1 files changed, 297 insertions, 0 deletions

diff --git a/services/pull/merge_prepare.go b/services/pull/merge_prepare.go
new file mode 100644
index 000000000..2ba821961
--- /dev/null
+++ b/services/pull/merge_prepare.go
@@ -0,0 +1,297 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package pull
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"code.gitea.io/gitea/models"
+	issues_model "code.gitea.io/gitea/models/issues"
+	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"
+	asymkey_service "code.gitea.io/gitea/services/asymkey"
+)
+
+type mergeContext struct {
+	*prContext
+	doer      *user_model.User
+	sig       *git.Signature
+	committer *git.Signature
+	signArg   git.TrustedCmdArgs
+	env       []string
+}
+
+func (ctx *mergeContext) RunOpts() *git.RunOpts {
+	ctx.outbuf.Reset()
+	ctx.errbuf.Reset()
+	return &git.RunOpts{
+		Env:    ctx.env,
+		Dir:    ctx.tmpBasePath,
+		Stdout: ctx.outbuf,
+		Stderr: ctx.errbuf,
+	}
+}
+
+func createTemporaryRepoForMerge(ctx context.Context, pr *issues_model.PullRequest, doer *user_model.User, expectedHeadCommitID string) (mergeCtx *mergeContext, cancel context.CancelFunc, err error) {
+	// Clone base repo.
+	prCtx, cancel, err := createTemporaryRepoForPR(ctx, pr)
+	if err != nil {
+		log.Error("createTemporaryRepoForPR: %v", err)
+		return nil, cancel, err
+	}
+
+	mergeCtx = &mergeContext{
+		prContext: prCtx,
+		doer:      doer,
+	}
+
+	if expectedHeadCommitID != "" {
+		trackingCommitID, _, err := git.NewCommand(ctx, "show-ref", "--hash").AddDynamicArguments(git.BranchPrefix + trackingBranch).RunStdString(&git.RunOpts{Dir: mergeCtx.tmpBasePath})
+		if err != nil {
+			defer cancel()
+			log.Error("failed to get sha of head branch in %-v: show-ref[%s] --hash refs/heads/tracking: %v", mergeCtx.pr, mergeCtx.tmpBasePath, err)
+			return nil, nil, fmt.Errorf("unable to get sha of head branch in %v %w", pr, err)
+		}
+		if strings.TrimSpace(trackingCommitID) != expectedHeadCommitID {
+			defer cancel()
+			return nil, nil, models.ErrSHADoesNotMatch{
+				GivenSHA:   expectedHeadCommitID,
+				CurrentSHA: trackingCommitID,
+			}
+		}
+	}
+
+	mergeCtx.outbuf.Reset()
+	mergeCtx.errbuf.Reset()
+	if err := prepareTemporaryRepoForMerge(mergeCtx); err != nil {
+		defer cancel()
+		return nil, nil, err
+	}
+
+	mergeCtx.sig = doer.NewGitSig()
+	mergeCtx.committer = mergeCtx.sig
+
+	// Determine if we should sign
+	sign, keyID, signer, _ := asymkey_service.SignMerge(ctx, mergeCtx.pr, mergeCtx.doer, mergeCtx.tmpBasePath, "HEAD", trackingBranch)
+	if sign {
+		mergeCtx.signArg = git.ToTrustedCmdArgs([]string{"-S" + keyID})
+		if pr.BaseRepo.GetTrustModel() == repo_model.CommitterTrustModel || pr.BaseRepo.GetTrustModel() == repo_model.CollaboratorCommitterTrustModel {
+			mergeCtx.committer = signer
+		}
+	} else {
+		mergeCtx.signArg = git.ToTrustedCmdArgs([]string{"--no-gpg-sign"})
+	}
+
+	commitTimeStr := time.Now().Format(time.RFC3339)
+
+	// Because this may call hooks we should pass in the environment
+	mergeCtx.env = append(os.Environ(),
+		"GIT_AUTHOR_NAME="+mergeCtx.sig.Name,
+		"GIT_AUTHOR_EMAIL="+mergeCtx.sig.Email,
+		"GIT_AUTHOR_DATE="+commitTimeStr,
+		"GIT_COMMITTER_NAME="+mergeCtx.committer.Name,
+		"GIT_COMMITTER_EMAIL="+mergeCtx.committer.Email,
+		"GIT_COMMITTER_DATE="+commitTimeStr,
+	)
+
+	return mergeCtx, cancel, nil
+}
+
+// prepareTemporaryRepoForMerge takes a repository that has been created using createTemporaryRepo
+// it then sets up the sparse-checkout and other things
+func prepareTemporaryRepoForMerge(ctx *mergeContext) error {
+	infoPath := filepath.Join(ctx.tmpBasePath, ".git", "info")
+	if err := os.MkdirAll(infoPath, 0o700); err != nil {
+		log.Error("%-v Unable to create .git/info in %s: %v", ctx.pr, ctx.tmpBasePath, err)
