Implement top-level getters.

dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 12 matching lines @@
    */
   Element methodElement;
 }
 
 /**
  * A convenient type alias for some functions that emit keyed values.
  */
 typedef void DefineStubFunction(String invocationName, jsAst.Expression value);
 
 /**
+ * [member] is a field (instance, static, or top level).
+ *
+ * [name] is the field name that the [Namer] has picked for this field's
+ * storage, that is, the JavaScript property name.
+ *
+ * [accessorName] is the name of the accessor. For instance fields this is
+ * mostly the same as [name] except when [member] is shadowing a field in its
+ * superclass.  For other fields, they are rarely the same.
+ *
+ * [needsGetter] and [needsSetter] represent if a getter or a setter
+ * respectively is needed.  There are many factors in this, for example, if the
+ * accessor can be inlined.
+ *
+ * [needsCheckedSetter] indicates that a checked getter is needed, and in this
+ * case, [needsSetter] is always false. [needsCheckedSetter] is only true when
+ * type assertions are enabled (checked mode).
+ */
+typedef void AcceptField(VariableElement member,
+                         String name,
+                         String accessorName,
+                         bool needsGetter,
+                         bool needsSetter,
+                         bool needsCheckedSetter);
+
+/**
  * A data structure for collecting fragments of a class definition.
  */
 class ClassBuilder {
   final List<jsAst.Property> properties = <jsAst.Property>[];
 
   /// Set to true by user if class is indistinguishable from its superclass.
   bool isTrivial = false;
 
   // Has the same signature as [DefineStubFunction].
   void addProperty(String name, jsAst.Expression value) {
@@ skipping 1141 matching lines @@
     for (int i = 1; i <= signature.optionalParameterCount; i++) {
       selectors.add(new Selector(SelectorKind.CALL,
                                  element.name,
                                  element.getLibrary(),
                                  signature.requiredParameterCount + i,
                                  <SourceString>[]));
     }
     return selectors;
   }
 
-  bool instanceFieldNeedsGetter(Element member) {
-    assert(member.isField());
-    if (fieldAccessNeverThrows(member)) return false;
-    return backend.retainGetter(member)
-        || compiler.codegenWorld.hasInvokedGetter(member, compiler);
+  bool fieldNeedsGetter(VariableElement field) {
+    assert(field.isField());
+    if (fieldAccessNeverThrows(field)) return false;
+    return backend.retainGetter(field)
+        || compiler.codegenWorld.hasInvokedGetter(field, compiler);
   }
 
-  bool instanceFieldNeedsSetter(Element member) {
-    assert(member.isField());
-    if (fieldAccessNeverThrows(member)) return false;
-    return (!member.modifiers.isFinalOrConst())
-        && (backend.retainSetter(member)
-            || compiler.codegenWorld.hasInvokedSetter(member, compiler));
+  bool fieldNeedsSetter(VariableElement field) {
+    assert(field.isField());
+    if (fieldAccessNeverThrows(field)) return false;
+    return (!field.modifiers.isFinalOrConst())
+        && (backend.retainSetter(field)
+            || compiler.codegenWorld.hasInvokedSetter(field, compiler));
   }
 
   // We never access a field in a closure (a captured variable) without knowing
   // that it is there.  Therefore we don't need to use a getter (that will throw
   // if the getter method is missing), but can always access the field directly.
-  static bool fieldAccessNeverThrows(Element element) {
-    return element is ClosureFieldElement;
+  static bool fieldAccessNeverThrows(VariableElement field) {
+    return field is ClosureFieldElement;
   }
 
   String compiledFieldName(Element member) {
     assert(member.isField());
     return member.hasFixedBackendName()
         ? member.fixedBackendName()
         : namer.getName(member);
   }
 
   /**
@@ skipping 253 matching lines @@
     for (ClassElement cls in typeChecks) {
       for (TypeCheck check in typeChecks[cls]) {
         result.add(backend.getImplementationClass(cls));
         break;
       }
     }
     return result;
   }
 
