Introduce initial plumbing for type inference in fasta.

pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.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.
 
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
 ///
 /// Instances of these classes may be created using the factory methods in
 /// `ast_factory.dart`.
 ///
 /// Note that these classes represent the Dart language prior to desugaring.
 /// When a single Dart construct desugars to a tree containing multiple kernel
 /// AST nodes, the shadow class extends the kernel object at the top of the
 /// desugared tree.
 ///
 /// This means that in some cases multiple shadow classes may extend the same
 /// kernel class, because multiple constructs in Dart may desugar to a tree
 /// with the same kind of root node.
+import 'package:front_end/src/fasta/type_inference/type_inferrer.dart';

[ahe, 2017/04/18 15:49:59]

Relative?

 import 'package:kernel/ast.dart';
+import 'package:kernel/class_hierarchy.dart';
+import 'package:kernel/core_types.dart';
 
 /// Concrete shadow object representing a statement block in kernel form.
 class KernelBlock extends Block implements KernelStatement {
   KernelBlock(List<KernelStatement> statements) : super(statements);
+
+  @override
+  void _inferStatement(KernelTypeInferrer inferrer) {
+    // TODO(paulberry): implement.
+  }
 }
 
 /// Common base class for shadow objects representing expressions in kernel
 /// form.
-abstract class KernelExpression implements Expression {}
+abstract class KernelExpression implements Expression {
+  /// Calls back to [inferrer] to perform type inference for whatever concrete

[scheglov, 2017/04/18 20:09:48]

The reference [inferrer] is not resolved here.

[Paul Berry, 2017/04/18 22:49:13]

Good catch, thanks.  I meant the signature to be:

DartType _inferExpression(KernelTypeInferrer inferrer, DartType typeContext,
bool typeNeeded);

I'll fix in a follow-up CL.

+  /// type of [KernelExpression] this is.
+  DartType _inferExpression(DartType typeContext, bool typeNeeded);
+}
 
 /// Concrete shadow object representing a function expression in kernel form.
 class KernelFunctionExpression extends FunctionExpression
     implements KernelExpression {
   KernelFunctionExpression(FunctionNode function) : super(function);
+
+  @override
+  DartType _inferExpression(DartType typeContext, bool typeNeeded) {
+    // TODO(paulberry): implement.
+    return typeNeeded ? const DynamicType() : null;
+  }
 }
 
 /// Concrete shadow object representing an integer literal in kernel form.
 class KernelIntLiteral extends IntLiteral implements KernelExpression {
   KernelIntLiteral(int value) : super(value);
+
+  @override
+  DartType _inferExpression(DartType typeContext, bool typeNeeded) {
+    // TODO(paulberry): implement.
+    return typeNeeded ? const DynamicType() : null;
+  }
 }
 
 /// Concrete shadow object representing a list literal in kernel form.
 class KernelListLiteral extends ListLiteral implements KernelExpression {
   KernelListLiteral(List<KernelExpression> expressions,
       {DartType typeArgument, bool isConst: false})
       : super(expressions, typeArgument: typeArgument, isConst: isConst);
+
+  @override
+  DartType _inferExpression(DartType typeContext, bool typeNeeded) {
+    // TODO(paulberry): implement.
+    return typeNeeded ? const DynamicType() : null;
+  }
 }
 
 /// Concrete shadow object representing a null literal in kernel form.
-class KernelNullLiteral extends NullLiteral implements KernelExpression {}
+class KernelNullLiteral extends NullLiteral implements KernelExpression {
+  @override
+  DartType _inferExpression(DartType typeContext, bool typeNeeded) {
+    // TODO(paulberry): implement.
+    return typeNeeded ? const DynamicType() : null;
+  }
+}
 
 /// Concrete shadow object representing a return statement in kernel form.
 class KernelReturnStatement extends ReturnStatement implements KernelStatement {
   KernelReturnStatement([KernelExpression expression]) : super(expression);
+
+  @override
+  void _inferStatement(KernelTypeInferrer inferrer) {
+    // TODO(paulberry): implement.
+  }
 }
 
 /// Common base class for shadow objects representing statements in kernel
 /// form.
-abstract class KernelStatement extends Statement {}
+abstract class KernelStatement extends Statement {
+  /// Calls back to [inferrer] to perform type inference for whatever concrete
+  /// type of [KernelStatement] this is.
+  void _inferStatement(KernelTypeInferrer inferrer);
+}
+
+/// Concrete implementation of [TypeInferrer] specialized to work with kernel
+/// objects.
+class KernelTypeInferrer extends TypeInferrer<Statement, Expression,
+    KernelVariableDeclaration, Field> {
+  KernelTypeInferrer(CoreTypes coreTypes, ClassHierarchy classHierarchy)
+      : super(coreTypes, classHierarchy);
+
+  @override
+  DartType inferExpression(
+      Expression expression, DartType typeContext, bool typeNeeded) {
+    if (expression is KernelExpression) {
+      // Use polymorphic dispatch on [KernelExpression] to perform whatever kind
+      // of type inference is correct for this kind of statement.
+      // TODO(paulberry): experiment to see if dynamic dispatch would be better,
+      // so that the type hierarchy will be simpler (which may speed up "is"
+      // checks).
+      return expression._inferExpression(typeContext, typeNeeded);
+    } else {
+      // Encountered an expression type for which type inference is not yet
+      // implemented, so just infer dynamic for now.
+      // TODO(paulberry): once the BodyBuilder uses shadow classes for
+      // everything, this case should no longer be needed.
+      return typeNeeded ? const DynamicType() : null;
+    }
+  }
+
+  @override
+  void inferStatement(Statement statement) {
+    if (statement is KernelStatement) {
+      // Use polymorphic dispatch on [KernelStatement] to perform whatever kind
+      // of type inference is correct for this kind of statement.
+      // TODO(paulberry): experiment to see if dynamic dispatch would be better,
+      // so that the type hierarchy will be simpler (which may speed up "is"
+      // checks).
+      return statement._inferStatement(this);
+    } else {
+      // Encountered a statement type for which type inference is not yet
+      // implemented, so just skip it for now.
+      // TODO(paulberry): once the BodyBuilder uses shadow classes for
+      // everything, this case should no longer be needed.
+    }
+  }
+}
 
 /// Concrete shadow object representing a variable declaration in kernel form.
 class KernelVariableDeclaration extends VariableDeclaration
     implements KernelStatement {
   KernelVariableDeclaration(String name,
       {KernelExpression initializer,
       DartType type,
       bool isFinal: false,
       bool isConst: false})
       : super(name,
             initializer: initializer,
             type: type,
             isFinal: isFinal,
             isConst: isConst);
+
+  @override
+  void _inferStatement(KernelTypeInferrer inferrer) {
+    // TODO(paulberry): implement.
+  }
 }
 
 /// Concrete shadow object representing a read from a variable in kernel form.
 class KernelVariableGet extends VariableGet implements KernelExpression {
   KernelVariableGet(VariableDeclaration variable, [DartType promotedType])
       : super(variable, promotedType);
+
+  @override
+  DartType _inferExpression(DartType typeContext, bool typeNeeded) {
+    // TODO(paulberry): implement.
+    return typeNeeded ? const DynamicType() : null;
+  }
 }