cmd/go: pass --no-decorate when listing git tags for a commit

This avoids a parse error when the user's global .gitconfig sets
log.decorate to true.

Fixes #51312.

Change-Id: Ic47b0f604c0c3a404ec50d6e09f4e138045ac2f2
Reviewed-on: https://go-review.googlesource.com/c/go/+/387835
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

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

@@ -447,7 +447,7 @@ func (r *gitRepo) fetchRefsLocked() error {
 // statLocal returns a RevInfo describing rev in the local git repository.
 // It uses version as info.Version.
 func (r *gitRepo) statLocal(version, rev string) (*RevInfo, error) {
-	out, err := Run(r.dir, "git", "-c", "log.showsignature=false", "log", "-n1", "--format=format:%H %ct %D", rev, "--")
+	out, err := Run(r.dir, "git", "-c", "log.showsignature=false", "log", "--no-decorate", "-n1", "--format=format:%H %ct %D", rev, "--")
 	if err != nil {
 		return nil, &UnknownRevisionError{Rev: rev}
 	}

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

@@ -0,0 +1,28 @@
+env GO111MODULE=on
+
+[!net] skip
+[!exec:git] skip
+
+env GOPROXY=direct
+env HOME=$WORK/home/gopher
+
+
+go env GOPROXY
+stdout 'direct'
+
+exec git config --get log.decorate
+stdout 'full'
+
+# Test that Git log with user's global config '~/gitconfig' has log.decorate=full
+# go mod download has an error 'v1.x.y is not a tag'
+# with go1.16.14: 
+# `go1.16.14 list -m vcs-test.golang.org/git/gitrepo1.git@v1.2.3`
+# will output with error:
+# go list -m: vcs-test.golang.org/git/gitrepo1.git@v1.2.3: invalid version: unknown revision v1.2.3
+# See golang/go#51312.
+go list -m vcs-test.golang.org/git/gitrepo1.git@v1.2.3
+stdout 'vcs-test.golang.org/git/gitrepo1.git v1.2.3'
+
+-- $WORK/home/gopher/.gitconfig --
+[log]
+	decorate = full