+		return fmt.Errorf("Unable to create .git/info in tmpBasePath: %w", err)
+	}
+
+	// Enable sparse-checkout
+	// Here we use the .git/info/sparse-checkout file as described in the git documentation
+	sparseCheckoutListFile, err := os.OpenFile(filepath.Join(infoPath, "sparse-checkout"), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o600)
+	if err != nil {
+		log.Error("%-v Unable to write .git/info/sparse-checkout file in %s: %v", ctx.pr, ctx.tmpBasePath, err)
+		return fmt.Errorf("Unable to write .git/info/sparse-checkout file in tmpBasePath: %w", err)
+	}
+	defer sparseCheckoutListFile.Close() // we will close it earlier but we need to ensure it is closed if there is an error
+
+	if err := getDiffTree(ctx, ctx.tmpBasePath, baseBranch, trackingBranch, sparseCheckoutListFile); err != nil {
+		log.Error("%-v getDiffTree(%s, %s, %s): %v", ctx.pr, ctx.tmpBasePath, baseBranch, trackingBranch, err)
+		return fmt.Errorf("getDiffTree: %w", err)
+	}
+
+	if err := sparseCheckoutListFile.Close(); err != nil {
+		log.Error("%-v Unable to close .git/info/sparse-checkout file in %s: %v", ctx.pr, ctx.tmpBasePath, err)
+		return fmt.Errorf("Unable to close .git/info/sparse-checkout file in tmpBasePath: %w", err)
+	}
+
+	gitConfigCommand := func() *git.Command {
+		return git.NewCommand(ctx, "config", "--local")
+	}
+
+	setConfig := func(key, value string) error {
+		if err := gitConfigCommand().AddArguments(git.ToTrustedCmdArgs([]string{key, value})...).
+			Run(ctx.RunOpts()); err != nil {
+			if value == "" {
+				value = "<>"
+			}
+			log.Error("git config [%s -> %s ]: %v\n%s\n%s", key, value, err, ctx.outbuf.String(), ctx.errbuf.String())
+			return fmt.Errorf("git config [%s -> %s ]: %w\n%s\n%s", key, value, err, ctx.outbuf.String(), ctx.errbuf.String())
+		}
+		ctx.outbuf.Reset()
+		ctx.errbuf.Reset()
+
+		return nil
+	}
+
+	// Switch off LFS process (set required, clean and smudge here also)
+	if err := setConfig("filter.lfs.process", ""); err != nil {
+		return err
+	}
+
+	if err := setConfig("filter.lfs.required", "false"); err != nil {
+		return err
+	}
+
+	if err := setConfig("filter.lfs.clean", ""); err != nil {
+		return err
+	}
+
+	if err := setConfig("filter.lfs.smudge", ""); err != nil {
+		return err
+	}
+
+	if err := setConfig("core.sparseCheckout", "true"); err != nil {
+		return err
+	}
+
+	// Read base branch index
+	if err := git.NewCommand(ctx, "read-tree", "HEAD").
+		Run(ctx.RunOpts()); err != nil {
+		log.Error("git read-tree HEAD: %v\n%s\n%s", err, ctx.outbuf.String(), ctx.errbuf.String())
+		return fmt.Errorf("Unable to read base branch in to the index: %w\n%s\n%s", err, ctx.outbuf.String(), ctx.errbuf.String())
+	}
+	ctx.outbuf.Reset()
+	ctx.errbuf.Reset()
+
+	return nil
+}
+
+// getDiffTree returns a string containing all the files that were changed between headBranch and baseBranch
+// the filenames are escaped so as to fit the format required for .git/info/sparse-checkout
+func getDiffTree(ctx context.Context, repoPath, baseBranch, headBranch string, out io.Writer) error {
+	diffOutReader, diffOutWriter, err := os.Pipe()
+	if err != nil {
+		log.Error("Unable to create os.Pipe for %s", repoPath)
+		return err
+	}
+	defer func() {
+		_ = diffOutReader.Close()
+		_ = diffOutWriter.Close()
+	}()
+
+	scanNullTerminatedStrings := func(data []byte, atEOF bool) (advance int, token []byte, err error) {
+		if atEOF && len(data) == 0 {
+			return 0, nil, nil
+		}
+		if i := bytes.IndexByte(data, '\x00'); i >= 0 {
+			return i + 1, data[0:i], nil
+		}
+		if atEOF {
+			return len(data), data, nil
+		}
+		return 0, nil, nil
+	}
+
+	err = git.NewCommand(ctx, "diff-tree", "--no-commit-id", "--name-only", "-r", "-r", "-z", "--root").AddDynamicArguments(baseBranch, headBranch).
