Simplify how git repositories are opened (#28937)

## Purpose
This is a refactor toward building an abstraction over managing git
repositories.
Afterwards, it does not matter anymore if they are stored on the local
disk or somewhere remote.

## What this PR changes
We used `git.OpenRepository` everywhere previously.
Now, we should split them into two distinct functions:

Firstly, there are temporary repositories which do not change:

```go
git.OpenRepository(ctx, diskPath)
```

Gitea managed repositories having a record in the database in the
`repository` table are moved into the new package `gitrepo`:

```go
gitrepo.OpenRepository(ctx, repo_model.Repo)
```

Why is `repo_model.Repository` the second parameter instead of file
path?
Because then we can easily adapt our repository storage strategy.
The repositories can be stored locally, however, they could just as well
be stored on a remote server.

## Further changes in other PRs
- A Git Command wrapper on package `gitrepo` could be created. i.e.
`NewCommand(ctx, repo_model.Repository, commands...)`. `git.RunOpts{Dir:
repo.RepoPath()}`, the directory should be empty before invoking this
method and it can be filled in the function only. #28940
- Remove the `RepoPath()`/`WikiPath()` functions to reduce the
possibility of mistakes.

---------

Co-authored-by: delvh <dev.lh@web.de>

modules/gitrepo/branch.go

@@ -0,0 +1,32 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package gitrepo
+
+import (
+	"context"
+
+	"code.gitea.io/gitea/modules/git"
+)
+
+// GetBranchesByPath returns a branch by its path
+// if limit = 0 it will not limit
+func GetBranchesByPath(ctx context.Context, repo Repository, skip, limit int) ([]*git.Branch, int, error) {
+	gitRepo, err := OpenRepository(ctx, repo)
+	if err != nil {
+		return nil, 0, err
+	}
+	defer gitRepo.Close()
+
+	return gitRepo.GetBranches(skip, limit)
+}
+
+func GetBranchCommitID(ctx context.Context, repo Repository, branch string) (string, error) {
+	gitRepo, err := OpenRepository(ctx, repo)
+	if err != nil {
+		return "", err
+	}
+	defer gitRepo.Close()
+
+	return gitRepo.GetBranchCommitID(branch)
+}

modules/gitrepo/gitrepo.go

@@ -0,0 +1,103 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package gitrepo
+
+import (
+	"context"
+	"io"
+	"path/filepath"
+	"strings"
+
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/setting"
+)
+
+type Repository interface {
+	GetName() string
+	GetOwnerName() string
+}
+
+func repoPath(repo Repository) string {
+	return filepath.Join(setting.RepoRootPath, strings.ToLower(repo.GetOwnerName()), strings.ToLower(repo.GetName())+".git")
+}
+
+func wikiPath(repo Repository) string {
+	return filepath.Join(setting.RepoRootPath, strings.ToLower(repo.GetOwnerName()), strings.ToLower(repo.GetName())+".wiki.git")
+}
+
+// OpenRepository opens the repository at the given relative path with the provided context.
+func OpenRepository(ctx context.Context, repo Repository) (*git.Repository, error) {
+	return git.OpenRepository(ctx, repoPath(repo))
+}
+
+func OpenWikiRepository(ctx context.Context, repo Repository) (*git.Repository, error) {
+	return git.OpenRepository(ctx, wikiPath(repo))
+}
+
+// contextKey is a value for use with context.WithValue.
+type contextKey struct {
+	name string
+}
+
+// RepositoryContextKey is a context key. It is used with context.Value() to get the current Repository for the context
+var RepositoryContextKey = &contextKey{"repository"}
+
+// RepositoryFromContext attempts to get the repository from the context
+func repositoryFromContext(ctx context.Context, repo Repository) *git.Repository {
+	value := ctx.Value(RepositoryContextKey)
+	if value == nil {
+		return nil
+	}
+
+	if gitRepo, ok := value.(*git.Repository); ok && gitRepo != nil {
+		if gitRepo.Path == repoPath(repo) {
+			return gitRepo
+		}
+	}
+
+	return nil
+}
+
+type nopCloser func()
+
+func (nopCloser) Close() error { return nil }
+
+// RepositoryFromContextOrOpen attempts to get the repository from the context or just opens it
+func RepositoryFromContextOrOpen(ctx context.Context, repo Repository) (*git.Repository, io.Closer, error) {
+	gitRepo := repositoryFromContext(ctx, repo)
+	if gitRepo != nil {
+		return gitRepo, nopCloser(nil), nil
+	}
+
+	gitRepo, err := OpenRepository(ctx, repo)
+	return gitRepo, gitRepo, err
+}
+
+// repositoryFromContextPath attempts to get the repository from the context
+func repositoryFromContextPath(ctx context.Context, path string) *git.Repository {
+	value := ctx.Value(RepositoryContextKey)
+	if value == nil {
+		return nil
+	}
+
+	if repo, ok := value.(*git.Repository); ok && repo != nil {
+		if repo.Path == path {
+			return repo
+		}
+	}
+
+	return nil
+}
+
+// RepositoryFromContextOrOpenPath attempts to get the repository from the context or just opens it
+// Deprecated: Use RepositoryFromContextOrOpen instead
+func RepositoryFromContextOrOpenPath(ctx context.Context, path string) (*git.Repository, io.Closer, error) {
+	gitRepo := repositoryFromContextPath(ctx, path)
+	if gitRepo != nil {
+		return gitRepo, nopCloser(nil), nil
+	}
+
+	gitRepo, err := git.OpenRepository(ctx, path)
+	return gitRepo, gitRepo, err
+}

modules/gitrepo/walk_gogit.go

@@ -0,0 +1,40 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build gogit
+
+package gitrepo
+
+import (
+	"context"
+
+	"github.com/go-git/go-git/v5/plumbing"
+)
+
+// WalkReferences walks all the references from the repository
+// refname is empty, ObjectTag or ObjectBranch. All other values should be treated as equivalent to empty.
+func WalkReferences(ctx context.Context, repo Repository, walkfn func(sha1, refname string) error) (int, error) {
+	gitRepo := repositoryFromContext(ctx, repo)
+	if gitRepo == nil {
+		var err error
+		gitRepo, err = OpenRepository(ctx, repo)
+		if err != nil {
+			return 0, err
+		}
+		defer gitRepo.Close()
+	}
+
+	i := 0
+	iter, err := gitRepo.GoGitRepo().References()
+	if err != nil {
+		return i, err
+	}
+	defer iter.Close()
+
+	err = iter.ForEach(func(ref *plumbing.Reference) error {
+		err := walkfn(ref.Hash().String(), string(ref.Name()))
+		i++
+		return err
+	})
+	return i, err
+}

modules/gitrepo/walk_nogogit.go

@@ -0,0 +1,17 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build !gogit
+
+package gitrepo
+
+import (
+	"context"
+
+	"code.gitea.io/gitea/modules/git"
+)
+
+// WalkReferences walks all the references from the repository
+func WalkReferences(ctx context.Context, repo Repository, walkfn func(sha1, refname string) error) (int, error) {
+	return git.WalkShowRef(ctx, repoPath(repo), nil, 0, 0, walkfn)
+}