2 files changed, 61 insertions, 7 deletions
diff --git a/internal/processing/status/create.go b/internal/processing/status/create.go
index b450e4bdd..737755852 100644
--- a/internal/processing/status/create.go
+++ b/internal/processing/status/create.go
@@ -190,18 +190,28 @@ func (p *Processor) processReplyToID(ctx context.Context, form *apimodel.Advance
 }
 
 func (p *Processor) processThreadID(ctx context.Context, status *gtsmodel.Status) gtserror.WithCode {
-	// Status takes the thread ID
-	// of whatever it replies to.
-	if status.InReplyTo != nil {
+	// Status takes the thread ID of
+	// whatever it replies to, if set.
+	//
+	// Might not be set if status is local
+	// and replies to a remote status that
+	// doesn't have a thread ID yet.
+	//
+	// If so, we can just thread from this
+	// status onwards instead, since this
+	// is where the relevant part of the
+	// thread starts, from the perspective
+	// of our instance at least.
+	if status.InReplyTo != nil &&
+		status.InReplyTo.ThreadID != "" {
+		// Just inherit threadID from parent.
 		status.ThreadID = status.InReplyTo.ThreadID
 		return nil
 	}
 
-	// Status doesn't reply to anything,
-	// so it's a new local top-level status
-	// and therefore needs a thread ID.
+	// Mark new thread (or threaded
+	// subsection) starting from here.
 	threadID := id.NewULID()
-
 	if err := p.state.DB.PutThread(
 		ctx,
 		&gtsmodel.Thread{
diff --git a/internal/processing/status/create_test.go b/internal/processing/status/create_test.go
index 8d4267585..e32d8bc52 100644
--- a/internal/processing/status/create_test.go
+++ b/internal/processing/status/create_test.go
@@ -242,6 +242,50 @@ func (suite *StatusCreateTestSuite) TestProcessLanguageWithScriptPart() {
 	suite.Equal("zh-Hans", *apiStatus.Language)
 }
 
+func (suite *StatusCreateTestSuite) TestProcessReplyToUnthreadedRemoteStatus() {
+	ctx := context.Background()
+
+	creatingAccount := suite.testAccounts["local_account_1"]
+	creatingApplication := suite.testApplications["application_1"]
+	inReplyTo := suite.testStatuses["remote_account_1_status_1"]
+
+	// Reply to a remote status that
+	// doesn't have a threadID set on it.
+	statusCreateForm := &apimodel.AdvancedStatusCreateForm{
+		StatusCreateRequest: apimodel.StatusCreateRequest{
+			Status:      "boobies",
+			MediaIDs:    []string{},
+			Poll:        nil,
+			InReplyToID: inReplyTo.ID,
+			Sensitive:   false,
+			SpoilerText: "this is a reply",
+			Visibility:  apimodel.VisibilityPublic,
+			ScheduledAt: "",
+			Language:    "en",
+			ContentType: apimodel.StatusContentTypePlain,
+		},
+		AdvancedVisibilityFlagsForm: apimodel.AdvancedVisibilityFlagsForm{
+			Federated: nil,
+			Boostable: nil,
+			Replyable: nil,
+			Likeable:  nil,
+		},
+	}
+
+	apiStatus, err := suite.status.Create(ctx, creatingAccount, creatingApplication, statusCreateForm)
+	suite.NoError(err)
+	suite.NotNil(apiStatus)
+
+	// ThreadID should be set on the status,
+	// even though the replied-to status does
+	// not have a threadID.
+	dbStatus, dbErr := suite.state.DB.GetStatusByID(ctx, apiStatus.ID)
+	if dbErr != nil {
+		suite.FailNow(err.Error())
+	}
+	suite.NotEmpty(dbStatus.ThreadID)
+}
+
 func TestStatusCreateTestSuite(t *testing.T) {
 	suite.Run(t, new(StatusCreateTestSuite))
 }