Introduce initial plumbing for type promotion in fasta.

pkg/front_end/lib/src/fasta/kernel/fasta_accessors.dart

 // Copyright (c) 2016, 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 fasta.fasta_accessors;
 
 export 'frontend_accessors.dart' show wrapInvalid;
 
 import 'frontend_accessors.dart' show Accessor, buildIsNull, makeLet;
 
+import 'package:front_end/src/fasta/builder/ast_factory.dart' show AstFactory;
+
+import 'package:front_end/src/fasta/type_inference/type_promotion.dart'
+    show TypePromoter;
+
 import 'package:kernel/ast.dart';
 
 import '../errors.dart' show internalError;
 
 import '../scope.dart' show AccessErrorBuilder, ProblemBuilder, Scope;
 
 import 'frontend_accessors.dart' as kernel
     show
         IndexAccessor,
         NullAwarePropertyAccessor,
         PropertyAccessor,
         ReadOnlyAccessor,
         StaticAccessor,
         SuperIndexAccessor,
         SuperPropertyAccessor,
         ThisIndexAccessor,
         ThisPropertyAccessor,
         VariableAccessor;
 
 import 'kernel_builder.dart'
     show Builder, KernelClassBuilder, PrefixBuilder, TypeDeclarationBuilder;
 
 import '../names.dart' show callName;
 
 abstract class BuilderHelper {

[ahe, 2017/04/24 16:47:16]

BTW: If you have a suggestion for a better name for this interface, please let
me know.

[Paul Berry, 2017/04/24 18:20:30]

Ok, thanks.  So far I don't have any ideas.

   Uri get uri;
 
+  TypePromoter get typePromoter;
+
+  int get functionNestingLevel;
+
+  AstFactory get astFactory;
+
   Constructor lookupConstructor(Name name, {bool isSuper});
 
   Expression toSuperMethodInvocation(MethodInvocation node);
 
   Expression toValue(node);
 
   Member lookupSuperMember(Name name, {bool isSetter: false});
 
   scopeLookup(Scope scope, String name, int offset,
       {bool isQualified: false, PrefixBuilder prefix});
@@ skipping 754 matching lines @@
   String get plainNameForRead => name.name;
 
   Expression doInvocation(int offset, Arguments arguments) {
     return internalError("Not implemented yet.");
   }
 
   toString() => "NullAwarePropertyAccessor()";
 }
 
 class VariableAccessor extends kernel.VariableAccessor with FastaAccessor {
+  @override
   final BuilderHelper helper;
 
   VariableAccessor(this.helper, int offset, VariableDeclaration variable,
       [DartType promotedType])
       : super(variable, promotedType, offset);
 
   String get plainNameForRead => variable.name;
 
   Expression doInvocation(int offset, Arguments arguments) {
     // Normally the offset is at the start of the token, but in this case,
@@ skipping 70 matching lines @@
         new ConditionalExpression(
             buildIsNull(new VariableGet(variable)),
             new NullLiteral(),
             new MethodInvocation(new VariableGet(variable), name, arguments)
               ..fileOffset = offset,
             const DynamicType()));
   } else {
     return new MethodInvocation(receiver, name, arguments)..fileOffset = offset;
   }
 }