   /**
-   * Documentation wanted -- johnniwinther
+   * Calls [addField] for each of the fields of [element].
    *
-   * Invariant: [classElement] must be a declaration element.
+   * [element] must be a [ClassElement] or a [LibraryElement].
+   *
+   * If [element] is a [ClassElement], the static fields of the class are
+   * visited if [visitStatics] is true and the instance fields are visited if
+   * [visitStatics] is false.
+   *
+   * If [element] is a [LibraryElement], [visitStatics] must be true.
+   *
+   * When visiting the instance fields of a class, the fields of its superclass
+   * are also visited if the class is instantiated.
+   *
+   * Invariant: [element] must be a declaration element.
    */
-  void visitClassFields(ClassElement classElement,
-                        bool visitStatics,
-                        void addField(Element member,
-                                      String name,
-                                      String accessorName,
-                                      bool needsGetter,
-                                      bool needsSetter,
-                                      bool needsCheckedSetter)) {
-    assert(invariant(classElement, classElement.isDeclaration));
+  void visitFields(Element element, bool visitStatics, AcceptField f) {
+    assert(invariant(element, element.isDeclaration));
+
+    bool isClass = false;
+    bool isLibrary = false;
+    if (element is ClassElement) {

[ngeoffray, 2013/07/22 08:51:08]

isClass() ?

[ahe, 2013/07/22 12:38:47]

Done.

+      isClass = true;
+    } else if (element is LibraryElement) {

[ngeoffray, 2013/07/22 08:51:08]

isLibrary ?

[ahe, 2013/07/22 12:38:47]

Done.

+      isLibrary = true;
+      assert(invariant(element, visitStatics));
+    } else {
+      throw new SpannableAssertionFailure(
+          element, 'Expected a ClassElement or a LibraryElement.');
+    }
+
     // If the class is never instantiated we still need to set it up for
     // inheritance purposes, but we can simplify its JavaScript constructor.
     bool isInstantiated =
-        compiler.codegenWorld.instantiatedClasses.contains(classElement);
+        compiler.codegenWorld.instantiatedClasses.contains(element);
 
-    void visitField(ClassElement enclosingClass, Element member) {
-      assert(invariant(classElement, member.isDeclaration));
-      LibraryElement library = member.getLibrary();
-      SourceString name = member.name;
-      bool isPrivate = name.isPrivate();
+    void visitField(Element holder, VariableElement field) {
+      assert(invariant(element, field.isDeclaration));
+      SourceString name = field.name;
 
       // Keep track of whether or not we're dealing with a field mixin
       // into a native class.
       bool isMixinNativeField =
-          classElement.isNative() && enclosingClass.isMixinApplication;
+          isClass && element.isNative() && holder.isMixinApplication;
 
       // See if we can dynamically create getters and setters.
-      // We can only generate getters and setters for [classElement] since
+      // We can only generate getters and setters for [element] since
       // the fields of super classes could be overwritten with getters or
       // setters.
       bool needsGetter = false;
       bool needsSetter = false;
       // We need to name shadowed fields differently, so they don't clash with
       // the non-shadowed field.
       bool isShadowed = false;
-      if (isMixinNativeField || identical(enclosingClass, classElement)) {
-        needsGetter = instanceFieldNeedsGetter(member);
-        needsSetter = instanceFieldNeedsSetter(member);
+      if (isLibrary || isMixinNativeField || holder == element) {
+        needsGetter = fieldNeedsGetter(field);
+        needsSetter = fieldNeedsSetter(field);
       } else {
-        isShadowed = classElement.isShadowedByField(member);
+        ClassElement cls = element;
+        isShadowed = cls.isShadowedByField(field);
       }
 
-      if ((isInstantiated && !enclosingClass.isNative())
+      if ((isInstantiated && !holder.isNative())
           || needsGetter
           || needsSetter) {
         String accessorName = isShadowed
-            ? namer.shadowedFieldName(member)
-            : namer.getName(member);
-        String fieldName = member.hasFixedBackendName()
-            ? member.fixedBackendName()
-            : (isMixinNativeField ? member.name.slowToString() : accessorName);
+            ? namer.shadowedFieldName(field)
+            : namer.getName(field);
+        String fieldName = field.hasFixedBackendName()
+            ? field.fixedBackendName()
+            : (isMixinNativeField ? name.slowToString() : accessorName);
         bool needsCheckedSetter = false;
-        if (needsSetter) {
-          if (compiler.enableTypeAssertions
-              && canGenerateCheckedSetter(member)) {
-            needsCheckedSetter = true;
-            needsSetter = false;
-          }
+        if (compiler.enableTypeAssertions && needsSetter

[ngeoffray, 2013/07/22 08:51:08]

nit: new line for needsSetter

[ahe, 2013/07/22 12:38:47]

Done.