+		Run(&git.RunOpts{
+			Dir:    repoPath,
+			Stdout: diffOutWriter,
+			PipelineFunc: func(ctx context.Context, cancel context.CancelFunc) error {
+				// Close the writer end of the pipe to begin processing
+				_ = diffOutWriter.Close()
+				defer func() {
+					// Close the reader on return to terminate the git command if necessary
+					_ = diffOutReader.Close()
+				}()
+
+				// Now scan the output from the command
+				scanner := bufio.NewScanner(diffOutReader)
+				scanner.Split(scanNullTerminatedStrings)
+				for scanner.Scan() {
+					filepath := scanner.Text()
+					// escape '*', '?', '[', spaces and '!' prefix
+					filepath = escapedSymbols.ReplaceAllString(filepath, `\$1`)
+					// no necessary to escape the first '#' symbol because the first symbol is '/'
+					fmt.Fprintf(out, "/%s\n", filepath)
+				}
+				return scanner.Err()
+			},
+		})
+	return err
+}
+
+// rebaseTrackingOnToBase checks out the tracking branch as staging and rebases it on to the base branch
+// if there is a conflict it will return a models.ErrRebaseConflicts
+func rebaseTrackingOnToBase(ctx *mergeContext, mergeStyle repo_model.MergeStyle) error {
+	// Checkout head branch
+	if err := git.NewCommand(ctx, "checkout", "-b").AddDynamicArguments(stagingBranch, trackingBranch).
+		Run(ctx.RunOpts()); err != nil {
+		return fmt.Errorf("unable to git checkout tracking as staging in temp repo for %v: %w\n%s\n%s", ctx.pr, err, ctx.outbuf.String(), ctx.errbuf.String())
+	}
+	ctx.outbuf.Reset()
+	ctx.errbuf.Reset()
+
+	// Rebase before merging
+	if err := git.NewCommand(ctx, "rebase").AddDynamicArguments(baseBranch).
+		Run(ctx.RunOpts()); err != nil {
+		// Rebase will leave a REBASE_HEAD file in .git if there is a conflict
+		if _, statErr := os.Stat(filepath.Join(ctx.tmpBasePath, ".git", "REBASE_HEAD")); statErr == nil {
+			var commitSha string
+			ok := false
+			failingCommitPaths := []string{
+				filepath.Join(ctx.tmpBasePath, ".git", "rebase-apply", "original-commit"), // Git < 2.26
+				filepath.Join(ctx.tmpBasePath, ".git", "rebase-merge", "stopped-sha"),     // Git >= 2.26
+			}
+			for _, failingCommitPath := range failingCommitPaths {
+				if _, statErr := os.Stat(failingCommitPath); statErr == nil {
+					commitShaBytes, readErr := os.ReadFile(failingCommitPath)
+					if readErr != nil {
+						// Abandon this attempt to handle the error
+						return fmt.Errorf("unable to git rebase staging on to base in temp repo for %v: %w\n%s\n%s", ctx.pr, err, ctx.outbuf.String(), ctx.errbuf.String())
+					}
+					commitSha = strings.TrimSpace(string(commitShaBytes))
+					ok = true
+					break
+				}
+			}
+			if !ok {
+				log.Error("Unable to determine failing commit sha for failing rebase in temp repo for %-v. Cannot cast as models.ErrRebaseConflicts.", ctx.pr)
+				return fmt.Errorf("unable to git rebase staging on to base in temp repo for %v: %w\n%s\n%s", ctx.pr, err, ctx.outbuf.String(), ctx.errbuf.String())
+			}
+			log.Debug("Conflict when rebasing staging on to base in %-v at %s: %v\n%s\n%s", ctx.pr, commitSha, err, ctx.outbuf.String(), ctx.errbuf.String())
+			return models.ErrRebaseConflicts{
+				CommitSHA: commitSha,
+				Style:     mergeStyle,
+				StdOut:    ctx.outbuf.String(),
+				StdErr:    ctx.errbuf.String(),
+				Err:       err,
+			}
+		}
+		return fmt.Errorf("unable to git rebase staging on to base in temp repo for %v: %w\n%s\n%s", ctx.pr, err, ctx.outbuf.String(), ctx.errbuf.String())
+	}
+	ctx.outbuf.Reset()
+	ctx.errbuf.Reset()
+	return nil
+}