[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_branch.go

@@ -5,10 +5,15 @@
 package git
 
 import (
+	"bufio"
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"strings"
+
+	"code.gitea.io/gitea/modules/log"
 )
 
 // BranchPrefix base dir of the branch information file store on git
@@ -157,3 +162,180 @@ func (repo *Repository) RenameBranch(from, to string) error {
 	_, _, err := NewCommand(repo.Ctx, "branch", "-m").AddDynamicArguments(from, to).RunStdString(&RunOpts{Dir: repo.Path})
 	return err
 }
+
+// IsObjectExist returns true if given reference exists in the repository.
+func (repo *Repository) IsObjectExist(name string) bool {
+	if name == "" {
+		return false
+	}
+
+	wr, rd, cancel := repo.CatFileBatchCheck(repo.Ctx)
+	defer cancel()
+	_, err := wr.Write([]byte(name + "\n"))
+	if err != nil {
+		log.Debug("Error writing to CatFileBatchCheck %v", err)
+		return false
+	}
+	sha, _, _, err := ReadBatchLine(rd)
+	return err == nil && bytes.HasPrefix(sha, []byte(strings.TrimSpace(name)))
+}
+
+// IsReferenceExist returns true if given reference exists in the repository.
+func (repo *Repository) IsReferenceExist(name string) bool {
+	if name == "" {
+		return false
+	}
+
+	wr, rd, cancel := repo.CatFileBatchCheck(repo.Ctx)
+	defer cancel()
+	_, err := wr.Write([]byte(name + "\n"))
+	if err != nil {
+		log.Debug("Error writing to CatFileBatchCheck %v", err)
+		return false
+	}
+	_, _, _, err = ReadBatchLine(rd)
+	return err == nil
+}
+
+// IsBranchExist returns true if given branch exists in current repository.
+func (repo *Repository) IsBranchExist(name string) bool {
+	if repo == nil || name == "" {
+		return false
+	}
+
+	return repo.IsReferenceExist(BranchPrefix + name)
+}
+
+// GetBranchNames returns branches from the repository, skipping "skip" initial branches and
+// returning at most "limit" branches, or all branches if "limit" is 0.
+func (repo *Repository) GetBranchNames(skip, limit int) ([]string, int, error) {
+	return callShowRef(repo.Ctx, repo.Path, BranchPrefix, TrustedCmdArgs{BranchPrefix, "--sort=-committerdate"}, skip, limit)
+}
+
+// WalkReferences walks all the references from the repository
+// refType should be empty, ObjectTag or ObjectBranch. All other values are equivalent to empty.
+func (repo *Repository) WalkReferences(refType ObjectType, skip, limit int, walkfn func(sha1, refname string) error) (int, error) {
+	var args TrustedCmdArgs
+	switch refType {
+	case ObjectTag:
+		args = TrustedCmdArgs{TagPrefix, "--sort=-taggerdate"}
+	case ObjectBranch:
+		args = TrustedCmdArgs{BranchPrefix, "--sort=-committerdate"}
+	}
+
+	return WalkShowRef(repo.Ctx, repo.Path, args, skip, limit, walkfn)
+}
+
+// callShowRef return refs, if limit = 0 it will not limit
+func callShowRef(ctx context.Context, repoPath, trimPrefix string, extraArgs TrustedCmdArgs, skip, limit int) (branchNames []string, countAll int, err error) {
+	countAll, err = WalkShowRef(ctx, repoPath, extraArgs, skip, limit, func(_, branchName string) error {
+		branchName = strings.TrimPrefix(branchName, trimPrefix)
+		branchNames = append(branchNames, branchName)
+
+		return nil
+	})
+	return branchNames, countAll, err
+}
+
+func WalkShowRef(ctx context.Context, repoPath string, extraArgs TrustedCmdArgs, skip, limit int, walkfn func(sha1, refname string) error) (countAll int, err error) {
+	stdoutReader, stdoutWriter := io.Pipe()
+	defer func() {
+		_ = stdoutReader.Close()
+		_ = stdoutWriter.Close()
+	}()
+
+	go func() {
+		stderrBuilder := &strings.Builder{}
+		args := TrustedCmdArgs{"for-each-ref", "--format=%(objectname) %(refname)"}
+		args = append(args, extraArgs...)
+		err := NewCommand(ctx, args...).Run(&RunOpts{
+			Dir:    repoPath,
+			Stdout: stdoutWriter,
+			Stderr: stderrBuilder,
+		})
+		if err != nil {
+			if stderrBuilder.Len() == 0 {
+				_ = stdoutWriter.Close()
+				return
+			}
+			_ = stdoutWriter.CloseWithError(ConcatenateError(err, stderrBuilder.String()))
+		} else {
+			_ = stdoutWriter.Close()
+		}
+	}()
+
+	i := 0
+	bufReader := bufio.NewReader(stdoutReader)
+	for i < skip {
+		_, isPrefix, err := bufReader.ReadLine()
+		if err == io.EOF {
+			return i, nil
+		}
+		if err != nil {
+			return 0, err
+		}
+		if !isPrefix {
+			i++
+		}
+	}
+	for limit == 0 || i < skip+limit {
+		// The output of show-ref is simply a list:
+		// <sha> SP <ref> LF
+		sha, err := bufReader.ReadString(' ')
+		if err == io.EOF {
+			return i, nil
+		}
+		if err != nil {
+			return 0, err
+		}
+
+		branchName, err := bufReader.ReadString('\n')
+		if err == io.EOF {
+			// This shouldn't happen... but we'll tolerate it for the sake of peace
+			return i, nil
+		}
+		if err != nil {
+			return i, err
+		}
+
+		if len(branchName) > 0 {
+			branchName = branchName[:len(branchName)-1]
+		}
+
+		if len(sha) > 0 {
+			sha = sha[:len(sha)-1]
+		}
+
+		err = walkfn(sha, branchName)
+		if err != nil {
+			return i, err
+		}
+		i++
+	}
+	// count all refs
+	for limit != 0 {
+		_, isPrefix, err := bufReader.ReadLine()
+		if err == io.EOF {
+			return i, nil
+		}
+		if err != nil {
+			return 0, err
+		}
+		if !isPrefix {
+			i++
+		}
+	}
+	return i, nil
+}
+
+// GetRefsBySha returns all references filtered with prefix that belong to a sha commit hash
+func (repo *Repository) GetRefsBySha(sha, prefix string) ([]string, error) {
+	var revList []string
+	_, err := WalkShowRef(repo.Ctx, repo.Path, nil, 0, 0, func(walkSha, refname string) error {
+		if walkSha == sha && strings.HasPrefix(refname, prefix) {
+			revList = append(revList, refname)
+		}
+		return nil
+	})
+	return revList, err
+}