+            && canGenerateCheckedSetter(field)) {
+          needsCheckedSetter = true;
+          needsSetter = false;
         }
         // Getters and setters with suffixes will be generated dynamically.
-        addField(member,
-                 fieldName,
-                 accessorName,
-                 needsGetter,
-                 needsSetter,
-                 needsCheckedSetter);
+        f(field, fieldName, accessorName, needsGetter, needsSetter,
+          needsCheckedSetter);
       }
     }
 
-    if (visitStatics) {
-      classElement.implementation.forEachStaticField(visitField);
+    if (isLibrary) {
+      LibraryElement library = element;
+      library.implementation.forEachLocalMember((Element member) {
+        if (member.isField()) visitField(library, member);
+      });
+    } else if (visitStatics) {
+      ClassElement cls = element;
+      cls.implementation.forEachStaticField(visitField);
     } else {
+      ClassElement cls = element;
       // TODO(kasperl): We should make sure to only emit one version of
       // overridden fields. Right now, we rely on the ordering so the
       // fields pulled in from mixins are replaced with the fields from
       // the class definition.
 
       // If a class is not instantiated then we add the field just so we can
       // generate the field getter/setter dynamically. Since this is only
-      // allowed on fields that are in [classElement] we don't need to visit
+      // allowed on fields that are in [element] we don't need to visit
       // superclasses for non-instantiated classes.
-      classElement.implementation.forEachInstanceField(
-          visitField,
-          includeSuperAndInjectedMembers: isInstantiated);
+      cls.implementation.forEachInstanceField(
+          visitField, includeSuperAndInjectedMembers: isInstantiated);
     }
   }
 
   void generateGetter(Element member, String fieldName, String accessorName,
                       ClassBuilder builder) {
     String getterName = namer.getterNameFromAccessorName(accessorName);
     String receiver = backend.isInterceptorClass(member.getEnclosingClass())
         ? 'receiver' : 'this';
     List<String> args = backend.isInterceptedMethod(member)
         ? ['receiver']
         : [];
     builder.addProperty(getterName,
         js.fun(args, js.return_(js('$receiver.$fieldName'))));
   }
 
   void generateSetter(Element member, String fieldName, String accessorName,
                       ClassBuilder builder) {
     String setterName = namer.setterNameFromAccessorName(accessorName);
     String receiver = backend.isInterceptorClass(member.getEnclosingClass())
         ? 'receiver' : 'this';
     List<String> args = backend.isInterceptedMethod(member)
         ? ['receiver', 'v']
         : ['v'];
     builder.addProperty(setterName,
         js.fun(args, js('$receiver.$fieldName = v')));
   }
 
-  bool canGenerateCheckedSetter(Element member) {
+  bool canGenerateCheckedSetter(VariableElement field) {
     // We never generate accessors for top-level/static fields.
-    if (!member.isInstanceMember()) return false;
-    DartType type = member.computeType(compiler).unalias(compiler);
+    if (!field.isInstanceMember()) return false;
+    DartType type = field.computeType(compiler).unalias(compiler);
     if (type.element.isTypeVariable() ||
-        (type is FunctionType && type.containsTypeVariables) || 
+        (type is FunctionType && type.containsTypeVariables) ||
         type.element == compiler.dynamicClass ||
         type.element == compiler.objectClass) {
       // TODO(ngeoffray): Support type checks on type parameters.
       return false;
     }
     return true;
   }
 
   void generateCheckedSetter(Element member,
                              String fieldName,
@@ skipping 50 matching lines @@
     } else {
       previousName = mangledGlobalFieldNames.putIfAbsent(
           accessorName,
           () => memberName);
     }
     assert(invariant(member, previousName == memberName,
                      message: '$previousName != ${memberName}'));
   }
 
   /// Returns `true` if fields added.
-  bool emitClassFields(ClassElement classElement,
-                       ClassBuilder builder,
-                       String superName,
-                       { bool classIsNative: false,
-                         bool emitStatics: false }) {
+  bool emitFields(Element element,
+                  ClassBuilder builder,
+                  String superName,
+                  { bool classIsNative: false,
+                    bool emitStatics: false }) {
+    bool isClass = false;
+    bool isLibrary = false;
+    if (element is ClassElement) {

[ngeoffray, 2013/07/22 08:51:08]

isClass

[ahe, 2013/07/22 12:38:47]

Done.

