feat($compile): simplify isolate scope bindings

Changed the isolate scope binding options to:
  - @attr - attribute binding (including interpolation)
  - =model - by-directional model binding
  - &expr - expression execution binding

This change simplifies the terminology as well as
number of choices available to the developer. It
also supports local name aliasing from the parent.

BREAKING CHANGE: isolate scope bindings definition has changed and
the inject option for the directive controller injection was removed.

To migrate the code follow the example below:

Before:

scope: {
  myAttr: 'attribute',
  myBind: 'bind',
  myExpression: 'expression',
  myEval: 'evaluate',
  myAccessor: 'accessor'
}

After:

scope: {
  myAttr: '@',
  myBind: '@',
  myExpression: '&',
  // myEval - usually not useful, but in cases where the expression is assignable, you can use '='
  myAccessor: '=' // in directive's template change myAccessor() to myAccessor
}

The removed `inject` wasn't generaly useful for directives so there should be no code using it.

2 files changed, 80 insertions, 62 deletions

diff --git a/src/ng/compile.js b/src/ng/compile.js
index ee120263..e1aba35b 100644
--- a/src/ng/compile.js
+++ b/src/ng/compile.js
@@ -18,6 +18,9 @@
  */
 
 
+var NON_ASSIGNABLE_MODEL_EXPRESSION = 'Non-assignable model expression: ';
+
+
 /**
  * @ngdoc function
  * @name angular.module.ng.$compile
@@ -225,47 +228,6 @@ function $CompileProvider($provide) {
     function($injector,   $interpolate,   $exceptionHandler,   $http,   $templateCache,   $parse,
              $controller,   $rootScope) {
 
-    var LOCAL_MODE = {
-      attribute: function(localName, mode, parentScope, scope, attr) {
-        scope[localName] = attr[localName];
-      },
-
-      evaluate: function(localName, mode, parentScope, scope, attr) {
-        scope[localName] = parentScope.$eval(attr[localName]);
-      },
-
-      bind: function(localName, mode, parentScope, scope, attr) {
-        var getter = $interpolate(attr[localName]);
-        scope.$watch(
-          function() { return getter(parentScope); },
-          function(v) { scope[localName] = v; }
-        );
-      },
-
-      accessor: function(localName, mode, parentScope, scope, attr) {
-        var getter = noop,
-            setter = noop,
-            exp = attr[localName];
-
-        if (exp) {
-          getter = $parse(exp);
-          setter = getter.assign || function() {
-            throw Error("Expression '" + exp + "' not assignable.");
-          };
-        }
-
-        scope[localName] = function(value) {
-          return arguments.length ? setter(parentScope, value) : getter(parentScope);
-        };
-      },
-
-      expression: function(localName, mode, parentScope, scope, attr) {
-        scope[localName] = function(locals) {
-          $parse(attr[localName])(parentScope, locals);
-        };
-      }
-    };
-
     var Attributes = function(element, attr) {
       this.$$element = element;
       this.$attr = attr || {};
@@ -746,9 +708,67 @@ function $CompileProvider($provide) {
         $element = attrs.$$element;
 
         if (newScopeDirective && isObject(newScopeDirective.scope)) {
-          forEach(newScopeDirective.scope, function(mode, name) {
-            (LOCAL_MODE[mode] || wrongMode)(name, mode,
-                scope.$parent || scope, scope, attrs);
+          var LOCAL_REGEXP = /^\s*([@=&])\s*(\w*)\s*$/;
+
+          var parentScope = scope.$parent || scope;
+
+          forEach(newScopeDirective.scope, function(definiton, scopeName) {
+            var match = definiton.match(LOCAL_REGEXP) || [],
+                attrName = match[2]|| scopeName,
+                mode = match[1], // @, =, or &
+                lastValue,
+                parentGet, parentSet;
+
+            switch (mode) {
+
+              case '@': {
+                attrs.$observe(attrName, function(value) {
+                  scope[scopeName] = value;
+                });
+                attrs.$$observers[attrName].$$scope = parentScope;
+                break;
+              }
+
+              case '=': {
+                parentGet = $parse(attrs[attrName]);
+                parentSet = parentGet.assign || function() {
+                  // reset the change, or we will throw this exception on every $digest
+                  lastValue = scope[scopeName] = parentGet(parentScope);
+                  throw Error(NON_ASSIGNABLE_MODEL_EXPRESSION + attrs[attrName] +
+                      ' (directive: ' + newScopeDirective.name + ')');
+                };
+                lastValue = scope[scopeName] = parentGet(parentScope);
+                scope.$watch(function() {
+                  var parentValue = parentGet(parentScope);
+
+                  if (parentValue !== scope[scopeName]) {
+                    // we are out of sync and need to copy
+                    if (parentValue !== lastValue) {
+                      // parent changed and it has precedence
+                      lastValue = scope[scopeName] = parentValue;
+                    } else {
+                      // if the parent can be assigned then do so
+                      parentSet(parentScope, lastValue = scope[scopeName]);
+                    }
+                  }
+                  return parentValue;
+                });
+                break;
+              }
+
+              case '&': {
+                parentGet = $parse(attrs[attrName]);
+                scope[scopeName] = function(locals) {
+                  return parentGet(parentScope, locals);
+                }
+                break;
+              }
+
+              default: {
+                throw Error('Invalid isolate scope definition for directive ' +
+                    newScopeDirective.name + ': ' + definiton);
+              }
+            }
           });
         }
 
