super and this in compile-time constants.

frog/leg/compile_time_constants.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.
 
 class Constant implements Hashable {
   const Constant();
 
   bool isNull() => false;
   bool isBool() => false;
   bool isTrue() => false;
@@ skipping 663 matching lines @@
 class CompileTimeConstantEvaluator extends AbstractVisitor {
   final ConstantHandler constantHandler;
   final TreeElements elements;
   final Compiler compiler;
   final Map<Element, Constant> definitions = null;
 
   CompileTimeConstantEvaluator(this.constantHandler,
                                this.elements,
                                this.compiler);
 
   CompileTimeConstantEvaluator.insideConstructor(this.constantHandler,

[ngeoffray, 2012/03/26 07:38:31]

Because you can fetch constantHandler from the compiler, I would not pass it as
a parameter.

[floitsch, 2012/03/27 00:52:50]

Done.

                                                  this.elements,
-                                                 this.compiler,
-                                                 this.definitions);
+                                                 this.compiler)
+      : definitions = new Map<Element, Constant>();
 
   bool insideConstructor() => definitions !== null;
 
   Constant evaluate(Node node) {
     return node.accept(this);
   }
 
   visitNode(Node node) {
     compiler.unimplemented("CompileTimeConstantEvaluator", node: node);
   }
@@ skipping 228 matching lines @@
       if (folded === null) error(send);
       return folded;
     }
     return super.visitSend(send);
   }
 
   visitSendSet(SendSet node) {
     error(node);
   }
 
-  Constant visitNewExpression(NewExpression node) {
-    Element currentElement = compiler.currentElement;
+  /** Returns the list of constants that are passed to the constructor. */
+  List<Constant> evaluateConstructorArguments(Send send,
+                                              FunctionElement constructor) {
+    FunctionParameters parameters = constructor.computeParameters(compiler);
+    if (send.arguments.isEmpty() && parameters.parameterCount == 0) {

[ngeoffray, 2012/03/26 07:38:31]

Is that premature optimization? I would really get rid of this shortcut, it
should be handled by addSendArgumentsToList.

[ahe, 2012/03/26 08:03:25]

Note that these kind of hacks are not necessary if you use Link. It is designed
to work well in exactly these cases.

[floitsch, 2012/03/27 00:52:50]

Done.

+      return const <Constant>[];
+    }
+    List<Constant> arguments = <Constant>[];
+    Selector selector = elements.getSelector(send);
 
-    void assignArgumentsToParameters(
-        FunctionParameters parameters,
-        Map<Element, Constant> constructorDefinitions,
-        Map<Element, Constant> fieldValues) {
-      Send send = node.send;
-      if (send.arguments.isEmpty() && parameters.parameterCount == 0) return;
-      List<Constant> arguments = <Constant>[];
-      Selector selector = elements.getSelector(send);
+    Function compileArgument = evaluate;

[floitsch, 2012/03/23 23:15:57]

The VM has/had a bug here (see previous uploads), but Regis is working on a fix
right now. Normally he should commit before me.

[floitsch, 2012/03/27 00:52:50]

Fix has been committed.

+    Function compileConstant = compiler.compileVariable;
+    bool succeeded = selector.addSendArgumentsToList(
+        send, arguments, parameters, compileArgument, compileConstant);
+    if (!succeeded) error(send);
+    return arguments;
+  }
 
-      Function compileArgument = evaluate;
-      Function compileConstant = constantHandler.compileVariable;
-      bool succeeded = selector.addSendArgumentsToList(
-          send, arguments, parameters, compileArgument, compileConstant);
-      if (!succeeded) error(node);
+  /**
+   * Given the arguments (a list of constants) assigns the to the parameters,

[ngeoffray, 2012/03/26 07:38:31]

the to the -> ?

[floitsch, 2012/03/27 00:52:50]

Done.

+   * updating the definitions map. If the constructor has field-initializer
+   * parameters (like [:this.x:]), also updates the [fieldValues] map.
+   */ 
+  void assignConstructorArgumentsToParameters(
+      FunctionElement constructor, List<Constant> arguments,

[ngeoffray, 2012/03/26 07:38:31]

one argument per line please

[floitsch, 2012/03/27 00:52:50]

Done.

+      Map<Element, Constant> fieldValues) {
+    // Assign arguments to parameters.
+    FunctionParameters parameters = constructor.computeParameters(compiler);
+    int index = 0;
+    parameters.forEachParameter((Element parameter) {
+      Constant argument = arguments[index++];
+      definitions[parameter] = argument;
+      if (parameter.kind == ElementKind.FIELD_PARAMETER) {
+        FieldParameterElement fieldParameterElement = parameter;
+        fieldValues[fieldParameterElement.fieldElement] = argument;
+      }
+    });    
+  }
 
