[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_base.go

@@ -1,6 +1,116 @@
-// Copyright 2021 The Gitea Authors. All rights reserved.
+// Copyright 2015 The Gogs Authors. All rights reserved.
+// Copyright 2017 The Gitea Authors. All rights reserved.
 // SPDX-License-Identifier: MIT
 
 package git
 
-var isGogit bool
+import (
+	"bufio"
+	"context"
+	"errors"
+	"path/filepath"
+
+	"code.gitea.io/gitea/modules/log"
+)
+
+// Repository represents a Git repository.
+type Repository struct {
+	Path string
+
+	tagCache *ObjectCache
+
+	gpgSettings *GPGSettings
+
+	batchInUse  bool
+	batchCancel context.CancelFunc
+	batchReader *bufio.Reader
+	batchWriter WriteCloserError
+
+	checkInUse  bool
+	checkCancel context.CancelFunc
+	checkReader *bufio.Reader
+	checkWriter WriteCloserError
+
+	Ctx             context.Context
+	LastCommitCache *LastCommitCache
+
+	objectFormat ObjectFormat
+}
+
+// openRepositoryWithDefaultContext opens the repository at the given path with DefaultContext.
+func openRepositoryWithDefaultContext(repoPath string) (*Repository, error) {
+	return OpenRepository(DefaultContext, repoPath)
+}
+
+// OpenRepository opens the repository at the given path with the provided context.
+func OpenRepository(ctx context.Context, repoPath string) (*Repository, error) {
+	repoPath, err := filepath.Abs(repoPath)
+	if err != nil {
+		return nil, err
+	} else if !isDir(repoPath) {
+		return nil, errors.New("no such file or directory")
+	}
+
+	// Now because of some insanity with git cat-file not immediately failing if not run in a valid git directory we need to run git rev-parse first!
+	if err := EnsureValidGitRepository(ctx, repoPath); err != nil {
+		return nil, err
+	}
+
+	repo := &Repository{
+		Path:     repoPath,
+		tagCache: newObjectCache(),
+		Ctx:      ctx,
+	}
+
+	repo.batchWriter, repo.batchReader, repo.batchCancel = CatFileBatch(ctx, repoPath)
+	repo.checkWriter, repo.checkReader, repo.checkCancel = CatFileBatchCheck(ctx, repoPath)
+
+	return repo, nil
+}
+
+// CatFileBatch obtains a CatFileBatch for this repository
+func (repo *Repository) CatFileBatch(ctx context.Context) (WriteCloserError, *bufio.Reader, func()) {
+	if repo.batchCancel == nil || repo.batchInUse {
+		log.Debug("Opening temporary cat file batch for: %s", repo.Path)
+		return CatFileBatch(ctx, repo.Path)
+	}
+	repo.batchInUse = true
+	return repo.batchWriter, repo.batchReader, func() {
+		repo.batchInUse = false
+	}
+}
+
+// CatFileBatchCheck obtains a CatFileBatchCheck for this repository
+func (repo *Repository) CatFileBatchCheck(ctx context.Context) (WriteCloserError, *bufio.Reader, func()) {
+	if repo.checkCancel == nil || repo.checkInUse {
+		log.Debug("Opening temporary cat file batch-check for: %s", repo.Path)
+		return CatFileBatchCheck(ctx, repo.Path)
+	}
+	repo.checkInUse = true
+	return repo.checkWriter, repo.checkReader, func() {
+		repo.checkInUse = false
+	}
+}
+
+func (repo *Repository) Close() error {
+	if repo == nil {
+		return nil
+	}
+	if repo.batchCancel != nil {
+		repo.batchCancel()
+		repo.batchReader = nil
+		repo.batchWriter = nil
+		repo.batchCancel = nil
+		repo.batchInUse = false
+	}
+	if repo.checkCancel != nil {
+		repo.checkCancel()
+		repo.checkCancel = nil
+		repo.checkReader = nil
+		repo.checkWriter = nil
+		repo.checkInUse = false
+	}
+	repo.LastCommitCache = nil
+	repo.tagCache = nil
+	return nil
+}