+      isClass = true;
+    } else if (element is LibraryElement) {

[ngeoffray, 2013/07/22 08:51:08]

isLibrary

[ahe, 2013/07/22 12:38:47]

Done.

+      isLibrary = false;
+      assert(invariant(element, emitStatics));
+    } else {
+      throw new SpannableAssertionFailure(
+          element, 'Must be a ClassElement or a LibraryElement');
+    }
     StringBuffer buffer = new StringBuffer();
     if (emitStatics) {
-      assert(invariant(classElement, superName == null, message: superName));
+      assert(invariant(element, superName == null, message: superName));
     } else {
-      assert(invariant(classElement, superName != null));
+      assert(invariant(element, superName != null));
       String nativeName =
-          namer.getPrimitiveInterceptorRuntimeName(classElement);
+          namer.getPrimitiveInterceptorRuntimeName(element);
       if (nativeName != null) {
         buffer.write('$nativeName/');
       }
       buffer.write('$superName;');
     }
     int bufferClassLength = buffer.length;
 
     String separator = '';
 
     var fieldMetadata = [];
     bool hasMetadata = false;
 
-    visitClassFields(classElement, emitStatics,
-                     (Element member,
-                      String name,
-                      String accessorName,
-                      bool needsGetter,
-                      bool needsSetter,
-                      bool needsCheckedSetter) {
+    visitFields(element, emitStatics,
+                (VariableElement field,
+                 String name,
+                 String accessorName,
+                 bool needsGetter,
+                 bool needsSetter,
+                 bool needsCheckedSetter) {
       // Ignore needsCheckedSetter - that is handled below.
       bool needsAccessor = (needsGetter || needsSetter);
       // We need to output the fields for non-native classes so we can auto-
       // generate the constructor.  For native classes there are no
       // constructors, so we don't need the fields unless we are generating
       // accessors at runtime.
       if (!classIsNative || needsAccessor) {
         buffer.write(separator);
         separator = ',';
-        var metadata = buildMetadataFunction(member);
+        var metadata = buildMetadataFunction(field);
         if (metadata != null) {
           hasMetadata = true;
         } else {
           metadata = new jsAst.LiteralNull();
         }
         fieldMetadata.add(metadata);
-        recordMangledField(member, accessorName, member.name.slowToString());
+        recordMangledField(field, accessorName, field.name.slowToString());
         if (!needsAccessor) {
           // Emit field for constructor generation.
           assert(!classIsNative);
           buffer.write(name);
         } else {
           // Emit (possibly renaming) field name so we can add accessors at
           // runtime.
           buffer.write(accessorName);
           if (name != accessorName) {
             buffer.write(':$name');
             // Only the native classes can have renaming accessors.
             assert(classIsNative);
           }
 
           int getterCode = 0;
           if (needsGetter) {
-            // 01:  function() { return this.field; }
-            // 10:  function(receiver) { return receiver.field; }
-            // 11:  function(receiver) { return this.field; }
-            getterCode += backend.fieldHasInterceptedGetter(member) ? 2 : 0;
-            getterCode += backend.isInterceptorClass(classElement) ? 0 : 1;
-            // TODO(sra): 'isInterceptorClass' might not be the correct test for
-            // methods forced to use the interceptor convention because the
-            // method's class was elsewhere mixed-in to an interceptor.
-            assert(!member.isInstanceMember() || getterCode != 0);
+            if (field.isInstanceMember()) {
+              // 01:  function() { return this.field; }
+              // 10:  function(receiver) { return receiver.field; }
+              // 11:  function(receiver) { return this.field; }
+              getterCode += backend.fieldHasInterceptedGetter(field) ? 2 : 0;
+              getterCode += backend.isInterceptorClass(element) ? 0 : 1;
+              // TODO(sra): 'isInterceptorClass' might not be the correct test for

[ngeoffray, 2013/07/22 08:51:08]

line too long

[ahe, 2013/07/22 12:38:47]

Done.

