Add an exception to the insignificant-slice rule when the only usag…

…e site is the App layer

.changeset/ten-weeks-drive.md

@@ -0,0 +1,5 @@
+---
+'@feature-sliced/steiger-plugin': patch
+---
+
+Add an exception to the `insignificant-slice` rule when the only usage site is the App layer

packages/steiger-plugin-fsd/src/insignificant-slice/index.spec.ts

@@ -33,6 +33,9 @@ vi.mock('node:fs', async (importOriginal) => {
       '/features/comments/ui/CommentCard.tsx': '',
       '/features/comments/index.ts': '',
 
+      '/widgets/sidebar/ui/Sidebar.tsx': '',
+      '/widgets/sidebar/index.ts': '',
+
       '/pages/editor/ui/EditorPage.tsx':
         'import { Button } from "@/shared/ui"; import { Editor } from "./Editor"; import { CommentCard } from "@/features/comments"; import { UserAvatar } from "@/entities/user"',
       '/pages/editor/ui/Editor.tsx':
@@ -43,6 +46,8 @@ vi.mock('node:fs', async (importOriginal) => {
       '/pages/settings/index.ts': '',
       '/pages/home/index.ts': '',
       '/pages/category/index.ts': '',
+
+      '/app/layouts/BaseLayout.tsx': 'import { Sidebar } from "@/widgets/sidebar"',
     },
     originalFs,
   )
@@ -95,6 +100,21 @@ it('reports no errors on a project with no insignificant slices', async () => {
   expect((await insignificantSlice.check(root)).diagnostics).toEqual([])
 })
 
+it('reports no errors when the only usage of a slice is on the App layer', async () => {
+  const root = parseIntoFsdRoot(`
+    📂 widgets
+      📂 sidebar
+        📂 ui
+          📄 Sidebar.tsx
+        📄 index.ts
+    📂 app
+      📂 layouts
+        📄 BaseLayout.tsx
+  `)
+
+  expect((await insignificantSlice.check(root)).diagnostics).toEqual([])
+})
+
 it('reports errors on a project with insignificant slices', async () => {
   const root = parseIntoFsdRoot(`
     📂 shared

packages/steiger-plugin-fsd/src/insignificant-slice/index.ts

@@ -27,10 +27,12 @@ const insignificantSlice = {
       if (targetLocationKeys.size === 1) {
         const referenceLocationKey = [...targetLocationKeys][0]
         if (unslicedLayers.includes(referenceLocationKey)) {
-          diagnostics.push({
-            message: `This slice has only one reference on layer "${referenceLocationKey}". Consider moving this code to "${referenceLocationKey}".`,
-            location: { path: join(root.path, sourceLocationKey) },
-          })
+          if (referenceLocationKey !== 'app') {
+            diagnostics.push({
+              message: `This slice has only one reference on layer "${referenceLocationKey}". Consider moving this code to "${referenceLocationKey}".`,
+              location: { path: join(root.path, sourceLocationKey) },
+            })
+          }
         } else {
           diagnostics.push({
             message: `This slice has only one reference in slice "${referenceLocationKey}". Consider merging them.`,