Refactor and tidy-up the merge/update branch code (#22568)

The merge and update branch code was previously a little tangled and had
some very long functions. The functions were not very clear in their
reasoning and there were deficiencies in their logging and at least one
bug in the handling of LFS for update by rebase.

This PR substantially refactors this code and splits things out to into
separate functions. It also attempts to tidy up the calls by wrapping
things in "context"s. There are also attempts to improve logging when
there are errors.

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

---------

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: delvh <dev.lh@web.de>

1 files changed, 94 insertions, 100 deletions

diff --git a/services/pull/temp_repo.go b/services/pull/temp_repo.go
index 2bef671555..1464707806 100644
--- a/services/pull/temp_repo.go
+++ b/services/pull/temp_repo.go
@@ -19,49 +19,85 @@ import (
 	repo_module "code.gitea.io/gitea/modules/repository"
 )
 
-// createTemporaryRepo creates a temporary repo with "base" for pr.BaseBranch and "tracking" for  pr.HeadBranch
+// Temporary repos created here use standard branch names to help simplify
+// merging code
+const (
+	baseBranch     = "base"     // equivalent to pr.BaseBranch
+	trackingBranch = "tracking" // equivalent to pr.HeadBranch
+	stagingBranch  = "staging"  // this is used for a working branch
+)
+
+type prContext struct {
+	context.Context
+	tmpBasePath string
+	pr          *issues_model.PullRequest
+	outbuf      *strings.Builder // we keep these around to help reduce needless buffer recreation,
+	errbuf      *strings.Builder // any use should be preceded by a Reset and preferably after use
+}
+
+func (ctx *prContext) RunOpts() *git.RunOpts {
+	ctx.outbuf.Reset()
+	ctx.errbuf.Reset()
+	return &git.RunOpts{
+		Dir:    ctx.tmpBasePath,
+		Stdout: ctx.outbuf,
+		Stderr: ctx.errbuf,
+	}
+}
+
+// createTemporaryRepoForPR creates a temporary repo with "base" for pr.BaseBranch and "tracking" for  pr.HeadBranch
 // it also create a second base branch called "original_base"
-func createTemporaryRepo(ctx context.Context, pr *issues_model.PullRequest) (string, error) {
+func createTemporaryRepoForPR(ctx context.Context, pr *issues_model.PullRequest) (prCtx *prContext, cancel context.CancelFunc, err error) {
 	if err := pr.LoadHeadRepo(ctx); err != nil {
-		log.Error("LoadHeadRepo: %v", err)
-		return "", fmt.Errorf("LoadHeadRepo: %w", err)
+		log.Error("%-v LoadHeadRepo: %v", pr, err)
+		return nil, nil, fmt.Errorf("%v LoadHeadRepo: %w", pr, err)
 	} else if pr.HeadRepo == nil {
-		log.Error("Pr %d HeadRepo %d does not exist", pr.ID, pr.HeadRepoID)
-		return "", &repo_model.ErrRepoNotExist{
+		log.Error("%-v HeadRepo %d does not exist", pr, pr.HeadRepoID)
+		return nil, nil, &repo_model.ErrRepoNotExist{
 			ID: pr.HeadRepoID,
 		}
 	} else if err := pr.LoadBaseRepo(ctx); err != nil {
-		log.Error("LoadBaseRepo: %v", err)
-		return "", fmt.Errorf("LoadBaseRepo: %w", err)
+		log.Error("%-v LoadBaseRepo: %v", pr, err)
+		return nil, nil, fmt.Errorf("%v LoadBaseRepo: %w", pr, err)
 	} else if pr.BaseRepo == nil {
-		log.Error("Pr %d BaseRepo %d does not exist", pr.ID, pr.BaseRepoID)
-		return "", &repo_model.ErrRepoNotExist{
+		log.Error("%-v BaseRepo %d does not exist", pr, pr.BaseRepoID)
+		return nil, nil, &repo_model.ErrRepoNotExist{
 			ID: pr.BaseRepoID,
 		}
 	} else if err := pr.HeadRepo.LoadOwner(ctx); err != nil {
-		log.Error("HeadRepo.LoadOwner: %v", err)
-		return "", fmt.Errorf("HeadRepo.LoadOwner: %w", err)
+		log.Error("%-v HeadRepo.LoadOwner: %v", pr, err)
+		return nil, nil, fmt.Errorf("%v HeadRepo.LoadOwner: %w", pr, err)
 	} else if err := pr.BaseRepo.LoadOwner(ctx); err != nil {
-		log.Error("BaseRepo.LoadOwner: %v", err)
-		return "", fmt.Errorf("BaseRepo.LoadOwner: %w", err)
+		log.Error("%-v BaseRepo.LoadOwner: %v", pr, err)
+		return nil, nil, fmt.Errorf("%v BaseRepo.LoadOwner: %w", pr, err)
 	}
 
