From 142340e0ff035c01c66143c44b457928ba153195 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jean-Philippe=20Qu=C3=A9m=C3=A9ner?=
 <JohnnyQQQQ@users.noreply.github.com>
Date: Mon, 10 Nov 2025 20:37:02 +0100
Subject: [PATCH] refactor(folders): use set to detect circular references
 (#113665)

---
 .../folder/folderimpl/unifiedstore.go         |   9 +-
 .../folder/folderimpl/unifiedstore_test.go    | 135 ++++++++++++++++++
 2 files changed, 139 insertions(+), 5 deletions(-)

diff --git a/pkg/services/folder/folderimpl/unifiedstore.go b/pkg/services/folder/folderimpl/unifiedstore.go
index 8c30024eefb..4c76b219873 100644
--- a/pkg/services/folder/folderimpl/unifiedstore.go
+++ b/pkg/services/folder/folderimpl/unifiedstore.go
@@ -568,14 +568,13 @@ func buildFolderFullPaths(f *folder.Folder, relations map[string]string, folderM
 	titles = append(titles, f.Title)
 	uids = append(uids, f.UID)
 
-	i := 0
+	seen := make(map[string]bool)
 	currentUID := f.UID
 	for currentUID != "" {
-		// This is just a circuit breaker to prevent infinite loops. We should never reach this limit.
-		if i > 1000 {
-			return fmt.Errorf("folder depth exceeds the maximum allowed depth, You might have a circular reference")
+		if seen[currentUID] {
+			return folder.ErrCircularReference.Errorf("circular reference detected for folder %s", currentUID)
 		}
-		i++
+		seen[currentUID] = true
 		parentUID, exists := relations[currentUID]
 		if !exists {
 			break
diff --git a/pkg/services/folder/folderimpl/unifiedstore_test.go b/pkg/services/folder/folderimpl/unifiedstore_test.go
index 5ffc1d12947..b31db85227e 100644
--- a/pkg/services/folder/folderimpl/unifiedstore_test.go
+++ b/pkg/services/folder/folderimpl/unifiedstore_test.go
@@ -891,6 +891,141 @@ func TestBuildFolderFullPaths(t *testing.T) {
 	}
 }
 
+func TestBuildFolderFullPaths_CircularReference(t *testing.T) {
+	type args struct {
+		f         *folder.Folder
+		relations map[string]string
+		folderMap map[string]*folder.Folder
+	}
+	tests := []struct {
+		name        string
+		args        args
+		expectedErr string
+	}{
+		{
+			name: "should detect direct circular reference (A -> B -> A)",
+			args: args{
+				f: &folder.Folder{
+					Title:     "FolderA",
+					UID:       "folder-a",
+					ParentUID: "folder-b",
+				},
+				relations: map[string]string{
+					"folder-a": "folder-b",
+					"folder-b": "folder-a", // circular: B points back to A
+				},
+				folderMap: map[string]*folder.Folder{
+					"folder-a": {
+						Title:     "FolderA",
+						UID:       "folder-a",
+						ParentUID: "folder-b",
+					},
+					"folder-b": {
+						Title:     "FolderB",
+						UID:       "folder-b",
+						ParentUID: "folder-a",
+					},
+				},
+			},
+			expectedErr: "circular reference detected",
+		},
+		{
+			name: "should detect self-reference (A -> A)",
+			args: args{
+				f: &folder.Folder{
+					Title:     "FolderA",
+					UID:       "folder-a",
+					ParentUID: "folder-a", // points to itself
+				},
+				relations: map[string]string{
+					"folder-a": "folder-a",
+				},
+				folderMap: map[string]*folder.Folder{
+					"folder-a": {
+						Title:     "FolderA",
+						UID:       "folder-a",
+						ParentUID: "folder-a",
+					},
+				},
+			},
+			expectedErr: "circular reference detected",
+		},
+		{
+			name: "should detect longer circular reference (A -> B -> C -> A)",
+			args: args{
+				f: &folder.Folder{
+					Title:     "FolderA",
+					UID:       "folder-a",
+					ParentUID: "folder-b",
+				},
+				relations: map[string]string{
+					"folder-a": "folder-b",
+					"folder-b": "folder-c",
+					"folder-c": "folder-a", // circular: C points back to A
+				},
+				folderMap: map[string]*folder.Folder{
+					"folder-a": {
+						Title:     "FolderA",
+						UID:       "folder-a",
+						ParentUID: "folder-b",
+					},
+					"folder-b": {
+						Title:     "FolderB",
+						UID:       "folder-b",
+						ParentUID: "folder-c",
+					},
+					"folder-c": {
+						Title:     "FolderC",
+						UID:       "folder-c",
+						ParentUID: "folder-a",
+					},
+				},
+			},
+			expectedErr: "circular reference detected",
+		},
+		{
+			name: "should detect circular reference starting from middle (B in A -> B -> C -> A)",
+			args: args{
+				f: &folder.Folder{
+					Title:     "FolderB",
+					UID:       "folder-b",
+					ParentUID: "folder-c",
+				},
+				relations: map[string]string{
+					"folder-a": "folder-b",
+					"folder-b": "folder-c",
+					"folder-c": "folder-a",
+				},
+				folderMap: map[string]*folder.Folder{
+					"folder-a": {
+						Title:     "FolderA",
+						UID:       "folder-a",
+						ParentUID: "folder-b",
+					},
+					"folder-b": {
+						Title:     "FolderB",
+						UID:       "folder-b",
+						ParentUID: "folder-c",
+					},
+					"folder-c": {
+						Title:     "FolderC",
+						UID:       "folder-c",
+						ParentUID: "folder-a",
+					},
+				},
+			},
+			expectedErr: "circular reference detected",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := buildFolderFullPaths(tt.args.f, tt.args.relations, tt.args.folderMap)
+			require.Error(t, err)
+			require.Contains(t, err.Error(), tt.expectedErr)
+		})
+	}
+}
+
 func TestList(t *testing.T) {
 	type args struct {
 		ctx   context.Context