Implement support for static accessors

pkg/kernel/lib/interpreter/interpreter.dart

 // Copyright (c) 2017, 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.
 library kernel.interpreter;
 
 import '../ast.dart';
 import '../ast.dart' as ast show Class;
 
 import '../log.dart';
 export '../log.dart';
 
 class NotImplemented {
   String message;
 
   NotImplemented(this.message);
 
   String toString() => message;
 }
 
 class Interpreter {
   Program program;
   StatementExecuter visitor = new StatementExecuter();
 
+  static MainEnvironment mainEnvironment = new MainEnvironment();
+
   Interpreter(this.program);
 
   void run() {
     assert(program.libraries.isEmpty);
     Procedure mainMethod = program.mainMethod;
 
     if (mainMethod == null) return;
 
     Statement statementBlock = mainMethod.function.body;
     ExecConfiguration configuration = new ExecConfiguration(
@@ skipping 16 matching lines @@
   EnvironmentLocation(this.environment);
 }
 
 class Binding {
   final VariableDeclaration variable;
   final Location location;
 
   Binding(this.variable, this.location);
 }
 
+class MainEnvironment {
+  Map<Member, Location> _staticFields = <Member, Location>{};
+
+  bool contains(Member member) => _staticFields[member] != null;
+
+  Value lookup(Member member) {
+    assert(contains(member));
+    return _staticFields[member].value;
+  }
+
+  void update(Member member, Value value) {

[Dmitry Stefantsov, 2017/08/16 08:25:39]

I would add a comment that [MainEnvironment] instances represent environments
and are immutable, and [update] is used only to initially construct such an
environment and is not used during program execution.

+    if (_staticFields[member] == null) {
+      _staticFields[member] = new Location(value);
+    } else {
+      _staticFields[member].value = value;
+    }
+  }
+}
+
 class Environment {
   final List<Binding> bindings = <Binding>[];
   final Environment parent;
 
   Value get thisInstance {
     return containsThis()
         ? lookupThis().value
         : throw "Invalid reference to 'this' expression";
   }
 
@@ skipping 97 matching lines @@
         node.receiver, config.environment, config.exceptionComponents, cont);
   }
 
   Configuration visitPropertySet(PropertySet node, EvalConfiguration config) {
     var cont = new PropertySetEK(node.value, node.name, config.environment,
         config.exceptionComponents, config.continuation);
     return new EvalConfiguration(
         node.receiver, config.environment, config.exceptionComponents, cont);
   }
 
-  Configuration visitStaticGet(StaticGet node, EvalConfiguration config) =>
-      defaultExpression(node, config);
-  Configuration visitStaticSet(StaticSet node, EvalConfiguration config) =>
-      defaultExpression(node, config);
+  Configuration visitStaticGet(StaticGet node, EvalConfiguration config) {
+    Member member = node.target;
+
+    if (member is Procedure && !member.isAccessor) {
+      // Create a closure for the method tear off.
+      var v = new FunctionValue(
+          member.function, new EnvironmentLocation(new Environment.empty()));
+      return new ValuePassingConfiguration(config.continuation, v);
+    }
+
+    if (member is Procedure && member.isGetter) {
+      // Execute the body of the getter.
+      var state = new State.initial()
+          .withReturnContinuation(config.continuation)
+          .withContinuation(new ExitSK(config.continuation, Value.nullInstance))
+          .withException(config.exceptionComponents);
+      return new ExecConfiguration(
+          member.function.body, new Environment.empty(), state);
+    }
+
+    assert(member is Field);
+    if (Interpreter.mainEnvironment.contains(member)) {

[Dmitry Stefantsov, 2017/08/16 08:25:39]

I would use a special value to indicate that the static field didn't received a
value yet, as written in the spec.  In this case [contains] should be rewritten
accordingly.

+      // Read the value for the member in the main environment.
+      return new ValuePassingConfiguration(
+          config.continuation, Interpreter.mainEnvironment.lookup(member));
+    }
+
+    // Otherwise, the static field is accessed for the first time.
+    // We store `Value.nullInstance` if there the field doesn't have an
+    // initializer.
+    if ((member as Field).initializer == null) {
+      Interpreter.mainEnvironment.update(member, Value.nullInstance);

[Dmitry Stefantsov, 2017/08/16 08:25:39]

If the special value for uninitialized variables had been used, we would be able
to avoid mutating environments during program execution.