 	// Clone base repo.
 	tmpBasePath, err := repo_module.CreateTemporaryPath("pull")
 	if err != nil {
-		log.Error("CreateTemporaryPath: %v", err)
-		return "", err
+		log.Error("CreateTemporaryPath[%-v]: %v", pr, err)
+		return nil, nil, err
+	}
+	prCtx = &prContext{
+		Context:     ctx,
+		tmpBasePath: tmpBasePath,
+		pr:          pr,
+		outbuf:      &strings.Builder{},
+		errbuf:      &strings.Builder{},
+	}
+	cancel = func() {
+		if err := repo_module.RemoveTemporaryPath(tmpBasePath); err != nil {
+			log.Error("Error whilst removing removing temporary repo for %-v: %v", pr, err)
+		}
 	}
 
 	baseRepoPath := pr.BaseRepo.RepoPath()
 	headRepoPath := pr.HeadRepo.RepoPath()
 
 	if err := git.InitRepository(ctx, tmpBasePath, false); err != nil {
-		log.Error("git init tmpBasePath: %v", err)
-		if err := repo_module.RemoveTemporaryPath(tmpBasePath); err != nil {
-			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
-		}
-		return "", err
+		log.Error("Unable to init tmpBasePath for %-v: %v", pr, err)
+		cancel()
+		return nil, nil, err
 	}
 
 	remoteRepoName := "head_repo"
@@ -73,99 +109,63 @@ func createTemporaryRepo(ctx context.Context, pr *issues_model.PullRequest) (str
 		fetchArgs = append(fetchArgs, "--no-write-commit-graph")
 	}
 
-	// Add head repo remote.
-	addCacheRepo := func(staging, cache string) error {
-		p := filepath.Join(staging, ".git", "objects", "info", "alternates")
+	// addCacheRepo adds git alternatives for the cacheRepoPath in the repoPath
+	addCacheRepo := func(repoPath, cacheRepoPath string) error {
+		p := filepath.Join(repoPath, ".git", "objects", "info", "alternates")
 		f, err := os.OpenFile(p, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o600)
 		if err != nil {
-			log.Error("Could not create .git/objects/info/alternates file in %s: %v", staging, err)
+			log.Error("Could not create .git/objects/info/alternates file in %s: %v", repoPath, err)
 			return err
 		}
 		defer f.Close()
-		data := filepath.Join(cache, "objects")
+		data := filepath.Join(cacheRepoPath, "objects")
 		if _, err := fmt.Fprintln(f, data); err != nil {
-			log.Error("Could not write to .git/objects/info/alternates file in %s: %v", staging, err)
+			log.Error("Could not write to .git/objects/info/alternates file in %s: %v", repoPath, err)
 			return err
 		}
 		return nil
 	}
 
+	// Add head repo remote.
 	if err := addCacheRepo(tmpBasePath, baseRepoPath); err != nil {
-		log.Error("Unable to add base repository to temporary repo [%s -> %s]: %v", pr.BaseRepo.FullName(), tmpBasePath, err)
-		if err := repo_module.RemoveTemporaryPath(tmpBasePath); err != nil {
-			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
-		}
-		return "", fmt.Errorf("Unable to add base repository to temporary repo [%s -> tmpBasePath]: %w", pr.BaseRepo.FullName(), err)
+		log.Error("%-v Unable to add base repository to temporary repo [%s -> %s]: %v", pr, pr.BaseRepo.FullName(), tmpBasePath, err)
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to add base repository to temporary repo [%s -> tmpBasePath]: %w", pr.BaseRepo.FullName(), err)
 	}
 
