fix: props merge order. #967 (#968)

Author: theKashey

Diff for: src/reconciler/hotReplacementRender.js

@@ -261,18 +261,20 @@ const hotReplacementRender = (instance, stack) => {
     const next = instance => {
       // copy over props as long new component may be hidden inside them
       // child does not have all props, as long some of them can be calculated on componentMount.
+      const realProps = instance.props
       const nextProps = {
-        ...instance.props,
+        ...realProps,
         ...(child.nextProps || {}),
         ...(child.props || {}),
       }
 
       if (isReactClass(instance) && instance.componentWillUpdate) {
         // Force-refresh component (bypass redux renderedComponent)
-        instance.componentWillUpdate(nextProps, instance.state)
+        instance.componentWillUpdate({ ...realProps }, instance.state)
       }
       instance.props = nextProps
       hotReplacementRender(instance, stackChild)
+      instance.props = realProps
     }
 
     // text node

Diff for: test/reconciler.test.js

@@ -128,7 +128,7 @@ describe('reconciler', () => {
 
       // what props should be used? Look like the new ones
       expect(second.willUpdate.mock.calls[0]).toEqual([
-        { children: '42', newProp: true, keyId: '2' },
+        { children: '42', keyId: '1' },
         null,
         { children: '42', keyId: '1' },
         null,
@@ -137,7 +137,7 @@ describe('reconciler', () => {
       expect(second.willUpdate.mock.calls[1]).toEqual([
         { children: '42', newProp: true, keyId: '2' },
         null,
-        expect.any(Object), // Flake in React 15. Should be { children: '42', keyId: "1" },
+        { children: '42', keyId: '1' },
         null,
       ])