@@ -761,12 +781,6 @@ function $CompileProvider($provide) {
               $transclude: boundTranscludeFn
             };
 
-
-            forEach(directive.inject || {}, function(mode, name) {
-              (LOCAL_MODE[mode] || wrongMode)(name, mode,
-                  newScopeDirective ? scope.$parent || scope : scope, locals, attrs);
-            });
-
             controller = directive.controller;
             if (controller == '@') {
               controller = attrs[directive.name];
@@ -1007,9 +1021,10 @@ function $CompileProvider($provide) {
 
           attr[name] = undefined;
           ($$observers[name] || ($$observers[name] = [])).$$inter = true;
-          scope.$watch(interpolateFn, function(value) {
-            attr.$set(name, value);
-          });
+          (attr.$$observers && attr.$$observers[name].$$scope || scope).
+            $watch(interpolateFn, function(value) {
+              attr.$set(name, value);
+            });
         })
       });
     }
diff --git a/src/ng/directive/input.js b/src/ng/directive/input.js
index aa79082b..04af4c2a 100644
--- a/src/ng/directive/input.js
+++ b/src/ng/directive/input.js
@@ -857,8 +857,8 @@ var VALID_CLASS = 'ng-valid',
  * </example>
  *
  */
-var NgModelController = ['$scope', '$exceptionHandler', '$attrs', 'ngModel', '$element',
-    function($scope, $exceptionHandler, $attr, ngModel, $element) {
+var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$parse',
+    function($scope, $exceptionHandler, $attr, $element, $parse) {
   this.$viewValue = Number.NaN;
   this.$modelValue = Number.NaN;
   this.$parsers = [];
@@ -870,6 +870,14 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', 'ngModel', '$e
   this.$invalid = false;
   this.$name = $attr.name;
 
+  var ngModelGet = $parse($attr.ngModel),
+      ngModelSet = ngModelGet.assign;
+
+  if (!ngModelSet) {
+    throw Error(NON_ASSIGNABLE_MODEL_EXPRESSION + $attr.ngModel +
+        ' (' + startingTag($element) + ')');
+  }
+
   /**
    * @ngdoc function
    * @name angular.module.ng.$compileProvider.directive.ngModel.NgModelController#$render
@@ -974,7 +982,7 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', 'ngModel', '$e
 
     if (this.$modelValue !== value) {
       this.$modelValue = value;
-      ngModel(value);
+      ngModelSet($scope, value);
       forEach(this.$viewChangeListeners, function(listener) {
         try {
           listener();
@@ -987,9 +995,7 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', 'ngModel', '$e
 
   // model -> value
   var ctrl = this;
-  $scope.$watch(function() {
-    return ngModel();
-  }, function(value) {
+  $scope.$watch(ngModelGet, function(value) {
 
     // ignore change from view
     if (ctrl.$modelValue === value) return;
@@ -1044,9 +1050,6 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', 'ngModel', '$e
  */
 var ngModelDirective = function() {
   return {
-    inject: {
-      ngModel: 'accessor'
-    },
     require: ['ngModel', '^?form'],
     controller: NgModelController,
     link: function(scope, element, attr, ctrls) {