Add apply-patch, basic revert and cherry-pick functionality (#17902)

This code adds a simple endpoint to apply patches to repositories and
branches on gitea. This is then used along with the conflicting checking
code in #18004 to provide a basic implementation of cherry-pick revert.

Now because the buttons necessary for cherry-pick and revert have 
required us to create a dropdown next to the Browse Source button
I've also implemented Create Branch and Create Tag operations.

Fix #3880 
Fix #17986 

Signed-off-by: Andrew Thornton <art27@cantab.net>

2 files changed, 319 insertions, 0 deletions

diff --git a/services/repository/files/cherry_pick.go b/services/repository/files/cherry_pick.go
new file mode 100644
index 0000000000..dc932b39c2
--- /dev/null
+++ b/services/repository/files/cherry_pick.go
@@ -0,0 +1,126 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package files
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"code.gitea.io/gitea/models"
+	repo_model "code.gitea.io/gitea/models/repo"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/services/pull"
+)
+
+// CherryPick cherrypicks or reverts a commit to the given repository
+func CherryPick(ctx context.Context, repo *repo_model.Repository, doer *user_model.User, revert bool, opts *ApplyDiffPatchOptions) (*structs.FileResponse, error) {
+	if err := opts.Validate(ctx, repo, doer); err != nil {
+		return nil, err
+	}
+	message := strings.TrimSpace(opts.Message)
+
+	author, committer := GetAuthorAndCommitterUsers(opts.Author, opts.Committer, doer)
+
+	t, err := NewTemporaryUploadRepository(ctx, repo)
+	if err != nil {
+		log.Error("%v", err)
+	}
+	defer t.Close()
+	if err := t.Clone(opts.OldBranch); err != nil {
+		return nil, err
+	}
+	if err := t.SetDefaultIndex(); err != nil {
+		return nil, err
+	}
+
+	// Get the commit of the original branch
+	commit, err := t.GetBranchCommit(opts.OldBranch)
+	if err != nil {
+		return nil, err // Couldn't get a commit for the branch
+	}
+
+	// Assigned LastCommitID in opts if it hasn't been set
+	if opts.LastCommitID == "" {
+		opts.LastCommitID = commit.ID.String()
+	} else {
+		lastCommitID, err := t.gitRepo.ConvertToSHA1(opts.LastCommitID)
+		if err != nil {
+			return nil, fmt.Errorf("CherryPick: Invalid last commit ID: %v", err)
+		}
+		opts.LastCommitID = lastCommitID.String()
+		if commit.ID.String() != opts.LastCommitID {
+			return nil, models.ErrCommitIDDoesNotMatch{
+				GivenCommitID:   opts.LastCommitID,
+				CurrentCommitID: opts.LastCommitID,
+			}
+		}
+	}
+
+	commit, err = t.GetCommit(strings.TrimSpace(opts.Content))
+	if err != nil {
+		return nil, err
+	}
+	parent, err := commit.ParentID(0)
+	if err != nil {
+		parent = git.MustIDFromString(git.EmptyTreeSHA)
+	}
+
+	base, right := parent.String(), commit.ID.String()
+
+	if revert {
+		right, base = base, right
+	}
+
+	description := fmt.Sprintf("CherryPick %s onto %s", right, opts.OldBranch)
+	conflict, _, err := pull.AttemptThreeWayMerge(ctx,
+		t.basePath, t.gitRepo, base, opts.LastCommitID, right, description)
+	if err != nil {
+		return nil, fmt.Errorf("failed to three-way merge %s onto %s: %v", right, opts.OldBranch, err)
+	}
+
+	if conflict {
+		return nil, fmt.Errorf("failed to merge due to conflicts")
+	}
+
+	treeHash, err := t.WriteTree()
+	if err != nil {
+		// likely non-sensical tree due to merge conflicts...
+		return nil, err
+	}
+
+	// Now commit the tree
+	var commitHash string
+	if opts.Dates != nil {
+		commitHash, err = t.CommitTreeWithDate(author, committer, treeHash, message, opts.Signoff, opts.Dates.Author, opts.Dates.Committer)
+	} else {
+		commitHash, err = t.CommitTree(author, committer, treeHash, message, opts.Signoff)
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	// Then push this tree to NewBranch
+	if err := t.Push(doer, commitHash, opts.NewBranch); err != nil {
+		return nil, err
+	}
+
+	commit, err = t.GetCommit(commitHash)
+	if err != nil {
+		return nil, err
+	}
+
+	fileCommitResponse, _ := GetFileCommitResponse(repo, commit) // ok if fails, then will be nil
+	verification := GetPayloadCommitVerification(commit)
+	fileResponse := &structs.FileResponse{
+		Commit:       fileCommitResponse,
+		Verification: verification,
+	}
+
+	return fileResponse, nil
+}
diff --git a/services/repository/files/patch.go b/services/repository/files/patch.go
new file mode 100644
index 0000000000..09a8b3ea0c
--- /dev/null
+++ b/services/repository/files/patch.go
@@ -0,0 +1,193 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package files
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"code.gitea.io/gitea/models"
+	repo_model "code.gitea.io/gitea/models/repo"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/structs"
+	asymkey_service "code.gitea.io/gitea/services/asymkey"
+)
+
+// ApplyDiffPatchOptions holds the repository diff patch update options
+type ApplyDiffPatchOptions struct {
+	LastCommitID string
+	OldBranch    string
+	NewBranch    string
+	Message      string
