refactor!: remove go-git backend (#39487)

Removes the go-git backend so every build uses the git CLI backend. Its
Windows performance advantage is gone, it lacks SHA-256 support, and it
breaks repositories on Windows.

The performance changes moved to
https://github.com/go-gitea/gitea/pull/39526.

Fixes https://github.com/go-gitea/gitea/issues/38359
Fixes https://github.com/go-gitea/gitea/issues/34694

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/git/repo_commit.go

@@ -7,6 +7,7 @@ package git
 import (
 	"bytes"
 	"context"
+	"errors"
 	"io"
 	"strconv"
 	"strings"
@@ -458,3 +459,124 @@ func (repo *Repository) GetCommitBranchStart(ctx context.Context, env []string,
 
 	return "", nil
 }
+
+// GetRefCommitID returns the last commit ID string of given reference (branch or tag).
+func (repo *Repository) GetRefCommitID(ctx context.Context, name string) (string, error) {
+	batch, cancel, err := repo.CatFileBatch()
+	if err != nil {
+		return "", err
+	}
+	defer cancel()
+	info, err := batch.QueryInfo(name)
+	if IsErrNotExist(err) {
+		return "", ErrNotExist{name, ""}
+	} else if err != nil {
+		return "", err
+	}
+	return info.ID, nil
+}
+
+func (repo *Repository) getCommit(_ context.Context, id ObjectID) (*Commit, error) {
+	batch, cancel, err := repo.CatFileBatch()
+	if err != nil {
+		return nil, err
+	}
+	defer cancel()
+	return repo.getCommitWithBatch(batch, id)
+}
+
+func limitDiscardReader(rd BufferedReader, full, limit int64) (io.Reader, func() error) {
+	return io.LimitReader(rd, min(full, limit)), func() error {
+		if full > limit {
+			return DiscardFull(rd, full-limit)
+		}
+		return nil
+	}
+}
+
+func (repo *Repository) getCommitWithBatch(batch CatFileBatch, id ObjectID) (*Commit, error) {
+	info, rd, err := batch.QueryContent(id.String())
+	if err != nil {
+		if errors.Is(err, io.EOF) || IsErrNotExist(err) {
+			return nil, ErrNotExist{ID: id.String()}
+		}
+		return nil, err
+	}
+
+	switch info.Type {
+	case "missing":
+		return nil, ErrNotExist{ID: id.String()}
+	case "tag":
+		limitReader, limitDiscard := limitDiscardReader(rd, info.Size, MaxGitObjectSize)
+		data, err := io.ReadAll(limitReader)
+		if err != nil {
+			return nil, err
+		}
+		if err = limitDiscard(); 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
+		}
+		return repo.getCommitWithBatch(batch, tag.Object)
+	case "commit":
+		limitReader, limitDiscard := limitDiscardReader(rd, info.Size, MaxGitObjectSize)
+		commit, err := CommitFromReader(id, limitReader)
+		if err != nil {
+			return nil, err
+		}
+		if err = limitDiscard(); err != nil {
+			return nil, err
+		}
+		_, err = rd.Discard(1)
+		if err != nil {
+			return nil, err
+		}
+
+		return commit, nil
+	default:
+		if info.Type != "blob" && info.Type != "tree" {
+			setting.PanicInDevOrTesting("Unknown cat-file object type %s for object %s in repo %s", info.Type, id.String(), repo.LogString())
+		}
+		if err := DiscardFull(rd, info.Size+1); err != nil {
+			return nil, err
+		}
+		return nil, ErrNotExist{
+			ID: id.String(),
+		}
+	}
+}
+
+// ConvertToGitID returns a git object ID from the git ref, it doesn't guarantee the returned ID really exists
+func (repo *Repository) ConvertToGitID(ctx context.Context, ref string) (ObjectID, error) {
+	objectFormat, err := repo.GetObjectFormat(ctx)
+	if err != nil {
+		return nil, err
+	}
+	if IsStringValidObjectID(objectFormat, ref) {
+		id, err := NewIDFromString(ref)
+		if err == nil {
+			return id, nil
+		}
+	}
+
+	batch, cancel, err := repo.CatFileBatch()
+	if err != nil {
+		return nil, err
+	}
+	defer cancel()
+	info, err := batch.QueryInfo(ref)
+	if err != nil {
+		if IsErrNotExist(err) {
+			return nil, ErrNotExist{ref, ""}
+		}
+		return nil, err
+	}
+
+	return MustIDFromString(info.ID), nil
+}