+              // methods forced to use the interceptor convention because the
+              // method's class was elsewhere mixed-in to an interceptor.
+              assert(!field.isInstanceMember() || getterCode != 0);
+            } else {
+              getterCode = 1;
+            }
           }
           int setterCode = 0;
           if (needsSetter) {
-            // 01:  function(value) { this.field = value; }
-            // 10:  function(receiver, value) { receiver.field = value; }
-            // 11:  function(receiver, value) { this.field = value; }
-            setterCode += backend.fieldHasInterceptedSetter(member) ? 2 : 0;
-            setterCode += backend.isInterceptorClass(classElement) ? 0 : 1;
-            assert(!member.isInstanceMember() || setterCode != 0);
+            if (field.isInstanceMember()) {
+              // 01:  function(value) { this.field = value; }
+              // 10:  function(receiver, value) { receiver.field = value; }
+              // 11:  function(receiver, value) { this.field = value; }
+              setterCode += backend.fieldHasInterceptedSetter(field) ? 2 : 0;
+              setterCode += backend.isInterceptorClass(element) ? 0 : 1;
+              assert(!field.isInstanceMember() || setterCode != 0);
+            } else {
+              setterCode = 1;
+            }
           }
           int code = getterCode + (setterCode << 2);
           if (code == 0) {
             compiler.reportInternalError(
-                member, 'Internal error: code is 0 ($classElement/$member)');
+                field, 'Internal error: code is 0 ($element/$field)');
           } else {
             buffer.write(FIELD_CODE_CHARACTERS[code - FIRST_FIELD_CODE]);
           }
         }
       }
     });
 
     bool fieldsAdded = buffer.length > bufferClassLength;
     String compactClassData = buffer.toString();
     jsAst.Expression classDataNode = js.string(compactClassData);
     if (hasMetadata) {
       fieldMetadata.insert(0, classDataNode);
       classDataNode = new jsAst.ArrayInitializer.from(fieldMetadata);
     }
     builder.addProperty('', classDataNode);
     return fieldsAdded;
   }
 
   void emitClassGettersSetters(ClassElement classElement,
                                ClassBuilder builder) {
 
-    visitClassFields(classElement, false,
-                     (Element member,
-                      String name,
-                      String accessorName,
-                      bool needsGetter,
-                      bool needsSetter,
-                      bool needsCheckedSetter) {
+    visitFields(classElement, false,
+                (VariableElement member,
+                 String name,
+                 String accessorName,
+                 bool needsGetter,
+                 bool needsSetter,
+                 bool needsCheckedSetter) {
       compiler.withCurrentElement(member, () {
         if (needsCheckedSetter) {
           assert(!needsSetter);
           generateCheckedSetter(member, name, accessorName, builder);
         }
         if (!getterAndSetterCanBeImplementedByFieldSpec) {
           if (needsGetter) {
             generateGetter(member, name, accessorName, builder);
           }
           if (needsSetter) {
@@ skipping 27 matching lines @@
     if (classElement.isMixinApplication) {
       String mixinName = namer.getName(computeMixinClass(classElement));
       superName = '$superName+$mixinName';
       needsMixinSupport = true;
     }
 
     ClassBuilder builder = new ClassBuilder();
     emitClassConstructor(classElement, builder);
     emitSuper(superName, builder);
     emitRuntimeName(runtimeName, builder);
-    emitClassFields(classElement, builder, superName);
+    emitFields(classElement, builder, superName);
     emitClassGettersSetters(classElement, builder);
     if (!classElement.isMixinApplication) {
       emitInstanceMembers(classElement, builder);
     }
     emitIsTests(classElement, builder);
 
     emitClassBuilderWithReflectionData(
         className, classElement, builder, buffer);
   }
 
   void emitClassBuilderWithReflectionData(String className,
                                           ClassElement classElement,
                                           ClassBuilder builder,
                                           CodeBuffer buffer) {
     var metadata = buildMetadataFunction(classElement);
     if (metadata != null) {
       builder.addProperty("@", metadata);
     }
 
