Introduce initial plumbing for type inference in fasta.

pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart

Index: pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
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index 0000000000000000000000000000000000000000..e5f6a8bee5838edcffa88690ebd4413afc42cf6d
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+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
@@ -0,0 +1,51 @@
+// 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.md file.
+
+import 'package:kernel/ast.dart';

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

May want to use show on this import to be explicit about being independent of
the AST.

[Paul Berry, 2017/04/18 16:33:17]

Done.

+import 'package:kernel/class_hierarchy.dart';
+import 'package:kernel/core_types.dart';
+
+/// Abstract implementation of type inference which is independent of the
+/// underlying AST representation.

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

But still using DartType from kernel?

[Paul Berry, 2017/04/18 16:33:17]

Yes, for now at least.  I don't know if this will change or not.  I've added
documentation to this effect.

+///
+/// Derived classes should set S, E, V, and F to the class they use to represent
+/// statements, expressions, variable declarations, and field declarations,
+/// respectively.
+abstract class TypeInferrer<S, E, V, F> {
+  final CoreTypes coreTypes;
+
+  final ClassHierarchy classHierarchy;
+
+  /// The URI of the code for which type inference is currently being
+  /// performed--this is used for testing.
+  Uri uri;
+
+  TypeInferrer(this.coreTypes, this.classHierarchy);
+
+  /// Performs type inference on a method with the given method [body].
+  ///
+  /// [uri] is the URI of the file the method is contained in--this is used for
+  /// testing.
+  void inferBody(S body, Uri uri) {
+    this.uri = uri;
+    inferStatement(body);
+  }
+
+  /// Performs type inference on the given [expression].
+  ///
+  /// [typeContext] is the expected type of the expression, based on surrounding
+  /// code.  [typeNeeded] indicates whether it is necessary to compute the
+  /// actual type of the expression.  If [typeNeeded] is `true`, the actual type
+  /// of the expression is returned; otherwise `null` is returned.
+  ///
+  /// Derived classes should override this method with logic that dispatches on
+  /// the expression type and calls the appropriate specialized "infer" method.
+  DartType inferExpression(E expression, DartType typeContext, bool typeNeeded);
+
+  /// Performs type inference on the given [statement].
+  ///
+  /// Derived classes should override this method with logic that dispatches on
+  /// the statement type and calls the appropriate specialized "infer" method.
+  void inferStatement(S statement);
+}