From e641d0c5e9b4fcbbef5dbfeb30fd72ade3163ae9 Mon Sep 17 00:00:00 2001
From: Jason Bedard <jason+github@jbedard.ca>
Date: Thu, 3 Aug 2017 01:04:37 -0700
Subject: [PATCH] perf($rootScope): allow $watchCollection use of expression
 input watching

By adding a $$pure flag to the $watchCollectionInterceptor to shallow
watch all inputs regardless of type when watching an object/array
literal.
---
 src/ng/parse.js     | 9 +++++++--
 src/ng/rootScope.js | 6 +++++-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/ng/parse.js b/src/ng/parse.js
index f173eed527d8..9f8621440cf3 100644
--- a/src/ng/parse.js
+++ b/src/ng/parse.js
@@ -1944,6 +1944,7 @@ function $ParseProvider() {
         return second(first(value));
       }
       chainedInterceptor.$stateful = first.$stateful || second.$stateful;
+      chainedInterceptor.$$pure = first.$$pure && second.$$pure;
 
       return chainedInterceptor;
     }
@@ -1979,14 +1980,18 @@ function $ParseProvider() {
       // If the expression itself has no inputs then use the full expression as an input.
       if (!interceptorFn.$stateful) {
         useInputs = !parsedExpression.inputs;
-        fn.inputs = (parsedExpression.inputs ? parsedExpression.inputs : [parsedExpression]).map(function(e) {
+        fn.inputs = parsedExpression.inputs ? parsedExpression.inputs : [parsedExpression];
+
+        if (!interceptorFn.$$pure) {
+          fn.inputs = fn.inputs.map(function(e) {
               // Remove the isPure flag of inputs when it is not absolute because they are now wrapped in a
-              // potentially non-pure interceptor function.
+              // non-pure interceptor function.
               if (e.isPure === PURITY_RELATIVE) {
                 return function depurifier(s) { return e(s); };
               }
               return e;
             });
+        }
       }
 
       return addWatchDelegate(fn);
diff --git a/src/ng/rootScope.js b/src/ng/rootScope.js
index bb7f83b42462..5bb68c732846 100644
--- a/src/ng/rootScope.js
+++ b/src/ng/rootScope.js
@@ -581,7 +581,11 @@ function $RootScopeProvider() {
        *    de-registration function is executed, the internal watch operation is terminated.
        */
       $watchCollection: function(obj, listener) {
-        $watchCollectionInterceptor.$stateful = true;
+        // Mark the interceptor as
+        // ... $$pure when literal since the instance will change when any input changes
+        $watchCollectionInterceptor.$$pure = $parse(obj).literal;
+        // ... $stateful when non-literal since we must read the state of the collection
+        $watchCollectionInterceptor.$stateful = !$watchCollectionInterceptor.$$pure;
 
         var self = this;
         // the current value, updated on each dirty-check run