#306

frontend/src/pages/materials/MaterialListPage.tsx

@@ -106,7 +106,7 @@ const clearedTagSelectionPath = (
     const qs = new URLSearchParams (locationSearch)
     qs.delete ('tag_id')
     qs.delete ('include_descendants')
-    qs.set ('group_by', 'none')
+    qs.delete ('group_by')
     qs.delete ('page')
     qs.set ('material_filter', materialFilter)
     return `/materials?${ qs.toString () }`
@@ -471,6 +471,18 @@ const MaterialListPage: FC = () => {
 		  タグ選択を解除
 		</PrefetchLink>
 	      </div>)}
+	  {(tagId != null && tagScope == null) && (
+	      <div className="flex flex-wrap items-center gap-3 rounded-lg border
+			      border-amber-200 bg-amber-50 px-4 py-3 text-sm text-amber-900
+			      dark:border-amber-800 dark:bg-amber-950 dark:text-amber-100">
+		<span>選択中タグが見つかりません．</span>
+		<PrefetchLink
+		    to={clearedTagSelectionPath (location.search, materialFilter)}
+		    className="font-medium underline underline-offset-2
+			       text-amber-800 dark:text-amber-200">
+		  タグ選択を解除
+		</PrefetchLink>
+	      </div>)}
 
 	  {tagState === 'untagged' && (
 	      <PrefetchLink