-	var outbuf, errbuf strings.Builder
 	if err := git.NewCommand(ctx, "remote", "add", "-t").AddDynamicArguments(pr.BaseBranch).AddArguments("-m").AddDynamicArguments(pr.BaseBranch).AddDynamicArguments("origin", baseRepoPath).
-		Run(&git.RunOpts{
-			Dir:    tmpBasePath,
-			Stdout: &outbuf,
-			Stderr: &errbuf,
-		}); err != nil {
-		log.Error("Unable to add base repository as origin [%s -> %s]: %v\n%s\n%s", pr.BaseRepo.FullName(), tmpBasePath, err, outbuf.String(), errbuf.String())
-		if err := repo_module.RemoveTemporaryPath(tmpBasePath); err != nil {
-			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
-		}
-		return "", fmt.Errorf("Unable to add base repository as origin [%s -> tmpBasePath]: %w\n%s\n%s", pr.BaseRepo.FullName(), err, outbuf.String(), errbuf.String())
+		Run(prCtx.RunOpts()); err != nil {
+		log.Error("%-v Unable to add base repository as origin [%s -> %s]: %v\n%s\n%s", pr, pr.BaseRepo.FullName(), tmpBasePath, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to add base repository as origin [%s -> tmpBasePath]: %w\n%s\n%s", pr.BaseRepo.FullName(), err, prCtx.outbuf.String(), prCtx.errbuf.String())
 	}
-	outbuf.Reset()
-	errbuf.Reset()
 
 	if err := git.NewCommand(ctx, "fetch", "origin").AddArguments(fetchArgs...).AddDashesAndList(pr.BaseBranch+":"+baseBranch, pr.BaseBranch+":original_"+baseBranch).
-		Run(&git.RunOpts{
-			Dir:    tmpBasePath,
-			Stdout: &outbuf,
-			Stderr: &errbuf,
-		}); err != nil {
-		log.Error("Unable to fetch origin base branch [%s:%s -> base, original_base in %s]: %v:\n%s\n%s", pr.BaseRepo.FullName(), pr.BaseBranch, tmpBasePath, err, outbuf.String(), errbuf.String())
-		if err := repo_module.RemoveTemporaryPath(tmpBasePath); err != nil {
-			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
-		}
-		return "", fmt.Errorf("Unable to fetch origin base branch [%s:%s -> base, original_base in tmpBasePath]: %w\n%s\n%s", pr.BaseRepo.FullName(), pr.BaseBranch, err, outbuf.String(), errbuf.String())
+		Run(prCtx.RunOpts()); err != nil {
+		log.Error("%-v Unable to fetch origin base branch [%s:%s -> base, original_base in %s]: %v:\n%s\n%s", pr, pr.BaseRepo.FullName(), pr.BaseBranch, tmpBasePath, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to fetch origin base branch [%s:%s -> base, original_base in tmpBasePath]: %w\n%s\n%s", pr.BaseRepo.FullName(), pr.BaseBranch, err, prCtx.outbuf.String(), prCtx.errbuf.String())
 	}
-	outbuf.Reset()
-	errbuf.Reset()
 
 	if err := git.NewCommand(ctx, "symbolic-ref").AddDynamicArguments("HEAD", git.BranchPrefix+baseBranch).
-		Run(&git.RunOpts{
-			Dir:    tmpBasePath,
-			Stdout: &outbuf,
-			Stderr: &errbuf,
-		}); err != nil {
-		log.Error("Unable to set HEAD as base branch [%s]: %v\n%s\n%s", tmpBasePath, err, outbuf.String(), errbuf.String())
-		if err := repo_module.RemoveTemporaryPath(tmpBasePath); err != nil {
-			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
-		}
-		return "", fmt.Errorf("Unable to set HEAD as base branch [tmpBasePath]: %w\n%s\n%s", err, outbuf.String(), errbuf.String())
+		Run(prCtx.RunOpts()); err != nil {
+		log.Error("%-v Unable to set HEAD as base branch in [%s]: %v\n%s\n%s", pr, tmpBasePath, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to set HEAD as base branch in tmpBasePath: %w\n%s\n%s", err, prCtx.outbuf.String(), prCtx.errbuf.String())
 	}
-	outbuf.Reset()
-	errbuf.Reset()
 
