Analyzer support for `@factory` methods (linter#253).

pkg/analyzer/lib/src/dart/element/element.dart

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 790fab65fb96714bcd30b54591f33906acc031f5..7c30efe95a4b0dfd65db7df24cbeb25353eed6ac 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -2462,6 +2462,12 @@ class ElementAnnotationImpl implements ElementAnnotation {
   static String _DEPRECATED_VARIABLE_NAME = "deprecated";
 
   /**
+   * The name of the top-level variable used to mark a method as being a
+   * factory.
+   */
+  static String _FACTORY_VARIABLE_NAME = "factory";
+
+  /**
    * The name of the class used to JS annotate an element.
    */
   static String _JS_CLASS_NAME = "JS";
@@ -2560,6 +2566,12 @@ class ElementAnnotationImpl implements ElementAnnotation {
   }
 
   @override
+  bool get isFactory =>
+      element is PropertyAccessorElement &&
+          element.name == _FACTORY_VARIABLE_NAME &&
+          element.library?.name == _META_LIB_NAME;
+
+  @override
   bool get isJS =>
       element is ConstructorElement &&
       element.enclosingElement.name == _JS_CLASS_NAME &&
@@ -2803,6 +2815,16 @@ abstract class ElementImpl implements Element {
   }
 
   @override
+  bool get isFactory {
+    for (ElementAnnotation annotation in metadata) {
+      if (annotation.isFactory) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  @override
   bool get isJS {
     for (ElementAnnotation annotation in metadata) {
       if (annotation.isJS) {
@@ -6482,6 +6504,9 @@ class MultiplyDefinedElementImpl implements MultiplyDefinedElement {
   bool get isDeprecated => false;
 
   @override
+  bool get isFactory => false;
+
+  @override
   bool get isJS => false;
 
   @override