cmd/go: add Mercurial based version stamping for binaries

This CL adds a local only VCS lookup for Mercurial.
It fixes a bug in pkg.go by passing in the repo directory to
the LookupLocal function instead of the module directory. It could be
the case that a binary is built in a subdirectory of the repo.

For: #50603
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-windows-amd64-longtest
Change-Id: Ic36b5a361a8ba3b0ba1a6968cde5f5263c9c8dd0
Reviewed-on: https://go-review.googlesource.com/c/go/+/609155
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@golang.org>

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

@@ -2494,7 +2494,7 @@ func (p *Package) setBuildInfo(ctx context.Context, autoVCS bool) {
 		}
 		appendSetting("vcs.modified", strconv.FormatBool(st.Uncommitted))
 		// Determine the correct version of this module at the current revision and update the build metadata accordingly.
-		repo := modfetch.LookupLocal(ctx, p.Module.Dir)
+		repo := modfetch.LookupLocal(ctx, repoDir)
 		revInfo, err := repo.Stat(ctx, st.Revision)
 		if err != nil {
 			goto omitVCS

src/cmd/go/internal/modfetch/codehost/vcs.go

@@ -70,6 +70,7 @@ type vcsRepo struct {
 	remote string
 	cmd    *vcsCmd
 	dir    string
+	local  bool
 
 	tagsOnce sync.Once
 	tags     map[string]bool
@@ -85,15 +86,27 @@ func newVCSRepo(ctx context.Context, vcs, remote string, local bool) (Repo, erro
 	if vcs == "git" {
 		return newGitRepo(ctx, remote, local)
 	}
+	r := &vcsRepo{remote: remote, local: local}
 	cmd := vcsCmds[vcs]
 	if cmd == nil {
 		return nil, fmt.Errorf("unknown vcs: %s %s", vcs, remote)
 	}
+	r.cmd = cmd
+	if local {
+		info, err := os.Stat(remote)
+		if err != nil {
+			return nil, err
+		}
+		if !info.IsDir() {
+			return nil, fmt.Errorf("%s exists but is not a directory", remote)
+		}
+		r.dir = remote
+		r.mu.Path = r.dir + ".lock"
+		return r, nil
+	}
 	if !strings.Contains(remote, "://") {
 		return nil, fmt.Errorf("invalid vcs remote: %s %s", vcs, remote)
 	}
-
-	r := &vcsRepo{remote: remote, cmd: cmd}
 	var err error
 	r.dir, r.mu.Path, err = WorkDir(ctx, vcsWorkDirType+vcs, r.remote)
 	if err != nil {
@@ -341,6 +354,11 @@ func (r *vcsRepo) Stat(ctx context.Context, rev string) (*RevInfo, error) {
 		rev = r.cmd.latest
 	}
 	r.branchesOnce.Do(func() { r.loadBranches(ctx) })
+	if r.local {
+		// Ignore the badLocalRevRE precondition in local only mode.
+		// We cannot fetch latest upstream changes so only serve what's in the local cache.
+		return r.statLocal(ctx, rev)
+	}
 	revOK := (r.cmd.badLocalRevRE == nil || !r.cmd.badLocalRevRE.MatchString(rev)) && !r.branches[rev]
 	if revOK {
 		if info, err := r.statLocal(ctx, rev); err == nil {

src/cmd/go/testdata/script/version_buildvcs_hg.txt

@@ -14,6 +14,7 @@ cd repo/a
 go install
 go version -m $GOBIN/a$GOEXE
 ! stdout hgrevision
+stdout '\s+mod\s+example.com/a\s+\(devel\)'
 rm $GOBIN/a$GOEXE
 
 # If there is a repository, but it can't be used for some reason,
@@ -40,17 +41,23 @@ go version -m $GOBIN/a$GOEXE
 stdout '^\tbuild\tvcs.revision=0000000000000000000000000000000000000000$'
 stdout '^\tbuild\tvcs.time=1970-01-01T00:00:00Z$'
 stdout '^\tbuild\tvcs.modified=true$'
+stdout '\s+mod\s+example.com/a\s+v0.0.0-19700101000000-000000000000\+dirty'
 cd ..
 
 # Revision and commit time are tagged for repositories with commits.
 exec hg add a README
 exec hg commit -m 'initial commit' --user test-user --date '2024-07-31T01:21:27+00:00'
+exec hg tag v1.2.3
+# Switch back to the tagged branch.
+# Tagging a commit causes a new commit to be created. (See https://repo.mercurial-scm.org/hg/help/revsets)
+exec hg update '.~1'
 cd a
 go install
 go version -m $GOBIN/a$GOEXE
 stdout '^\tbuild\tvcs.revision=71eaed52daeaafea83cb604f75b0a0336ef2c345$'
 stdout '^\tbuild\tvcs.time=2024-07-31T01:21:27Z$'
 stdout '^\tbuild\tvcs.modified=false$'
+stdout '\s+mod\s+example.com/a\s+v1.2.3\s+'
 rm $GOBIN/a$GOEXE
 
 # Add an extra commit and then back off of it to show that the hash is
@@ -69,19 +76,22 @@ go version -m $GOBIN/a$GOEXE
 stdout '^\tbuild\tvcs.revision=71eaed52daeaafea83cb604f75b0a0336ef2c345$'
 stdout '^\tbuild\tvcs.time=2024-07-31T01:21:27Z$'
 stdout '^\tbuild\tvcs.modified=false$'
+stdout '\s+mod\s+example.com/a\s+v1.2.3\s+'
 rm $GOBIN/a$GOEXE
 
 # Building with -buildvcs=false suppresses the info.
 go install -buildvcs=false
 go version -m $GOBIN/a$GOEXE
 ! stdout hgrevision
+stdout '\s+mod\s+example.com/a\s+\(devel\)'
 rm $GOBIN/a$GOEXE
 
 # An untracked file is shown as uncommitted, even if it isn't part of the build.
 cp ../../outside/empty.txt .
 go install
 go version -m $GOBIN/a$GOEXE
 stdout '^\tbuild\tvcs.modified=true$'
+stdout '\s+mod\s+example.com/a\s+v1.2.3\+dirty\s+'
 rm empty.txt
 rm $GOBIN/a$GOEXE
 
@@ -90,6 +100,7 @@ cp ../../outside/empty.txt ../README
 go install
 go version -m $GOBIN/a$GOEXE
 stdout '^\tbuild\tvcs.modified=true$'
+stdout '\s+mod\s+example.com/a\s+v1.2.3\+dirty\s+'
 exec hg revert ../README
 rm $GOBIN/a$GOEXE