-      int index = 0;
-      parameters.forEachParameter((Element parameter) {
-        Constant argument = arguments[index++];
-        constructorDefinitions[parameter] = argument;
-        if (parameter.kind == ElementKind.FIELD_PARAMETER) {
-          FieldParameterElement fieldParameterElement = parameter;
-          fieldValues[fieldParameterElement.fieldElement] = argument;
-        }
-      });
+  /**
+   * Runs through the initializers of the given [constructor] and updates
+   * the [fieldValues] map.
+   *
+   * The [executedConstructors] set is used to detect cycles in redirection
+   * constructors.
+   */
+  void evaluateConstructorInitializers(
+      FunctionElement constructor,
+      Set<FunctionElement> executedConstructors,
+      Map<Element, Constant> fieldValues) {
+
+    void evaluateSuperOrRedirectSend(FunctionElement targetConstructor,
+                                     List<Constant> targetArguments) {
+      compiler.withCurrentElement(targetConstructor, () {
+        evaluateConstructorFieldValues(
+            targetConstructor, targetArguments, executedConstructors,
+            fieldValues);
+      });      
     }
 
-    void compileInitializers(Link<Node> initializers,
-                             CompileTimeConstantEvaluator evaluator,
-                             TreeElements constructorElements,
-                             Map<Element, Constant> constructorDefinitions,
-                             Map<Element, Constant> fieldValues) {
-      for (Link<Node> link = initializers; !link.isEmpty(); link = link.tail) {
+    FunctionExpression functionNode = constructor.parseNode(compiler);
+    NodeList initializerList = functionNode.initializers;
+
+    bool foundSuperOrRedirect = false;
+
+    if (initializerList !== null) {
+      for (Link<Node> link = initializerList.nodes;
+           !link.isEmpty();
+           link = link.tail) {
         assert(link.head is Send);
         if (link.head is !SendSet) {
           // A super initializer or constructor redirection.
           Send call = link.head;
-          assert(Initializers.isSuperConstructorCall(call) ||
-                 Initializers.isConstructorRedirect(call));
-          compiler.unimplemented("ConstantHandler with this or super",
-                                 node: call);
+          FunctionElement targetConstructor = elements[call];
+          List<Constant> targetArguments =
+              evaluateConstructorArguments(call, targetConstructor);
+          evaluateSuperOrRedirectSend(targetConstructor, targetArguments);
+          foundSuperOrRedirect = true;
         } else {
           // A field initializer.
           SendSet init = link.head;
-          Link<Node> arguments = init.arguments;
-          assert(!arguments.isEmpty() && arguments.tail.isEmpty());
-          Constant fieldValue = evaluator.evaluate(arguments.head);
-          fieldValues[constructorElements[init]] = fieldValue;
+          Link<Node> initArguments = init.arguments;
+          assert(!initArguments.isEmpty() && initArguments.tail.isEmpty());
+          Constant fieldValue = evaluate(initArguments.head);
+          fieldValues[elements[init]] = fieldValue;
         }
       }
     }
 
+    if (!foundSuperOrRedirect) {
+      // No super initializer found. Try to find the default constructor if
+      // the class is not Object.
+      ClassElement enclosingClass = constructor.enclosingElement;
+      ClassElement superClass = enclosingClass.superclass;
+      if (enclosingClass != compiler.objectClass) {
+        assert(superClass !== null);
+        assert(superClass.isResolved);
+        FunctionElement targetConstructor =
+            superClass.lookupConstructor(superClass.name);
+        if (targetConstructor === null) {
+          compiler.internalError("no default constructor available");
+        }
+        evaluateSuperOrRedirectSend(targetConstructor, const <Constant>[]);
+      }
+    }
+  }
+
+  /**
+   * Simulates the execution of the given [constructor] with the given
+   * [arguments] to obtain the field values that need to be passed to the
+   * native JavaScript constructor.
+   *
+   * The [executedConstructors] set is used to detect cycles in redirection
+   * constructors.

[ngeoffray, 2012/03/26 07:38:31]

Having to also check it here is quite annoying. We're not checking it in the
codegen, so I don't think we should check it here either. The resolver should
handle it.

[floitsch, 2012/03/27 00:52:50]

You are right. This is already handled by the resolver. Great.
done.

+   */
+  void evaluateConstructorFieldValues(FunctionElement constructor,
+                                      List<Constant> arguments,
+                                      Set<FunctionElement> executedConstructors,
+                                      Map<Element, Constant> fieldValues) {
+    compiler.withCurrentElement(constructor, () {
+      if (executedConstructors.contains(constructor)) {
+        MessageKind kind = MessageKind.REDIRECTING_CONSTRUCTOR_CYCLE;
+        compiler.reportError(constructor.parseNode(compiler),
+                             new CompileTimeConstantError(kind, const []));
+      }
+      executedConstructors.add(constructor);
+
+      TreeElements constructorElements =
+          compiler.resolver.resolveMethodElement(constructor);
+      CompileTimeConstantEvaluator evaluator =
+          new CompileTimeConstantEvaluator.insideConstructor(
+              constantHandler, constructorElements, compiler);
+
+      evaluator.assignConstructorArgumentsToParameters(
+          constructor, arguments, fieldValues);
+      evaluator.evaluateConstructorInitializers(
+          constructor, executedConstructors, fieldValues);
+    });
+  }
+
+  Constant visitNewExpression(NewExpression node) {
     List<Constant> buildJsNewArguments(ClassElement classElement,
                                        Map<Element, Constant> fieldValues) {

[ngeoffray, 2012/03/26 07:38:31]

I think it would be easier to read if this function was not local.

