Only check equality on final props if custom mergeProps is supplied

Author: tgriesser

src/components/connect.js

@@ -39,11 +39,22 @@ export default function connect(mapStateToProps, mapDispatchToProps, mergeProps,
     mapDispatchToProps || defaultMapDispatchToProps
 
   const finalMergeProps = mergeProps || defaultMergeProps
+  const checkMergedEquals = finalMergeProps !== defaultMergeProps
   const { pure = true, withRef = false } = options
 
   // Helps track hot reloading.
   const version = nextVersion++
 
+  function computeMergedProps(stateProps, dispatchProps, parentProps) {
+    const mergedProps = finalMergeProps(stateProps, dispatchProps, parentProps)
+    invariant(
+      isPlainObject(mergedProps),
+      '`mergeProps` must return an object. Instead received %s.',
+      mergedProps
+    )
+    return mergedProps
+  }
+
   return function wrapWithConnect(WrappedComponent) {
     class Connect extends Component {
       shouldComponentUpdate() {
@@ -106,16 +117,6 @@ export default function connect(mapStateToProps, mapDispatchToProps, mergeProps,
         return isFactory ? this.computeDispatchProps(store, props) : checkStateShape(mappedDispatch, true)
       }
 
-      computeMergedProps(stateProps, dispatchProps, parentProps) {
-        const mergedProps = finalMergeProps(stateProps, dispatchProps, parentProps)
-        invariant(
-          isPlainObject(mergedProps),
-          '`mergeProps` must return an object. Instead received %s.',
-          mergedProps
-        )
-        return mergedProps
-      }
-
       updateStatePropsIfNeeded() {
         const nextStateProps = this.computeStateProps(this.store, this.props)
         if (this.stateProps && shallowEqual(nextStateProps, this.stateProps)) {
@@ -137,8 +138,8 @@ export default function connect(mapStateToProps, mapDispatchToProps, mergeProps,
       }
 
       updateMergedPropsIfNeeded() {
-        const nextMergedProps = this.computeMergedProps(this.stateProps, this.dispatchProps, this.props)
-        if (this.mergedProps && shallowEqual(nextMergedProps, this.mergedProps)) {
+        const nextMergedProps = computeMergedProps(this.stateProps, this.dispatchProps, this.props)
+        if (this.mergedProps && checkMergedEquals && shallowEqual(nextMergedProps, this.mergedProps)) {
           return false
         }