[CHORE] Drop go-git support

See https://codeberg.org/forgejo/discussions/issues/164 for the
rationale and discussion of this change.

Everything related to the `go-git` dependency is dropped (Only a single
instance is left in a test file to test for an XSS, it requires crafting
an commit that Git itself refuses to craft). `_gogit` files have
been removed entirely, `go:build: !gogit` is removed, `XXX_nogogit.go` files
either have been renamed or had their code being merged into the
`XXX.go` file.

modules/git/repo_commit.go

@@ -5,12 +5,15 @@
 package git
 
 import (
+	"bufio"
 	"bytes"
+	"errors"
 	"io"
 	"strconv"
 	"strings"
 
 	"code.gitea.io/gitea/modules/cache"
+	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
 )
 
@@ -513,3 +516,149 @@ func (repo *Repository) AddLastCommitCache(cacheKey, fullName, sha string) error
 	}
 	return nil
 }
+
+// ResolveReference resolves a name to a reference
+func (repo *Repository) ResolveReference(name string) (string, error) {
+	stdout, _, err := NewCommand(repo.Ctx, "show-ref", "--hash").AddDynamicArguments(name).RunStdString(&RunOpts{Dir: repo.Path})
+	if err != nil {
+		if strings.Contains(err.Error(), "not a valid ref") {
+			return "", ErrNotExist{name, ""}
+		}
+		return "", err
+	}
+	stdout = strings.TrimSpace(stdout)
+	if stdout == "" {
+		return "", ErrNotExist{name, ""}
+	}
+
+	return stdout, nil
+}
+
+// GetRefCommitID returns the last commit ID string of given reference (branch or tag).
+func (repo *Repository) GetRefCommitID(name string) (string, error) {
+	wr, rd, cancel := repo.CatFileBatchCheck(repo.Ctx)
+	defer cancel()
+	_, err := wr.Write([]byte(name + "\n"))
+	if err != nil {
+		return "", err
+	}
+	shaBs, _, _, err := ReadBatchLine(rd)
+	if IsErrNotExist(err) {
+		return "", ErrNotExist{name, ""}
+	}
+
+	return string(shaBs), nil
+}
+
+// SetReference sets the commit ID string of given reference (e.g. branch or tag).
+func (repo *Repository) SetReference(name, commitID string) error {
+	_, _, err := NewCommand(repo.Ctx, "update-ref").AddDynamicArguments(name, commitID).RunStdString(&RunOpts{Dir: repo.Path})
+	return err
+}
+
+// RemoveReference removes the given reference (e.g. branch or tag).
+func (repo *Repository) RemoveReference(name string) error {
+	_, _, err := NewCommand(repo.Ctx, "update-ref", "--no-deref", "-d").AddDynamicArguments(name).RunStdString(&RunOpts{Dir: repo.Path})
+	return err
+}
+
+// IsCommitExist returns true if given commit exists in current repository.
+func (repo *Repository) IsCommitExist(name string) bool {
+	_, _, err := NewCommand(repo.Ctx, "cat-file", "-e").AddDynamicArguments(name).RunStdString(&RunOpts{Dir: repo.Path})
+	return err == nil
+}
+
+func (repo *Repository) getCommit(id ObjectID) (*Commit, error) {
+	wr, rd, cancel := repo.CatFileBatch(repo.Ctx)
+	defer cancel()
+
+	_, _ = wr.Write([]byte(id.String() + "\n"))
+
+	return repo.getCommitFromBatchReader(rd, id)
+}
+
+func (repo *Repository) getCommitFromBatchReader(rd *bufio.Reader, id ObjectID) (*Commit, error) {
+	_, typ, size, err := ReadBatchLine(rd)
+	if err != nil {
+		if errors.Is(err, io.EOF) || IsErrNotExist(err) {
+			return nil, ErrNotExist{ID: id.String()}
+		}
+		return nil, err
+	}
+
+	switch typ {
+	case "missing":
+		return nil, ErrNotExist{ID: id.String()}
+	case "tag":
+		// then we need to parse the tag
+		// and load the commit
+		data, err := io.ReadAll(io.LimitReader(rd, size))
+		if err != nil {
+			return nil, err
+		}
+		_, err = rd.Discard(1)
+		if err != nil {
+			return nil, err
+		}
+		tag, err := parseTagData(id.Type(), data)
+		if err != nil {
+			return nil, err
+		}
+
+		commit, err := tag.Commit(repo)
+		if err != nil {
+			return nil, err
+		}
+
+		return commit, nil
+	case "commit":
+		commit, err := CommitFromReader(repo, id, io.LimitReader(rd, size))
+		if err != nil {
+			return nil, err
+		}
+		_, err = rd.Discard(1)
+		if err != nil {
+			return nil, err
+		}
+
+		return commit, nil
+	default:
+		log.Debug("Unknown typ: %s", typ)
+		if err := DiscardFull(rd, size+1); err != nil {
+			return nil, err
+		}
+		return nil, ErrNotExist{
+			ID: id.String(),
+		}
+	}
+}
+
+// ConvertToGitID returns a GitHash object from a potential ID string
+func (repo *Repository) ConvertToGitID(commitID string) (ObjectID, error) {
+	objectFormat, err := repo.GetObjectFormat()
+	if err != nil {
+		return nil, err
+	}
+	if len(commitID) == objectFormat.FullLength() && objectFormat.IsValid(commitID) {
+		ID, err := NewIDFromString(commitID)
+		if err == nil {
+			return ID, nil
+		}
+	}
+
+	wr, rd, cancel := repo.CatFileBatchCheck(repo.Ctx)
+	defer cancel()
+	_, err = wr.Write([]byte(commitID + "\n"))
+	if err != nil {
+		return nil, err
+	}
+	sha, _, _, err := ReadBatchLine(rd)
+	if err != nil {
+		if IsErrNotExist(err) {
+			return nil, ErrNotExist{commitID, ""}
+		}
+		return nil, err
+	}
+
+	return MustIDFromString(string(sha)), nil
+}