Introduce a testing framework for use with fasta type inference.

pkg/front_end/lib/src/base/instrumentation.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.
+
+import 'package:kernel/ast.dart';
+
+/// Interface providing the ability to record property/value pairs associated
+/// with source file locations.  Intended to facilitate testing.
+abstract class Instrumentation {
+  /// Records a property/value pair associated with the given URI and offset.
+  void record(String property, Uri uri, int offset, InstrumentationValue value);
+}
+
+/// Interface for values recorded by [Instrumentation].
+abstract class InstrumentationValue {
+  const InstrumentationValue();
+
+  /// Converts the value to the string representation most suitable for
+  /// storing as an annotation in a source file.
+  ///
+  /// Invariant: `this.matches(this.canonicalize())` should always return
+  /// `true`.
+  String canonicalize();

[ahe, 2017/04/19 11:38:29]

Is this a potential gotcha? Perhaps we should just extend the specification of
toString?

[Paul Berry, 2017/04/19 13:20:09]

Good point.  Fixed.

+
+  /// Checks if the given String is an accurate description of this value.
+  ///
+  /// The default implementation just checks for equality with the return value
+  /// of [canonicalize], however derived classes may want a more sophisticated
+  /// implementation (e.g. to allow abbreviations in the description).
+  ///
+  /// Derived classes should ensure that the invariant holds:
+  /// `this.matches(this.canonicalize())` should always return `true`.
+  bool matches(String description) => description == canonicalize();
+}
+
+/// Instance of [InstrumentationValue] describing a [DartType].
+class InstrumentationValueForType extends InstrumentationValue {
+  final DartType type;
+
+  InstrumentationValueForType(this.type);
+
+  @override
+  String canonicalize() {
+    // Convert '→' to '->' because '→' doesn't show up in some terminals.
+    return type.toString().replaceAll('→', '->');
+  }
+}
+
+/// Instance of [InstrumentationValue] which only matches the given literal
+/// string.
+class InstrumentationValueLiteral extends InstrumentationValue {
+  final String value;
+
+  const InstrumentationValueLiteral(this.value);
+
+  @override
+  String canonicalize() => value;
+}