
-				}
-			} else {
-				err := os.MkdirAll(filepath.Dir(dir), 0755)
-				if err != nil {
-					t.Fatal(err)
-				}
-				f, err := os.Create(dir)
-				if err != nil {
-					t.Fatal(err)
-				}
-				f.Close()
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tempDir := t.TempDir()
+			repoDir := filepath.Join(tempDir, "example.com")
+			if err := mkdir(repoDir); err != nil {
+				t.Fatal(err)
 			}
-
-			wantRepoDir := filepath.Dir(dir)
-			gotRepoDir, gotVCS, err := FromDir(dir, tempDir)
+			rootPath := filepath.Join(repoDir, tt.root)
+			if err := tt.create(rootPath); err != nil {
+				t.Fatal(err)
+			}
+			gotRepoDir, gotVCS, err := FromDir(repoDir, tempDir)
 			if err != nil {
-				t.Errorf("FromDir(%q, %q): %v", dir, tempDir, err)
-				continue
+				t.Fatal(err)
 			}
-			if gotRepoDir != wantRepoDir || gotVCS.Name != vcs.Name {
-				t.Errorf("FromDir(%q, %q) = RepoDir(%s), VCS(%s); want RepoDir(%s), VCS(%s)", dir, tempDir, gotRepoDir, gotVCS.Name, wantRepoDir, vcs.Name)
+			if gotRepoDir != repoDir {
+				t.Errorf("RepoDir = %q, want %q", gotRepoDir, repoDir)
 			}
-		}
+			if gotVCS.Name != tt.vcs {
+				t.Errorf("VCS = %q, want %q", gotVCS.Name, tt.vcs)
+			}
+		})
+	}
+}
+
+func mkdir(path string) error {
+	return os.Mkdir(path, 0o755)
+}
+
+func touch(path string) error {
+	return os.WriteFile(path, nil, 0o644)
+}
+
+func createGitWorktreeFile(path string) error {
+	gitdir := path + ".worktree"
+	// gitdir must point to a real directory
+	if err := mkdir(gitdir); err != nil {
+		return err
 	}
+	return os.WriteFile(path, []byte("gitdir: "+gitdir+"\n"), 0o644)
 }
 
 func TestIsSecure(t *testing.T) {
diff --git a/src/cmd/go/testdata/script/version_buildvcs_git_worktree.txt b/src/cmd/go/testdata/script/version_buildvcs_git_worktree.txt
new file mode 100644
index 0000000000..651d1699ce
--- /dev/null
+++ b/src/cmd/go/testdata/script/version_buildvcs_git_worktree.txt
@@ -0,0 +1,46 @@
+# Test that 'go build' stamps VCS information when building from a git worktree.
+# See https://go.dev/issue/58218.
+
+[!git] skip
+[short] skip
+
+# Create repo with a commit.
+cd repo
+exec git init
+exec git config user.email g.o.p.h.e.r@go.dev
+exec git config user.name Gopher
+exec git add -A
+exec git commit -m 'initial commit'
+
+# Sanity check: building from main repo includes VCS info.
+go build -o main.exe .
+go version -m main.exe
+stdout '^\tbuild\tvcs=git$'
+stdout '^\tbuild\tvcs.modified=false$'
+
+# Create a worktree and build from it.
+exec git worktree add ../worktree HEAD
+cd ../worktree
+go build -o worktree.exe .
+go version -m worktree.exe
+stdout '^\tbuild\tvcs=git$'
+stdout '^\tbuild\tvcs.modified=false$'
+
+# Verify that vcs.modified is detected in the worktree.
+cp ../changed.go a.go
+go build -o modified.exe .
+go version -m modified.exe
+stdout '^\tbuild\tvcs.modified=true$'
+
+-- repo/go.mod --
+module example.com/worktree
+
+go 1.18
+-- repo/a.go --
+package main
+
+func main() {}
+-- changed.go --
+package main
+
+func main() { _ = 1 }