[floitsch, 2012/03/27 00:52:50]

Done.

       List<Constant> jsNewArguments = <Constant>[];
-      for (Element member in classElement.members) {
-        if (member.isInstanceMember() && member.kind == ElementKind.FIELD) {
-          Constant fieldValue = fieldValues[member];
-          if (fieldValue === null) {
-            // Use the default value.
-            fieldValue = constantHandler.compileVariable(member);
+      // TODO(floitsch): share this code with the emitter, so that we don't
+      // need to care about the order of fields here.
+      while (classElement != compiler.objectClass) {
+        for (Element member in classElement.members) {
+          if (member.isInstanceMember() && member.kind == ElementKind.FIELD) {
+            Constant fieldValue = fieldValues[member];
+            if (fieldValue === null) {
+              // Use the default value.
+              fieldValue = constantHandler.compileVariable(member);
+            }
+            jsNewArguments.add(fieldValue);
           }
-          jsNewArguments.add(fieldValue);
         }
-      }
-      if (classElement.superclass != compiler.coreLibrary.find(Types.OBJECT)) {
-        compiler.withCurrentElement(currentElement, () {
-          compiler.unimplemented("ConstantHandler with super", node: node);
-        });
-      }
+        classElement = classElement.superclass;
+      } 
       return jsNewArguments;
     }
 
     if (!node.isConst()) error(node);
 
     FunctionElement constructor = elements[node.send];
-    TreeElements constructorElements =
-        compiler.resolver.resolveMethodElement(constructor);
-    if (constructor != constructor.defaultImplementation) {
+    ClassElement classElement = constructor.enclosingElement;
+    if (classElement.isInterface()) {
+      compiler.resolver.resolveMethodElement(constructor);
       constructor = constructor.defaultImplementation;
-      constructorElements =
-          compiler.resolver.resolveMethodElement(constructor);
+      classElement = constructor.enclosingElement;
     }
 
     List<Constant> jsNewArguments;
-    ClassElement classElement = constructor.enclosingElement;
     compiler.withCurrentElement(constructor, () {
-      FunctionExpression functionNode = constructor.parseNode(compiler);
-      NodeList initializerList = functionNode.initializers;
-      FunctionParameters parameters = constructor.computeParameters(compiler);
-
+      // We use a set to detect cycles in redirection constructors.
+      Set<FunctionElement> executedConstructors = new Set<FunctionElement>();
       Map<Element, Constant> fieldValues = new Map<Element, Constant>();

[ngeoffray, 2012/03/26 07:38:31]

Would it make sense to have an abstraction for a constructor evaluating itself?
Something whose API would look like:

ConstructorEvaluator evaluator = new ConstructorEvaluator(constructor,
compiler);

evaluator.evaluate(node.send); // or evaluator.evaluate(constants)

The ConstructorEvaluator class would contain the map of fieldValues, that this
method just needs to fetch.

Also, you would create a ConstructorEvaluator for each this redirect or super
call.

[floitsch, 2012/03/27 00:52:50]

Made ConstructorEvaluator a subclass.

-      Map<Element, Constant> constructorDefinitions =
-          new Map<Element, Constant>();
-
-      assignArgumentsToParameters(parameters, constructorDefinitions,
-                                  fieldValues);
-      CompileTimeConstantEvaluator initializerEvaluator =
-          new CompileTimeConstantEvaluator.insideConstructor(
-              constantHandler, constructorElements, compiler,
-              constructorDefinitions);
-      if (initializerList !== null) {
-        Link<Node> initializers = functionNode.initializers.nodes;
-        compileInitializers(initializers,
-                            initializerEvaluator,
-                            constructorElements,
-                            constructorDefinitions,
-                            fieldValues);
-      }
+      List<Constant> arguments =
+          evaluateConstructorArguments(node.send, constructor);
+      evaluateConstructorFieldValues(
+          constructor, arguments, executedConstructors, fieldValues);
       jsNewArguments = buildJsNewArguments(classElement, fieldValues);
     });
 
-
     compiler.registerInstantiatedClass(classElement);
     // TODO(floitsch): take generic types into account.
     Type type = classElement.computeType(compiler);
     Constant constant = new ConstructedConstant(type, jsNewArguments);
     constantHandler.registerCompileTimeConstant(constant);
     return constant;
   }
 
   error(Node node) {
     // TODO(floitsch): get the list of constants that are currently compiled
     // and present some kind of stack-trace.
     MessageKind kind = MessageKind.NOT_A_COMPILE_TIME_CONSTANT;
     compiler.reportError(node, new CompileTimeConstantError(kind, const []));
   }
 }