fix: pick up prototype-inherited properties in toMatchObject diff (fix #6939)

packages/expect/src/jest-utils.ts

@@ -783,27 +783,33 @@ export function getObjectSubset(
             })
           }
 
-          for (const key of getObjectKeys(object)) {
-            if (hasPropertyInObject(subset, key)) {
+          // Iterate subset's keys (not object's own enumerable keys) so that
+          // inherited/accessor properties -- e.g. DOM element properties
+          // like `tagName`, which live on the prototype chain -- are still
+          // picked up via the `in` operator. See #6939.
+          for (const key of getObjectKeys(subset)) {
+            if (key in object) {
               trimmed[key] = seenReferences.has(object[key])
                 ? seenReferences.get(object[key])
                 : getObjectSubsetWithContext(seenReferences)(
                     object[key],
                     subset[key],
                   )
             }
-            else {
-              if (!seenReferences.has(object[key])) {
-                stripped += 1
-                if (isObject(object[key])) {
-                  stripped += getObjectKeys(object[key]).length
-                }
-
-                getObjectSubsetWithContext(seenReferences)(
-                  object[key],
-                  subset[key],
-                )
+          }
+
+          // Preserve "N properties omitted from actual" messaging by still
+          // counting object's own extra keys not present in subset.
+          for (const key of getObjectKeys(object)) {
+            if (!hasPropertyInObject(subset, key) && !seenReferences.has(object[key])) {
+              stripped += 1
+              if (isObject(object[key])) {
+                stripped += getObjectKeys(object[key]).length
               }
+              getObjectSubsetWithContext(seenReferences)(
+                object[key],
+                subset[key],
+              )
             }
           }
 

test/unit/test/jest-expect.test.ts

@@ -1747,6 +1747,37 @@ it('toMatchObject error diff', () => {
       }",
     ]
   `)
+  // https://github.com/vitest-dev/vitest/issues/6939
+  // properties inherited via the prototype chain (e.g. DOM elements) should
+  // still be picked up when building the toMatchObject diff, instead of
+  // falling back to showing the raw object.
+  {
+    const proto = {
+      get tagName() {
+        return 'DIV'
+      },
+    }
+    const domLike = Object.create(proto)
+    domLike.id = 'root'
+
+    expect(domLike).toMatchObject({ tagName: 'DIV', id: 'root' })
+
+    expect(getError(() =>
+      expect(domLike).toMatchObject({ tagName: 'SPAN', id: 'root' }),
+    )).toMatchInlineSnapshot(`
+      [
+        "expected { id: 'root' } to match object { tagName: 'SPAN', id: 'root' }",
+        "- Expected
+      + Received
+
+        {
+          "id": "root",
+      -   "tagName": "SPAN",
+      +   "tagName": "DIV",
+        }",
+      ]
+    `)
+  }
 })
 
 it('toHaveProperty error diff', () => {