fix($compile): disallow linking the same element more then once

Previously the following would invoke the elemnet link function multiple
times, causing unknown and potentially buggy results:

    var link = $compile(html);
    link(scope);
    link(scope);

This was always unsupported. Now this throws a multilink error.

Author: jbedard

docs/content/error/$compile/multilink.ngdoc

@@ -0,0 +1,27 @@
+@ngdoc error
+@name $compile:multilink
+@fullName Linking Element Multiple Times
+@description
+
+This error occurs when a single element is linked more then once.
+
+For example, if an element is compiled and linked twice without cloning:
+```
+  var linker = $compile(template);
+  linker($scope); //=> ok
+  linker($scope); //=> multilink error
+```
+
+Linking an element as a clone multiple times is ok:
+```
+  var linker = $compile(template);
+  linker($scope, function() { ... });     //=> ok
+  linker($scope, function() { ... });     //=> ok
+```
+
+However once an element has been linked it can not be re-linked as a clone:
+```
+  var linker = $compile(template);
+  linker($scope);                       //=> ok
+  linker($scope, function() { ... });   //=> multilink error
+```

src/ng/compile.js

@@ -1817,6 +1817,9 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
       compile.$$addScopeClass($compileNodes);
       var namespace = null;
       return function publicLinkFn(scope, cloneConnectFn, options) {
+        if (!$compileNodes) {
+          throw $compileMinErr('multilink', 'This element has already been linked.');
+        }
         assertArg(scope, 'scope');
 
         if (previousCompileContext && previousCompileContext.needsNewScope) {
@@ -1871,6 +1874,10 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
 
         if (cloneConnectFn) cloneConnectFn($linkNode, scope);
         if (compositeLinkFn) compositeLinkFn(scope, $linkNode, $linkNode, parentBoundTranscludeFn);
+
+        if (!cloneConnectFn) {
+          $compileNodes = compositeLinkFn = null;
+        }
         return $linkNode;
       };
     }

test/ng/compileSpec.js

@@ -3631,6 +3631,14 @@ describe('$compile', function() {
         expect(element.text()).toBe('3');
       });
     });
+
+    it('should throw multilink error when linking the same element more then once', function() {
+      var linker = $compile('<div>');
+      linker($rootScope).remove();
+      expect(function() {
+        linker($rootScope);
+      }).toThrowMinErr('$compile', 'multilink', 'This element has already been linked.');
+    });
   });
 
 
@@ -7971,6 +7979,22 @@ describe('$compile', function() {
         });
       });
 
+      it('should throw if a transcluded node is transcluded again', function() {
+        module(function() {
+          directive('trans', valueFn({
+            transclude: true,
+            link: function(scope, element, attr, ctrl, $transclude) {
+              $transclude();
+              $transclude();
+            }
+          }));
+        });
+        inject(function($rootScope, $compile) {
+          expect(function() {
+            $compile('<trans></trans>')($rootScope);
+          }).toThrowMinErr('$compile', 'multilink', 'This element has already been linked.');
+        });
+      });
 
       it('should not leak if two "element" transclusions are on the same element (with debug info)', function() {
         if (jQuery) {
@@ -8113,7 +8137,7 @@ describe('$compile', function() {
                 '</div>' +
               '</div>' +
             '</div>');
-          element = template($rootScope);
+          element = template($rootScope, noop);
           $rootScope.$digest();
           $timeout.flush();
           $httpBackend.flush();
@@ -8123,10 +8147,11 @@ describe('$compile', function() {
           $templateCache.removeAll();
           var destroyedScope = $rootScope.$new();
           destroyedScope.$destroy();
-          var clone = template(destroyedScope);
+          var clone = template(destroyedScope, noop);
           $rootScope.$digest();
           $timeout.flush();
           expect(linkFn).not.toHaveBeenCalled();
+          clone.remove();
         });
       });