perf($compile): only re-$interpolate attribute values at link time if changed since compile

Author: jbedard

benchmarks/largetable-bp/main.html

@@ -14,6 +14,7 @@
       <div>ngBind: <input type="radio" ng-model="benchmarkType" value="ngBind"></div>
       <div>ngBindOnce: <input type="radio" ng-model="benchmarkType" value="ngBindOnce"></div>
       <div>interpolation: <input type="radio" ng-model="benchmarkType" value="interpolation"></div>
+      <div>attribute interpolation: <input type="radio" ng-model="benchmarkType" value="interpolationAttr"></div>
       <div>ngBind + fnInvocation: <input type="radio" ng-model="benchmarkType" value="ngBindFn"></div>
       <div>interpolation + fnInvocation: <input type="radio" ng-model="benchmarkType" value="interpolationFn"></div>
       <div>ngBind + filter: <input type="radio" ng-model="benchmarkType" value="ngBindFilter"></div>
@@ -46,6 +47,12 @@ <h2>baseline interpolation</h2>
             <span ng-repeat="column in row">{{column.i}}:{{column.j}}|</span>
           </div>
         </div>
+        <div ng-switch-when="interpolationAttr">
+          <h2>attribute interpolation</h2>
+          <div ng-repeat="row in data">
+            <span ng-repeat="column in row" i="{{column.i}}" j="{{column.j}}">i,j attrs</span>
+          </div>
+        </div>
         <div ng-switch-when="ngBindFn">
           <h2>bindings with functions</h2>
           <div ng-repeat="row in data">

src/ng/compile.js

@@ -2335,7 +2335,10 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
 
 
     function addAttrInterpolateDirective(node, directives, value, name, allOrNothing) {
-      var interpolateFn = $interpolate(value, true);
+      var trustedContext = getTrustedContext(node, name);
+      allOrNothing = ALL_OR_NOTHING_ATTRS[name] || allOrNothing;
+
+      var interpolateFn = $interpolate(value, true, trustedContext, allOrNothing);
 
       // no interpolation found -> ignore
       if (!interpolateFn) return;
@@ -2360,16 +2363,16 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
                           "ng- versions (such as ng-click instead of onclick) instead.");
                 }
 
-                // If the attribute was removed, then we are done
-                if (!attr[name]) {
-                  return;
+                // If the attribute has changed since last $interpolate()ed
+                var newValue = attr[name];
+                if (newValue !== value) {
+                  // we need to interpolate again since the attribute value has been updated
+                  // (e.g. by another directive's compile function)
+                  // ensure unset/empty values make interpolateFn falsy
+                  interpolateFn = newValue && $interpolate(newValue, true, trustedContext, allOrNothing);
+                  value = newValue;
                 }
 
-                // we need to interpolate again, in case the attribute value has been updated
-                // (e.g. by another directive's compile function)
-                interpolateFn = $interpolate(attr[name], true, getTrustedContext(node, name),
-                    ALL_OR_NOTHING_ATTRS[name] || allOrNothing);
-
                 // if attribute was updated so that there is no interpolation going on we don't want to
                 // register any observers
                 if (!interpolateFn) return;