     List<CodeBuffer> classBuffers = elementBuffers[classElement];
     if (classBuffers == null) {
       classBuffers = [];
     } else {
       elementBuffers.remove(classElement);
     }
     CodeBuffer statics = new CodeBuffer();
     statics.write('{$n');
     bool hasStatics = false;
     ClassBuilder staticsBuilder = new ClassBuilder();
-    if (emitClassFields(
-            classElement, staticsBuilder, null, emitStatics: true)) {
+    if (emitFields(classElement, staticsBuilder, null, emitStatics: true)) {
       hasStatics = true;
       statics.write('"":$_');
       statics.write(
           jsAst.prettyPrint(staticsBuilder.properties.single.value, compiler));
       statics.write(',$n');
     }
     for (CodeBuffer classBuffer in classBuffers) {
       // TODO(ahe): What about deferred?
       if (classBuffer != null) {
         hasStatics = true;
@@ skipping 1671 matching lines @@
       // After this assignment we will produce invalid JavaScript code if we use
       // the classesCollector variable.
       classesCollector = 'classesCollector should not be used from now on';
 
       if (!elementBuffers.isEmpty) {
         var oldClassesCollector = classesCollector;
         classesCollector = r"$$";
         if (compiler.enableMinification) {
           mainBuffer.write(';');
         }
+
+        for (Element element in elementBuffers.keys) {

[ngeoffray, 2013/07/22 08:51:08]

Don't you have to check if you need to emit them?

[ahe, 2013/07/22 09:45:30]

No.  Stuff in this map needs to be emitted.

However, a library with fields only will not be in the map. I'll address this in
another CL. 

+          if (element is LibraryElement) {

[ngeoffray, 2013/07/22 08:51:08]

isLibrary

[ahe, 2013/07/22 12:38:47]

Done.

+            LibraryElement library = element;
+            ClassBuilder builder = new ClassBuilder();
+            if (emitFields(library, builder, null, emitStatics: true)) {
+              List<CodeBuffer> buffers = elementBuffers[library];
+              var buffer = buffers[0];
+              if (buffer == null) {
+                buffers[0] = buffer = new CodeBuffer();
+              }
+              for (jsAst.Property property in builder.properties) {
+                if (!buffer.isEmpty) buffer.write(',$n');
+                buffer.addBuffer(jsAst.prettyPrint(property, compiler));
+              }
+            }
+          }
+        }
+
         if (!mangledFieldNames.isEmpty) {
           var keys = mangledFieldNames.keys.toList();
           keys.sort();
           var properties = [];
           for (String key in keys) {
             var value = js.string('${mangledFieldNames[key]}');
             properties.add(new jsAst.Property(js.string(key), value));
           }
           var map = new jsAst.ObjectInitializer(properties);
           mainBuffer.write(
@@ skipping 276 matching lines @@
   var mangledNames = init.mangledNames;
   var mangledGlobalNames = init.mangledGlobalNames;
   var hasOwnProperty = Object.prototype.hasOwnProperty;
   var length = reflectionData.length;
   for (var i = 0; i < length; i++) {
     var data = reflectionData[i];
     var name = data[0];
     var uri = data[1];
     var metadata = data[2];
     var descriptor = data[3];
+    var fields = descriptor && descriptor[""];
     var classes = [];
     var functions = [];
     function processStatics(descriptor) {
       for (var property in descriptor) {
         if (!hasOwnProperty.call(descriptor, property)) continue;
         if (property === "") continue;
         var element = descriptor[property];
         var firstChar = property.substring(0, 1);
         var previousProperty;
         if (firstChar === "+") {
@@ skipping 20 matching lines @@
             } else {
               newDesc[previousProp = prop] = element[prop];
             }
           }
           $classesCollector[property] = newDesc;
           classes.push(property);
         }
       }
     }
     processStatics(descriptor);
-    libraries.push([name, uri, classes, functions, metadata]);
+    libraries.push([name, uri, classes, functions, metadata, fields]);
   }
 })''';
   }
 }
 
 const String GENERATED_BY = """
 // Generated by dart2js, the Dart to JavaScript compiler.
 """;
 
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;