Display conflict-free merge messages for pull requests (#15773)

Repositories using external issue tracker tend to use numeric issues in
commits. To prevent conflicts during issue reference parsing or inside
commit hooks, this change respects these configuration and uses the !
character to refer to pull requests in merge commit messages.

For repositories using squash merges, this was already handled.

Signed-off-by: JustusBunsi <61625851+justusbunsi@users.noreply.github.com>
Co-authored-by: zeripath <art27@cantab.net>

2 files changed, 44 insertions, 2 deletions

diff --git a/models/pull.go b/models/pull.go
index 133f196aae..a1fd7c3e41 100644
--- a/models/pull.go
+++ b/models/pull.go
@@ -212,12 +212,21 @@ func (pr *PullRequest) GetDefaultMergeMessage() string {
 		log.Error("Cannot load issue %d for PR id %d: Error: %v", pr.IssueID, pr.ID, err)
 		return ""
 	}
+	if err := pr.LoadBaseRepo(); err != nil {
+		log.Error("LoadBaseRepo: %v", err)
+		return ""
+	}
+
+	issueReference := "#"
+	if pr.BaseRepo.UnitEnabled(UnitTypeExternalTracker) {
+		issueReference = "!"
+	}
 
 	if pr.BaseRepoID == pr.HeadRepoID {
-		return fmt.Sprintf("Merge pull request '%s' (#%d) from %s into %s", pr.Issue.Title, pr.Issue.Index, pr.HeadBranch, pr.BaseBranch)
+		return fmt.Sprintf("Merge pull request '%s' (%s%d) from %s into %s", pr.Issue.Title, issueReference, pr.Issue.Index, pr.HeadBranch, pr.BaseBranch)
 	}
 
-	return fmt.Sprintf("Merge pull request '%s' (#%d) from %s:%s into %s", pr.Issue.Title, pr.Issue.Index, pr.HeadRepo.FullName(), pr.HeadBranch, pr.BaseBranch)
+	return fmt.Sprintf("Merge pull request '%s' (%s%d) from %s:%s into %s", pr.Issue.Title, issueReference, pr.Issue.Index, pr.HeadRepo.FullName(), pr.HeadBranch, pr.BaseBranch)
 }
 
 // ReviewCount represents a count of Reviews
diff --git a/models/pull_test.go b/models/pull_test.go
index 3cc6abfec7..5eaeb60e67 100644
--- a/models/pull_test.go
+++ b/models/pull_test.go
@@ -234,3 +234,36 @@ func TestPullRequest_GetWorkInProgressPrefixWorkInProgress(t *testing.T) {
 	pr.Issue.Title = "[wip] " + original
 	assert.Equal(t, "[wip]", pr.GetWorkInProgressPrefix())
 }
+
+func TestPullRequest_GetDefaultMergeMessage_InternalTracker(t *testing.T) {
+	assert.NoError(t, PrepareTestDatabase())
+	pr := AssertExistsAndLoadBean(t, &PullRequest{ID: 2}).(*PullRequest)
+
+	assert.Equal(t, "Merge pull request 'issue3' (#3) from branch2 into master", pr.GetDefaultMergeMessage())
+
+	pr.BaseRepoID = 1
+	pr.HeadRepoID = 2
+	assert.Equal(t, "Merge pull request 'issue3' (#3) from user2/repo1:branch2 into master", pr.GetDefaultMergeMessage())
+}
+
+func TestPullRequest_GetDefaultMergeMessage_ExternalTracker(t *testing.T) {
+	assert.NoError(t, PrepareTestDatabase())
+
+	externalTracker := RepoUnit{
+		Type: UnitTypeExternalTracker,
+		Config: &ExternalTrackerConfig{
+			ExternalTrackerFormat: "https://someurl.com/{user}/{repo}/{issue}",
+		},
+	}
+	baseRepo := &Repository{Name: "testRepo", ID: 1}
+	baseRepo.Owner = &User{Name: "testOwner"}
+	baseRepo.Units = []*RepoUnit{&externalTracker}
+
+	pr := AssertExistsAndLoadBean(t, &PullRequest{ID: 2, BaseRepo: baseRepo}).(*PullRequest)
+
+	assert.Equal(t, "Merge pull request 'issue3' (!3) from branch2 into master", pr.GetDefaultMergeMessage())
+
+	pr.BaseRepoID = 1
+	pr.HeadRepoID = 2
+	assert.Equal(t, "Merge pull request 'issue3' (!3) from user2/repo1:branch2 into master", pr.GetDefaultMergeMessage())
+}