Fix pull request update showing too many commits with multiple branches (#22856)

When the base repository contains multiple branches with the same
commits as the base branch, pull requests can show a long list of
commits already in the base branch as having been added.

What this is supposed to do is exclude commits already in the base
branch. But the mechansim to do so assumed a commit only exists in a
single branch. Now use `git rev-list A B --not branchName` instead of
filtering commits afterwards.

The logic to detect if there was a force push also was wrong for
multiple branches. If the old commit existed in any branch in the base
repository it would assume there was no force push. Instead check if the
old commit is an ancestor of the new commit.

2 files changed, 15 insertions, 81 deletions

diff --git a/services/pull/comment.go b/services/pull/comment.go
index 068aca6cd..933ad09a8 100644
--- a/services/pull/comment.go
+++ b/services/pull/comment.go
@@ -14,58 +14,6 @@ import (
 	issue_service "code.gitea.io/gitea/services/issue"
 )
 
-type commitBranchCheckItem struct {
-	Commit  *git.Commit
-	Checked bool
-}
-
-func commitBranchCheck(gitRepo *git.Repository, startCommit *git.Commit, endCommitID, baseBranch string, commitList map[string]*commitBranchCheckItem) error {
-	if startCommit.ID.String() == endCommitID {
-		return nil
-	}
-
-	checkStack := make([]string, 0, 10)
-	checkStack = append(checkStack, startCommit.ID.String())
-
-	for len(checkStack) > 0 {
-		commitID := checkStack[0]
-		checkStack = checkStack[1:]
-
-		item, ok := commitList[commitID]
-		if !ok {
-			continue
-		}
-
-		if item.Commit.ID.String() == endCommitID {
-			continue
-		}
-
-		if err := item.Commit.LoadBranchName(); err != nil {
-			return err
-		}
-
-		if item.Commit.Branch == baseBranch {
-			continue
-		}
-
-		if item.Checked {
-			continue
-		}
-
-		item.Checked = true
-
-		parentNum := item.Commit.ParentCount()
-		for i := 0; i < parentNum; i++ {
-			parentCommit, err := item.Commit.Parent(i)
-			if err != nil {
-				return err
-			}
-			checkStack = append(checkStack, parentCommit.ID.String())
-		}
-	}
-	return nil
-}
-
 // getCommitIDsFromRepo get commit IDs from repo in between oldCommitID and newCommitID
 // isForcePush will be true if oldCommit isn't on the branch
 // Commit on baseBranch will skip
@@ -82,47 +30,33 @@ func getCommitIDsFromRepo(ctx context.Context, repo *repo_model.Repository, oldC
 		return nil, false, err
 	}
 
-	if err = oldCommit.LoadBranchName(); err != nil {
-		return nil, false, err
-	}
-
-	if len(oldCommit.Branch) == 0 {
-		commitIDs = make([]string, 2)
-		commitIDs[0] = oldCommitID
-		commitIDs[1] = newCommitID
-
-		return commitIDs, true, err
-	}
-
 	newCommit, err := gitRepo.GetCommit(newCommitID)
 	if err != nil {
 		return nil, false, err
 	}
 
-	commits, err := newCommit.CommitsBeforeUntil(oldCommitID)
+	isForcePush, err = newCommit.IsForcePush(oldCommitID)
 	if err != nil {
 		return nil, false, err
 	}
 
-	commitIDs = make([]string, 0, len(commits))
-	commitChecks := make(map[string]*commitBranchCheckItem)
+	if isForcePush {
+		commitIDs = make([]string, 2)
+		commitIDs[0] = oldCommitID
+		commitIDs[1] = newCommitID
 
-	for _, commit := range commits {
-		commitChecks[commit.ID.String()] = &commitBranchCheckItem{
-			Commit:  commit,
-			Checked: false,
-		}
+		return commitIDs, isForcePush, err
 	}
 
-	if err = commitBranchCheck(gitRepo, newCommit, oldCommitID, baseBranch, commitChecks); err != nil {
-		return
+	// Find commits between new and old commit exclusing base branch commits
+	commits, err := gitRepo.CommitsBetweenNotBase(newCommit, oldCommit, baseBranch)
+	if err != nil {
+		return nil, false, err
 	}
 
+	commitIDs = make([]string, 0, len(commits))
 	for i := len(commits) - 1; i >= 0; i-- {
-		commitID := commits[i].ID.String()
-		if item, ok := commitChecks[commitID]; ok && item.Checked {
-			commitIDs = append(commitIDs, commitID)
-		}
+		commitIDs = append(commitIDs, commits[i].ID.String())
 	}
 
 	return commitIDs, isForcePush, err
diff --git a/services/repository/push.go b/services/repository/push.go
index cdf030396..4b574e344 100644
--- a/services/repository/push.go
+++ b/services/repository/push.go
@@ -206,12 +206,12 @@ func pushUpdates(optsList []*repo_module.PushUpdateOptions) error {
 						return fmt.Errorf("newCommit.CommitsBeforeUntil: %w", err)
 					}
 
-					isForce, err := repo_module.IsForcePush(ctx, opts)
+					isForcePush, err := newCommit.IsForcePush(opts.OldCommitID)
 					if err != nil {
-						log.Error("isForcePush %s:%s failed: %v", repo.FullName(), branch, err)
+						log.Error("IsForcePush %s:%s failed: %v", repo.FullName(), branch, err)
 					}
 
-					if isForce {
+					if isForcePush {
 						log.Trace("Push %s is a force push", opts.NewCommitID)
 
 						cache.Remove(repo.GetCommitsCountCacheKey(opts.RefName(), true))