Improve context descendant sorting (#2579)

* Improve context descendant sorting

Topologically sort replies, then move self-replies to top of list

* Unify descendant sort passes

* Correct test package name

* Preallocate maps

1 files changed, 197 insertions, 0 deletions

diff --git a/internal/processing/status/get_test.go b/internal/processing/status/get_test.go
new file mode 100644
index 000000000..80482f1f2
--- /dev/null
+++ b/internal/processing/status/get_test.go
@@ -0,0 +1,197 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package status_test
+
+import (
+	"github.com/stretchr/testify/suite"
+	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+	"github.com/superseriousbusiness/gotosocial/internal/processing/status"
+	"testing"
+)
+
+type topoSortTestSuite struct {
+	suite.Suite
+}
+
+func statusIDs(apiStatuses []*apimodel.Status) []string {
+	ids := make([]string, 0, len(apiStatuses))
+	for _, apiStatus := range apiStatuses {
+		ids = append(ids, apiStatus.ID)
+	}
+	return ids
+}
+
+func (suite *topoSortTestSuite) TestBranched() {
+	// https://commons.wikimedia.org/wiki/File:Sorted_binary_tree_ALL_RGB.svg
+	f := &apimodel.Status{ID: "F"}
+	b := &apimodel.Status{ID: "B", InReplyToID: &f.ID}
+	a := &apimodel.Status{ID: "A", InReplyToID: &b.ID}
+	d := &apimodel.Status{ID: "D", InReplyToID: &b.ID}
+	c := &apimodel.Status{ID: "C", InReplyToID: &d.ID}
+	e := &apimodel.Status{ID: "E", InReplyToID: &d.ID}
+	g := &apimodel.Status{ID: "G", InReplyToID: &f.ID}
+	i := &apimodel.Status{ID: "I", InReplyToID: &g.ID}
+	h := &apimodel.Status{ID: "H", InReplyToID: &i.ID}
+
+	expected := statusIDs([]*apimodel.Status{f, b, a, d, c, e, g, i, h})
+	list := []*apimodel.Status{a, b, c, d, e, f, g, h, i}
+	status.TopoSort(list, "")
+	actual := statusIDs(list)
+
+	suite.Equal(expected, actual)
+}
+
+func (suite *topoSortTestSuite) TestBranchedWithSelfReplyChain() {
+	targetAccount := &apimodel.Account{ID: "1"}
+	otherAccount := &apimodel.Account{ID: "2"}
+
+	f := &apimodel.Status{
+		ID:      "F",
+		Account: targetAccount,
+	}
+	b := &apimodel.Status{
+		ID:                 "B",
+		Account:            targetAccount,
+		InReplyToID:        &f.ID,
+		InReplyToAccountID: &f.Account.ID,
+	}
+	a := &apimodel.Status{
+		ID:                 "A",
+		Account:            otherAccount,
+		InReplyToID:        &b.ID,
+		InReplyToAccountID: &b.Account.ID,
+	}
+	d := &apimodel.Status{
+		ID:                 "D",
+		Account:            targetAccount,
+		InReplyToID:        &b.ID,
+		InReplyToAccountID: &b.Account.ID,
+	}
+	c := &apimodel.Status{
+		ID:                 "C",
+		Account:            otherAccount,
+		InReplyToID:        &d.ID,
+		InReplyToAccountID: &d.Account.ID,
+	}
+	e := &apimodel.Status{
+		ID:                 "E",
+		Account:            targetAccount,
+		InReplyToID:        &d.ID,
+		InReplyToAccountID: &d.Account.ID,
+	}
+	g := &apimodel.Status{
+		ID:                 "G",
+		Account:            otherAccount,
+		InReplyToID:        &f.ID,
+		InReplyToAccountID: &f.Account.ID,
+	}
+	i := &apimodel.Status{
+		ID:                 "I",
+		Account:            targetAccount,
+		InReplyToID:        &g.ID,
+		InReplyToAccountID: &g.Account.ID,
+	}
+	h := &apimodel.Status{
+		ID:                 "H",
+		Account:            otherAccount,
+		InReplyToID:        &i.ID,
+		InReplyToAccountID: &i.Account.ID,
+	}
+
+	expected := statusIDs([]*apimodel.Status{f, b, d, e, c, a, g, i, h})
+	list := []*apimodel.Status{a, b, c, d, e, f, g, h, i}
+	status.TopoSort(list, targetAccount.ID)
+	actual := statusIDs(list)
+
+	suite.Equal(expected, actual)
+}
+
+func (suite *topoSortTestSuite) TestDisconnected() {
+	f := &apimodel.Status{ID: "F"}
+	b := &apimodel.Status{ID: "B", InReplyToID: &f.ID}
+	dID := "D"
+	e := &apimodel.Status{ID: "E", InReplyToID: &dID}
+
+	expected := statusIDs([]*apimodel.Status{e, f, b})
+	list := []*apimodel.Status{b, e, f}
+	status.TopoSort(list, "")
+	actual := statusIDs(list)
+
+	suite.Equal(expected, actual)
+}
+
+func (suite *topoSortTestSuite) TestTrivialCycle() {
+	xID := "X"
+	x := &apimodel.Status{ID: xID, InReplyToID: &xID}
+
+	expected := statusIDs([]*apimodel.Status{x})
+	list := []*apimodel.Status{x}
+	status.TopoSort(list, "")
+	actual := statusIDs(list)
+
+	suite.ElementsMatch(expected, actual)
+}
+
+func (suite *topoSortTestSuite) TestCycle() {
+	yID := "Y"
+	x := &apimodel.Status{ID: "X", InReplyToID: &yID}
+	y := &apimodel.Status{ID: yID, InReplyToID: &x.ID}
+
+	expected := statusIDs([]*apimodel.Status{x, y})
+	list := []*apimodel.Status{x, y}
+	status.TopoSort(list, "")
+	actual := statusIDs(list)
+
+	suite.ElementsMatch(expected, actual)
+}
+
+func (suite *topoSortTestSuite) TestMixedCycle() {
+	yID := "Y"
+	x := &apimodel.Status{ID: "X", InReplyToID: &yID}
+	y := &apimodel.Status{ID: yID, InReplyToID: &x.ID}
+	z := &apimodel.Status{ID: "Z"}
+
+	expected := statusIDs([]*apimodel.Status{x, y, z})
+	list := []*apimodel.Status{x, y, z}
+	status.TopoSort(list, "")
+	actual := statusIDs(list)
+
+	suite.ElementsMatch(expected, actual)
+}
+
+func (suite *topoSortTestSuite) TestEmpty() {
+	expected := statusIDs([]*apimodel.Status{})
+	list := []*apimodel.Status{}
+	status.TopoSort(list, "")
+	actual := statusIDs(list)
+
+	suite.Equal(expected, actual)
+}
+
+func (suite *topoSortTestSuite) TestNil() {
+	expected := statusIDs(nil)
+	var list []*apimodel.Status
+	status.TopoSort(list, "")
+	actual := statusIDs(list)
+
+	suite.Equal(expected, actual)
+}
+
+func TestTopoSortTestSuite(t *testing.T) {
+	suite.Run(t, &topoSortTestSuite{})
+}