 	if err := addCacheRepo(tmpBasePath, headRepoPath); err != nil {
-		log.Error("Unable to add head repository to temporary repo [%s -> %s]: %v", pr.HeadRepo.FullName(), tmpBasePath, err)
-		if err := repo_module.RemoveTemporaryPath(tmpBasePath); err != nil {
-			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
-		}
-		return "", fmt.Errorf("Unable to head base repository to temporary repo [%s -> tmpBasePath]: %w", pr.HeadRepo.FullName(), err)
+		log.Error("%-v Unable to add head repository to temporary repo [%s -> %s]: %v", pr, pr.HeadRepo.FullName(), tmpBasePath, err)
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to add head base repository to temporary repo [%s -> tmpBasePath]: %w", pr.HeadRepo.FullName(), err)
 	}
 
 	if err := git.NewCommand(ctx, "remote", "add").AddDynamicArguments(remoteRepoName, headRepoPath).
-		Run(&git.RunOpts{
-			Dir:    tmpBasePath,
-			Stdout: &outbuf,
-			Stderr: &errbuf,
-		}); err != nil {
-		log.Error("Unable to add head repository as head_repo [%s -> %s]: %v\n%s\n%s", pr.HeadRepo.FullName(), tmpBasePath, err, outbuf.String(), errbuf.String())
-		if err := repo_module.RemoveTemporaryPath(tmpBasePath); err != nil {
-			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
-		}
-		return "", fmt.Errorf("Unable to add head repository as head_repo [%s -> tmpBasePath]: %w\n%s\n%s", pr.HeadRepo.FullName(), err, outbuf.String(), errbuf.String())
+		Run(prCtx.RunOpts()); err != nil {
+		log.Error("%-v Unable to add head repository as head_repo [%s -> %s]: %v\n%s\n%s", pr, pr.HeadRepo.FullName(), tmpBasePath, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+		cancel()
+		return nil, nil, fmt.Errorf("Unable to add head repository as head_repo [%s -> tmpBasePath]: %w\n%s\n%s", pr.HeadRepo.FullName(), err, prCtx.outbuf.String(), prCtx.errbuf.String())
 	}
-	outbuf.Reset()
-	errbuf.Reset()
 
 	trackingBranch := "tracking"
 	// Fetch head branch
@@ -178,24 +178,18 @@ func createTemporaryRepo(ctx context.Context, pr *issues_model.PullRequest) (str
 		headBranch = pr.GetGitRefName()
 	}
 	if err := git.NewCommand(ctx, "fetch").AddArguments(fetchArgs...).AddDynamicArguments(remoteRepoName, headBranch+":"+trackingBranch).
-		Run(&git.RunOpts{
-			Dir:    tmpBasePath,
-			Stdout: &outbuf,
-			Stderr: &errbuf,
-		}); err != nil {
-		if err := repo_module.RemoveTemporaryPath(tmpBasePath); err != nil {
-			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
-		}
+		Run(prCtx.RunOpts()); err != nil {
+		cancel()
 		if !git.IsBranchExist(ctx, pr.HeadRepo.RepoPath(), pr.HeadBranch) {
-			return "", models.ErrBranchDoesNotExist{
+			return nil, nil, models.ErrBranchDoesNotExist{
 				BranchName: pr.HeadBranch,
 			}
 		}
-		log.Error("Unable to fetch head_repo head branch [%s:%s -> tracking in %s]: %v:\n%s\n%s", pr.HeadRepo.FullName(), pr.HeadBranch, tmpBasePath, err, outbuf.String(), errbuf.String())
-		return "", fmt.Errorf("Unable to fetch head_repo head branch [%s:%s -> tracking in tmpBasePath]: %w\n%s\n%s", pr.HeadRepo.FullName(), headBranch, err, outbuf.String(), errbuf.String())
+		log.Error("%-v Unable to fetch head_repo head branch [%s:%s -> tracking in %s]: %v:\n%s\n%s", pr, pr.HeadRepo.FullName(), pr.HeadBranch, tmpBasePath, err, prCtx.outbuf.String(), prCtx.errbuf.String())
+		return nil, nil, fmt.Errorf("Unable to fetch head_repo head branch [%s:%s -> tracking in tmpBasePath]: %w\n%s\n%s", pr.HeadRepo.FullName(), headBranch, err, prCtx.outbuf.String(), prCtx.errbuf.String())
 	}
-	outbuf.Reset()
-	errbuf.Reset()
+	prCtx.outbuf.Reset()
+	prCtx.errbuf.Reset()
 
-	return tmpBasePath, nil
+	return prCtx, cancel, nil
 }