cmd/go/internal/modfetch/codehost: fix pseudoversions for non-semver tags and tags on other branches

Pseudoversion determination depends in part on the results from gitRepo.RecentTag, which currently invokes:

git describe --first-parent --always --abbrev=0 --match <prefix>v[0-9]*.[0-9]*.[0-9]* --tags <rev>

The comment at https://github.com/golang/go/issues/27171#issuecomment-470134255 describes some problems with the current approach.

One problem is Docker and other repos can have tags that are not valid semver tags but that still match a glob pattern of v[0-9]*.[0-9]*.[0-9]* which are found by 'git describe' but then rejected by cmd/go, and hence those repos currently can end up with v0.0.0 pseudoversions instead of finding a proper semver tag to use as input to building a pseudoversion  (when then causes problems when the v0.0.0 pseudoversion is fed into MVS). An example problematic tag is a date-based tag such as 'v18.06.16', which matches the glob pattern, but is not a valid semver tag (due to the leading 0 in '06').

Issues #31673, #31287, and #27171 also describe problems where the '--first-parent' argument to 'git describe' cause the current approach to miss relevant semver tags that were created on a separate branch and then subsequently merged to master.

In #27171, Bryan described the base tag that is supposed to be used for pseudoversions as:

"It is intended to be the semantically-latest tag that appears on any commit that is a (transitive) parent of the commit with the given hash, regardless of branches. (The pseudo-version is supposed to sort after every version — tagged or otherwise — that came before it, but before the next tag that a human might plausibly want to apply to the branch.)"

This CL solves the glob problem and tags-on-other-branches problem more directly than the current approach: this CL gets the full list of tags that have been merged into the specific revision of interest, and then sorts and filters the results in cmd/go to select the semantically-latest valid semver tag.

Fixes #31673
Fixes #31287
Updates #27171

Change-Id: I7c3e6b46b2b21dd60562cf2893b6bd2afaae61d5
Reviewed-on: https://go-review.googlesource.com/c/go/+/174061
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

1 files changed, 29 insertions, 4 deletions

diff --git a/src/cmd/go/internal/modfetch/codehost/git.go b/src/cmd/go/internal/modfetch/codehost/git.go
index 5273e633b5..55627cb72a 100644
--- a/src/cmd/go/internal/modfetch/codehost/git.go
+++ b/src/cmd/go/internal/modfetch/codehost/git.go
@@ -19,6 +19,7 @@ import (
 
 	"cmd/go/internal/lockedfile"
 	"cmd/go/internal/par"
+	"cmd/go/internal/semver"
 )
 
 // GitRepo returns the code repository at the given Git remote reference.
@@ -652,16 +653,40 @@ func (r *gitRepo) RecentTag(rev, prefix string) (tag string, err error) {
 	}
 	rev = info.Name // expand hash prefixes
 
-	// describe sets tag and err using 'git describe' and reports whether the
+	// describe sets tag and err using 'git for-each-ref' and reports whether the
 	// result is definitive.
 	describe := func() (definitive bool) {
 		var out []byte
-		out, err = Run(r.dir, "git", "describe", "--first-parent", "--always", "--abbrev=0", "--match", prefix+"v[0-9]*.[0-9]*.[0-9]*", "--tags", rev)
+		out, err = Run(r.dir, "git", "for-each-ref", "--format", "%(refname)", "refs/tags", "--merged", rev)
 		if err != nil {
-			return true // Because we use "--always", describe should never fail.
+			return true
+		}
+
+		// prefixed tags aren't valid semver tags so compare without prefix, but only tags with correct prefix
+		var highest string
+		for _, line := range strings.Split(string(out), "\n") {
+			line = strings.TrimSpace(line)
+			// git do support lstrip in for-each-ref format, but it was added in v2.13.0. Stripping here
+			// instead gives support for git v2.7.0.
+			if !strings.HasPrefix(line, "refs/tags/") {
+				continue
+			}
+			line = line[len("refs/tags/"):]
+
+			if !strings.HasPrefix(line, prefix) {
+				continue
+			}
+
+			semtag := line[len(prefix):]
+			if semver.IsValid(semtag) {
+				highest = semver.Max(highest, semtag)
+			}
+		}
+
+		if highest != "" {
+			tag = prefix + highest
 		}
 
-		tag = string(bytes.TrimSpace(out))
 		return tag != "" && !AllHex(tag)
 	}