Split up TypeInferrer class.

pkg/front_end/lib/src/fasta/type_inference/type_inference_engine.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.md file.
+
+import 'package:front_end/src/base/instrumentation.dart';
+import 'package:front_end/src/dependency_walker.dart' as dependencyWalker;
+import 'package:front_end/src/fasta/type_inference/type_inferrer.dart';
+import 'package:kernel/ast.dart' show DartType, DynamicType;
+import 'package:kernel/class_hierarchy.dart';
+import 'package:kernel/core_types.dart';
+
+/// Data structure for tracking dependencies between fields that require type
+/// inference.
+///
+/// TODO(paulberry): see if it's possible to make this class more lightweight
+/// by changing the API so that the walker is passed to computeDependencies().
+/// (This should allow us to drop the _typeInferenceEngine field).
+class FieldNode<F> extends dependencyWalker.Node<FieldNode<F>> {
+  final TypeInferenceEngineImpl _typeInferenceEngine;
+
+  final F _field;
+
+  final dependencies = <FieldNode<F>>[];
+
+  FieldNode(this._typeInferenceEngine, this._field);
+
+  @override
+  bool get isEvaluated => _typeInferenceEngine.isFieldInferred(_field);
+
+  @override
+  List<FieldNode<F>> computeDependencies() {
+    return dependencies;
+  }
+}
+
+/// Keeps track of the global state for the type inference that occurs outside
+/// of method bodies and initalizers.
+///
+/// This class abstracts away the representation of the underlying AST using
+/// generic parameters.  TODO(paulberry): would it make more sense to abstract
+/// away the representation of types as well?
+///
+/// Derived classes should set F to the class they use to represent field
+/// declarations.
+///
+/// This class describes the interface for use by clients of type inference
+/// (e.g. DietListener).  Derived classes should derive from
+/// [TypeInferenceEngineImpl].
+abstract class TypeInferenceEngine<F> {
+  ClassHierarchy get classHierarchy;
+
+  CoreTypes get coreTypes;
+
+  /// Creates a type inferrer for use inside of a method body declared in a file
+  /// with the given [uri].
+  TypeInferrer<dynamic, dynamic, dynamic, F> createLocalTypeInferrer(Uri uri);
+
+  /// Creates a [TypeInferrer] object which is ready to perform type inference
+  /// on the given [field].
+  TypeInferrer<dynamic, dynamic, dynamic, F> createTopLevelTypeInferrer(
+      F field);
+
+  /// Performs the second phase of top level initializer inference, which is to
+  /// visit all fields and top level variables that were passed to [recordField]
+  /// in topologically-sorted order and assign their types.
+  void finishTopLevel();
+
+  /// Gets the list of top level type inference dependencies of the given
+  /// [field].
+  List<FieldNode<F>> getFieldDependencies(F field);
+
+  /// Gets ready to do top level type inference for the program having the given
+  /// [hierarchy], using the given [coreTypes].
+  void prepareTopLevel(CoreTypes coreTypes, ClassHierarchy hierarchy);
+
+  /// Records that the given [field] will need top level type inference.
+  void recordField(F field);
+}
+
+/// Derived class containing generic implementations of
+/// [TypeInferenceEngineImpl].
+///
+/// This class contains as much of the implementation of type inference as
+/// possible without knowing the identity of the type parameter.  It defers to
+/// abstract methods for everything else.
+abstract class TypeInferenceEngineImpl<F> extends TypeInferenceEngine<F> {
+  final Instrumentation instrumentation;
+
+  final bool strongMode;
+
+  final fieldNodes = <FieldNode<F>>[];
+
+  @override
+  CoreTypes coreTypes;
+
+  @override
+  ClassHierarchy classHierarchy;
+
+  TypeInferenceEngineImpl(this.instrumentation, this.strongMode);
+
+  /// Cleares the initializer of [field].