+	Content      string
+	SHA          string
+	Author       *IdentityOptions
+	Committer    *IdentityOptions
+	Dates        *CommitDateOptions
+	Signoff      bool
+}
+
+// Validate validates the provided options
+func (opts *ApplyDiffPatchOptions) Validate(ctx context.Context, repo *repo_model.Repository, doer *user_model.User) error {
+	// If no branch name is set, assume master
+	if opts.OldBranch == "" {
+		opts.OldBranch = repo.DefaultBranch
+	}
+	if opts.NewBranch == "" {
+		opts.NewBranch = opts.OldBranch
+	}
+
+	gitRepo, closer, err := git.RepositoryFromContextOrOpen(ctx, repo.RepoPath())
+	if err != nil {
+		return err
+	}
+	defer closer.Close()
+
+	// oldBranch must exist for this operation
+	if _, err := gitRepo.GetBranch(opts.OldBranch); err != nil {
+		return err
+	}
+	// A NewBranch can be specified for the patch to be applied to.
+	// Check to make sure the branch does not already exist, otherwise we can't proceed.
+	// If we aren't branching to a new branch, make sure user can commit to the given branch
+	if opts.NewBranch != opts.OldBranch {
+		existingBranch, err := gitRepo.GetBranch(opts.NewBranch)
+		if existingBranch != nil {
+			return models.ErrBranchAlreadyExists{
+				BranchName: opts.NewBranch,
+			}
+		}
+		if err != nil && !git.IsErrBranchNotExist(err) {
+			return err
+		}
+	} else {
+		protectedBranch, err := models.GetProtectedBranchBy(repo.ID, opts.OldBranch)
+		if err != nil {
+			return err
+		}
+		if protectedBranch != nil && !protectedBranch.CanUserPush(doer.ID) {
+			return models.ErrUserCannotCommit{
+				UserName: doer.LowerName,
+			}
+		}
+		if protectedBranch != nil && protectedBranch.RequireSignedCommits {
+			_, _, _, err := asymkey_service.SignCRUDAction(ctx, repo.RepoPath(), doer, repo.RepoPath(), opts.OldBranch)
+			if err != nil {
+				if !asymkey_service.IsErrWontSign(err) {
+					return err
+				}
+				return models.ErrUserCannotCommit{
+					UserName: doer.LowerName,
+				}
+			}
+		}
+	}
+	return nil
+}
+
+// ApplyDiffPatch applies a patch to the given repository
+func ApplyDiffPatch(ctx context.Context, repo *repo_model.Repository, doer *user_model.User, opts *ApplyDiffPatchOptions) (*structs.FileResponse, error) {
+	if err := opts.Validate(ctx, repo, doer); err != nil {
+		return nil, err
+	}
+
+	message := strings.TrimSpace(opts.Message)
+
+	author, committer := GetAuthorAndCommitterUsers(opts.Author, opts.Committer, doer)
+
+	t, err := NewTemporaryUploadRepository(ctx, repo)
+	if err != nil {
+		log.Error("%v", err)
+	}
+	defer t.Close()
+	if err := t.Clone(opts.OldBranch); err != nil {
+		return nil, err
+	}
+	if err := t.SetDefaultIndex(); err != nil {
+		return nil, err
+	}
+
+	// Get the commit of the original branch
+	commit, err := t.GetBranchCommit(opts.OldBranch)
+	if err != nil {
+		return nil, err // Couldn't get a commit for the branch
+	}
+
+	// Assigned LastCommitID in opts if it hasn't been set
+	if opts.LastCommitID == "" {
+		opts.LastCommitID = commit.ID.String()
+	} else {
+		lastCommitID, err := t.gitRepo.ConvertToSHA1(opts.LastCommitID)
+		if err != nil {
+			return nil, fmt.Errorf("ApplyPatch: Invalid last commit ID: %v", err)
+		}
+		opts.LastCommitID = lastCommitID.String()
+		if commit.ID.String() != opts.LastCommitID {
+			return nil, models.ErrCommitIDDoesNotMatch{
+				GivenCommitID:   opts.LastCommitID,
+				CurrentCommitID: opts.LastCommitID,
+			}
+		}
+	}
+
+	stdout := &strings.Builder{}
+	stderr := &strings.Builder{}
+
+	args := []string{"apply", "--index", "--recount", "--cached", "--ignore-whitespace", "--whitespace=fix", "--binary"}
+
+	if git.CheckGitVersionAtLeast("2.32") == nil {
+		args = append(args, "-3")
+	}
+
+	cmd := git.NewCommand(ctx, args...)
+	if err := cmd.RunWithContext(&git.RunContext{
+		Timeout: -1,
+		Dir:     t.basePath,
+		Stdout:  stdout,
+		Stderr:  stderr,
+		Stdin:   strings.NewReader(opts.Content),
+	}); err != nil {
+		return nil, fmt.Errorf("Error: Stdout: %s\nStderr: %s\nErr: %v", stdout.String(), stderr.String(), err)
+	}
+
+	// Now write the tree
+	treeHash, err := t.WriteTree()
+	if err != nil {
+		return nil, err
+	}
+
+	// Now commit the tree
+	var commitHash string
+	if opts.Dates != nil {
+		commitHash, err = t.CommitTreeWithDate(author, committer, treeHash, message, opts.Signoff, opts.Dates.Author, opts.Dates.Committer)
+	} else {
+		commitHash, err = t.CommitTree(author, committer, treeHash, message, opts.Signoff)
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	// Then push this tree to NewBranch
+	if err := t.Push(doer, commitHash, opts.NewBranch); err != nil {
+		return nil, err
+	}
+
+	commit, err = t.GetCommit(commitHash)
+	if err != nil {
+		return nil, err
+	}
+
+	fileCommitResponse, _ := GetFileCommitResponse(repo, commit) // ok if fails, then will be nil
+	verification := GetPayloadCommitVerification(commit)
+	fileResponse := &structs.FileResponse{
+		Commit:       fileCommitResponse,
+		Verification: verification,
+	}
+
+	return fileResponse, nil
+}