Use full output of git show-ref --tags to get tags for PushUpdateAddTag (#19235)

Strangely #19038 appears to relate to an issue whereby a tag appears to
be listed in `git show-ref --tags` but then does not appear when `git
show-ref --tags -- short_name` is called.

As a solution though I propose to stop the second call as it is
unnecessary and only likely to cause problems.

I've also noticed that the tags calls are wildly inefficient and aren't using the common cat-files - so these have been added.

I've also noticed that the git commit-graph is not being written on mirroring - so I've also added writing this to the migration which should improve mirror rendering somewhat. 

Fix #19038

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>

modules/git/repo_tag_gogit.go

@@ -11,6 +11,8 @@ package git
 import (
 	"strings"
 
+	"code.gitea.io/gitea/modules/log"
+
 	"github.com/go-git/go-git/v5/plumbing"
 )
 
@@ -53,3 +55,83 @@ func (repo *Repository) GetTags(skip, limit int) ([]string, error) {
 
 	return tagNames, nil
 }
+
+// GetTagType gets the type of the tag, either commit (simple) or tag (annotated)
+func (repo *Repository) GetTagType(id SHA1) (string, error) {
+	// Get tag type
+	obj, err := repo.gogitRepo.Object(plumbing.AnyObject, id)
+	if err != nil {
+		if err == plumbing.ErrReferenceNotFound {
+			return "", &ErrNotExist{ID: id.String()}
+		}
+		return "", err
+	}
+
+	return obj.Type().String(), nil
+}
+
+func (repo *Repository) getTag(tagID SHA1, name string) (*Tag, error) {
+	t, ok := repo.tagCache.Get(tagID.String())
+	if ok {
+		log.Debug("Hit cache: %s", tagID)
+		tagClone := *t.(*Tag)
+		tagClone.Name = name // This is necessary because lightweight tags may have same id
+		return &tagClone, nil
+	}
+
+	tp, err := repo.GetTagType(tagID)
+	if err != nil {
+		return nil, err
+	}
+
+	// Get the commit ID and tag ID (may be different for annotated tag) for the returned tag object
+	commitIDStr, err := repo.GetTagCommitID(name)
+	if err != nil {
+		// every tag should have a commit ID so return all errors
+		return nil, err
+	}
+	commitID, err := NewIDFromString(commitIDStr)
+	if err != nil {
+		return nil, err
+	}
+
+	// If type is "commit, the tag is a lightweight tag
+	if ObjectType(tp) == ObjectCommit {
+		commit, err := repo.GetCommit(commitIDStr)
+		if err != nil {
+			return nil, err
+		}
+		tag := &Tag{
+			Name:    name,
+			ID:      tagID,
+			Object:  commitID,
+			Type:    tp,
+			Tagger:  commit.Committer,
+			Message: commit.Message(),
+		}
+
+		repo.tagCache.Set(tagID.String(), tag)
+		return tag, nil
+	}
+
+	gogitTag, err := repo.gogitRepo.TagObject(tagID)
+	if err != nil {
+		if err == plumbing.ErrReferenceNotFound {
+			return nil, &ErrNotExist{ID: tagID.String()}
+		}
+
+		return nil, err
+	}
+
+	tag := &Tag{
+		Name:    name,
+		ID:      tagID,
+		Object:  gogitTag.Target,
+		Type:    tp,
+		Tagger:  &gogitTag.Tagger,
+		Message: gogitTag.Message,
+	}
+
+	repo.tagCache.Set(tagID.String(), tag)
+	return tag, nil
+}