+  void clearFieldInitializer(F field);
+
+  /// Creates a [FieldNode] to track dependencies of the given [field].
+  FieldNode<F> createFieldNode(F field);
+
+  /// Queries whether the given [field] has an initializer.
+  bool fieldHasInitializer(F field);
+
+  @override
+  void finishTopLevel() {
+    for (var fieldNode in fieldNodes) {
+      if (fieldNode.isEvaluated) continue;
+      new _FieldWalker<F>().walk(fieldNode);
+    }
+  }
+
+  /// Gets the declared type of the given [field], or `null` if the type is
+  /// implicit.
+  DartType getFieldDeclaredType(F field);
+
+  /// Gets the character offset of the declaration of [field] within its
+  /// compilation unit.
+  int getFieldOffset(F field);
+
+  /// Retrieve the [TypeInferrer] for the given [field], which was created by
+  /// a previous call to [createTopLevelTypeInferrer].
+  TypeInferrerImpl<dynamic, dynamic, dynamic, F> getFieldTypeInferrer(F field);
+
+  /// Gets the URI of the compilation unit the [field] is declared in.
+  /// TODO(paulberry): can we remove this?
+  String getFieldUri(F field);
+
+  /// Performs type inference on the given [field].
+  void inferField(F field) {
+    if (fieldHasInitializer(field)) {
+      var typeInferrer = getFieldTypeInferrer(field);
+      var type = getFieldDeclaredType(field);
+      var inferredType =
+          typeInferrer.inferFieldInitializer(field, type, type == null);
+      if (type == null && strongMode) {
+        instrumentation?.record(
+            'topType',
+            Uri.parse(typeInferrer.uri),
+            getFieldOffset(field),
+            new InstrumentationValueForType(inferredType));
+        setFieldInferredType(field, inferredType);
+      }
+      // TODO(paulberry): if type != null, then check that the type of the
+      // initializer is assignable to it.
+      // TODO(paulberry): the following is a hack so that outlines don't contain
+      // initializers.  But it means that we rebuild the initializers when doing
+      // a full compile.  There should be a better way.
+      clearFieldInitializer(field);
+    }
+  }
+
+  /// Makes a note that the given [field] is part of a circularity, so its type
+  /// can't be inferred.
+  void inferFieldCircular(F field) {
+    // TODO(paulberry): report the appropriate error.
+    if (getFieldDeclaredType(field) == null) {
+      var uri = getFieldTypeInferrer(field).uri;
+      instrumentation?.record('topType', Uri.parse(uri), getFieldOffset(field),
+          const InstrumentationValueLiteral('circular'));
+      setFieldInferredType(field, const DynamicType());
+    }
+  }
+
+  /// Determines if top level type inference has been completed for [field].
+  bool isFieldInferred(F field);
+
+  @override
+  void prepareTopLevel(CoreTypes coreTypes, ClassHierarchy hierarchy) {
+    this.coreTypes = coreTypes;
+    this.classHierarchy = classHierarchy;
+  }
+
+  @override
+  void recordField(F field) {
+    fieldNodes.add(createFieldNode(field));
+  }
+
+  /// Stores [inferredType] as the inferred type of [field].
+  void setFieldInferredType(F field, DartType inferredType);
+}
+
+/// Subtype of [dependencyWalker.DependencyWalker] which is specialized to
+/// perform top level type inference.
+class _FieldWalker<F> extends dependencyWalker.DependencyWalker<FieldNode<F>> {
+  _FieldWalker();
+
+  @override
+  void evaluate(FieldNode<F> f) {
+    f._typeInferenceEngine.inferField(f._field);
+  }
+
+  @override
+  void evaluateScc(List<FieldNode<F>> scc) {
+    for (var f in scc) {
+      f._typeInferenceEngine.inferFieldCircular(f._field);
+    }
+    for (var f in scc) {
+      f._typeInferenceEngine.inferField(f._field);
+    }
+  }
+}