wip: check duplicate keys

packages/runtime-vapor/__tests__/for.spec.ts

@@ -1287,7 +1287,22 @@ describe('createFor', () => {
       expect(updatedChild).toBe(firstChild)
     })
 
-    test.todo('should warn with duplicate keys', async () => {})
+    test('should warn with duplicate keys', async () => {
+      const arr = ref<number[]>([1, 2, 3])
+      const { host, html } = render(arr)
+      expect(host.children.length).toBe(3)
+      expect(html()).toBe(
+        `<span>1</span><span>2</span><span>3</span><!--for-->`,
+      )
+
+      arr.value = [1, 2, 2]
+      await nextTick()
+      expect(host.children.length).toBe(3)
+      expect(html()).toBe(
+        `<span>1</span><span>2</span><span>2</span><!--for-->`,
+      )
+      expect(`Duplicate keys`).toHaveBeenWarned()
+    })
   })
 
   describe.todo('renderer: unkeyed children', () => {})

packages/runtime-vapor/src/apiCreateFor.ts

@@ -150,6 +150,24 @@ export const createFor = (
           unmount(oldBlocks[i])
         }
       } else {
+        if (__DEV__) {
+          const keyToIndexMap: Map<any, number> = new Map()
+          for (let i = 0; i < newLength; i++) {
+            const item = getItem(source, i)
+            const key = getKey(...item)
+            if (key != null) {
+              if (keyToIndexMap.has(key)) {
+                warn(
+                  `Duplicate keys found during update:`,
+                  JSON.stringify(key),
+                  `Make sure keys are unique.`,
+                )
+              }
+              keyToIndexMap.set(key, i)
+            }
+          }
+        }
+
         const sharedBlockCount = Math.min(oldLength, newLength)
         const previousKeyIndexPairs: [any, number][] = new Array(oldLength)
         const queuedBlocks: [