feat(compiler): Pre-compile Scope.watch ASTs for attribute mustaches

For dart-archive#1086

Author: jbdeboer

lib/core_dom/element_binder.dart

@@ -254,10 +254,8 @@ class ElementBinder {
       if (nodesAttrsDirectives.isEmpty) {
         nodeModule.bind(AttrMustache, toFactory: (Injector injector) {
           var scope = injector.getByKey(_SCOPE_KEY);
-          var interpolate = injector.getByKey(_INTERPOLATE_KEY);
           for (var ref in nodesAttrsDirectives) {
-            new AttrMustache(nodeAttrs, ref.value, interpolate, scope,
-                injector.getByKey(_FORMATTER_MAP_KEY));
+            new AttrMustache(nodeAttrs, ref.value, ref.valueAST, scope);
           }
         });
       }

lib/core_dom/mustache.dart

@@ -26,21 +26,16 @@ class AttrMustache {
 
   // This Directive is special and does not go through injection.
   AttrMustache(this._attrs,
-                          String template,
-                          Interpolate interpolate,
-                          Scope scope,
-                          FormatterMap formatters) {
-    var eqPos = template.indexOf('=');
-    _attrName = template.substring(0, eqPos);
-    String expression = interpolate(template.substring(eqPos + 1));
-
-    _updateMarkup('', template);
+                          String this._attrName,
+                          AST valueAST,
+                          Scope scope) {
+    _updateMarkup('', 'INITIAL-VALUE');
 
     _attrs.listenObserverChanges(_attrName, (hasObservers) {
     if (_hasObservers != hasObservers) {
       _hasObservers = hasObservers;
       if (_watch != null) _watch.remove();
-        _watch = scope.watch(expression, _updateMarkup, formatters: formatters,
+        _watch = scope.watchAST(valueAST, _updateMarkup,
             canChangeModel: _hasObservers);
       }
     });

lib/core_dom/selector.dart

@@ -98,8 +98,12 @@ class DirectiveSelector {
           // we need to pass the name to the directive by prefixing it to
           // the value. Yes it is a bit of a hack.
           _directives[selectorRegExp.annotation].forEach((type) {
+            // Pre-compute the AST to watch this value.
+            String expression = _interpolate(value);
+            AST valueAST = _astParser(expression, formatters: _formatters);
+
             builder.addDirective(new DirectiveRef(
-                node, type, selectorRegExp.annotation, new Key(type), '$attrName=$value'));
+                node, type, selectorRegExp.annotation, new Key(type), attrName, valueAST));
           });
         }
       }

test/core_dom/selector_spec.dart

@@ -123,7 +123,9 @@ main() {
       it('should match attributes', () {
         expect(selector(element = e('<div attr="before-xyz-after"></div>')),
         toEqualsDirectiveInfos([
-            { "selector": '[*=/xyz/]', "value": 'attr=before-xyz-after',
+            { "selector": '[*=/xyz/]',
+                "value": 'attr',
+                "ast": '"before-xyz-after"',
                 "element": element, "name": 'attr'}
         ]));
       });