+      return new ValuePassingConfiguration(
+          config.continuation, Value.nullInstance);
+    }
+
+    // The initializer expression is evaluated otherwise.
+    var cont = new StaticSetEK(member, config.continuation);
+    return new EvalConfiguration((member as Field).initializer,
+        new Environment.empty(), config.exceptionComponents, cont);
+  }
+
+  Configuration visitStaticSet(StaticSet node, EvalConfiguration config) {
+    Member member = node.target;
+    ExpressionContinuation cont;
+
+    if (member is Procedure) {
+      assert(member.isSetter);
+      cont = new StaticSetterEK(
+          member.function, config.exceptionComponents, config.continuation);
+    } else {
+      assert(member is Field);
+      cont = new StaticSetEK(member, config.continuation);
+    }
+
+    return new EvalConfiguration(
+        node.value, config.environment, config.exceptionComponents, cont);
+  }
 
   Configuration visitStaticInvocation(
       StaticInvocation node, EvalConfiguration config) {
     if ('print' == node.name.toString()) {
       var cont = new PrintEK(config.continuation);
       return new EvalConfiguration(node.arguments.positional.first,
           config.environment, config.exceptionComponents, cont);
     } else {
       log.info('static-invocation-${node.target.name.toString()}\n');
 
@@ skipping 231 matching lines @@
 }
 
 /// Configuration for execution of a [Statement].
 class ExecConfiguration extends Configuration {
   final Statement currentStatement;
   final Environment environment;
   final State state;
 
   ExecConfiguration(this.currentStatement, this.environment, this.state);
 
-  Configuration step(StatementExecuter executer) =>
-      executer.exec(currentStatement, this);
+  Configuration step(StatementExecuter executer) {
+    return executer.exec(currentStatement, this);
+  }
 }
 
 /// Configuration for applying a [StatementContinuation] to an [Environment].
 class ForwardConfiguration extends Configuration {
   final StatementContinuation continuation;
   final Environment environment;
 
   ForwardConfiguration(this.continuation, this.environment);
 
   Configuration step(StatementExecuter _) => continuation?.call(environment);
@@ skipping 552 matching lines @@
 
   SetterEK(this.receiver, this.name, this.continuation);
 
   Configuration call(Value v) {
     Setter setter = receiver.class_.lookupImplicitSetter(name);
     setter(receiver, v);
     return new ValuePassingConfiguration(continuation, v);
   }
 }
 
+class StaticSetEK extends ExpressionContinuation {
+  final Member member;
+  final ExpressionContinuation continuation;
+
+  StaticSetEK(this.member, this.continuation);
+
+  Configuration call(Value v) {
+    Interpreter.mainEnvironment.update(member, v);
+    return new ValuePassingConfiguration(continuation, v);
+  }
+}
+
+class StaticSetterEK extends ExpressionContinuation {
+  final FunctionNode setter;
+  final ExceptionComponents exceptionComponents;
+  final ExpressionContinuation expressionContinuation;
+
+  StaticSetterEK(
+      this.setter, this.exceptionComponents, this.expressionContinuation);
+
+  Configuration call(Value v) {
+    VariableDeclaration arg = setter.positionalParameters.first;
+    var env = new Environment.empty().extend(arg, v);
+    var state = new State.initial()
+        .withException(exceptionComponents)
+        .withReturnContinuation(expressionContinuation)
+        .withContinuation(
+            new ExitSK(expressionContinuation, Value.nullInstance));
+
+    return new ExecConfiguration(setter.body, env, state);
+  }
+}
+
 /// Represents a continuation to be called after the evaluation of an actual
 /// argument for function invocation.
 class ExpressionListEK extends ExpressionContinuation {
   final InterpreterExpression currentExpression;
   final List<InterpreterExpression> expressions;
   final Environment environment;
   final ExceptionComponents exceptionComponents;
   final ApplicationContinuation applicationContinuation;
 
   ExpressionListEK(this.currentExpression, this.expressions, this.environment,
@@ skipping 518 matching lines @@
     return new EvalConfiguration(node.expression, conf.environment,
         conf.state.exceptionComponents, cont);
   }
 
   Configuration visitBlock(Block node, ExecConfiguration conf) {
     if (node.statements.isEmpty) {
       return new ForwardConfiguration(
           conf.state.continuation, conf.environment);
     }
 
-    var env = new Environment(conf.environment);
     var cont = new BlockSK.fromConfig(node.statements.skip(1).toList(), conf);
-    return new ExecConfiguration(
-        node.statements.first, env, conf.state.withContinuation(cont));
+    return new ExecConfiguration(node.statements.first, conf.environment,
+        conf.state.withContinuation(cont));
   }
 
   Configuration visitEmptyStatement(
       EmptyStatement node, ExecConfiguration conf) {
     return new ForwardConfiguration(conf.state.continuation, conf.environment);
   }
 
   Configuration visitIfStatement(IfStatement node, ExecConfiguration conf) {
     var cont = new IfConditionEK(
         node.then, node.otherwise, conf.environment, conf.state);
@@ skipping 396 matching lines @@
 /// Initializes all non initialized fields from the provided class to
 /// `Value.nullInstance` in the provided value.
 void _initializeNullFields(Class class_, Value value) {
   int startIndex = class_.superclass?.instanceSize ?? 0;
   for (int i = startIndex; i < class_.instanceSize; i++) {
     if (value.fields[i].value == null) {
       value.fields[i].value = Value.nullInstance;
     }
   }
 }