Transitive inference using SCC

lib/src/options.dart

 // Copyright (c) 2014, 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.
 
 /// Set of flags and options passed to the compiler
 library dev_compiler.src.options;
 
 import 'dart:io';
 
 import 'package:args/args.dart';
@@ skipping 16 matching lines @@
 
   /// Whether to infer return types and field types from overriden members.
   final bool inferFromOverrides;
   static const inferFromOverridesDefault = true;
 
   /// Whether to infer types for consts and fields by looking at initializers on
   /// the RHS. For example, in a constant declaration like:
   ///
   ///      const A = B;
   ///
-  /// We can infer the type of `A` based on the type of `B`. The current
-  /// implementation of this inference is limited to ensure the answer is
-  /// deterministic when applying inference on library cycles. In the example
-  /// above, `A` is inferred to have `B`'s declared type if they are both in the
-  /// same library cycle. However, if `B`'s definition is not in the same
-  /// connected component as `A`, we use `B`'s inferred type instead.
+  /// We can infer the type of `A` based on the type of `B`. The inference
+  /// algorithm determines what variables depend on others, and computes types
+  /// by visiting the variable dependency graph in topological order. This
+  /// ensures that the inferred type is deterministic when applying inference on
+  /// library cycles.
   ///
-  /// Because this might be surprising to users, this is turned off by default.
-  /// In the future, inference might track dependencies between variables in
-  /// more detail so that, in the example above, we can use `B`'s inferred type
-  /// always.
+  /// When this feature is turned off, we don't use the type of `B` to infer the
+  /// type of `A`, even if `B` has a declared type.
   final bool inferTransitively;
-  static const inferTransitivelyDefault = false;
+  static const inferTransitivelyDefault = true;
 
   /// Restrict inference of fields and top-levels to those that are final and
   /// const.
   final bool onlyInferConstsAndFinalFields;
   static const onlyInferConstAndFinalFieldsDefault = false;
 
   ResolverOptions({this.useMultiPackage: false, this.packageRoot: 'packages/',
       this.packagePaths: const <String>[],
       this.inferFromOverrides: inferFromOverridesDefault,
       this.inferTransitively: inferTransitivelyDefault,
@@ skipping 335 matching lines @@
     // The pub-cache directory is two levels up, but we verify that the layout
     // looks correct.
     if (path.basename(dir) != 'dev_compiler') return null;
     dir = path.dirname(dir);
     if (path.basename(dir) != 'global_packages') return null;
     dir = path.dirname(dir);
     return path.join(dir, cacheDir, 'lib', 'runtime');
   }
   return null;
 }