move TypeSystem classes to their own file

pkg/analyzer/lib/src/generated/resolver.dart

Index: pkg/analyzer/lib/src/generated/resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/resolver.dart b/pkg/analyzer/lib/src/generated/resolver.dart
index 91f49200bb8ba8c9299b6b07be71c78df2ecfde6..eece655cd05407e8e8272c2013139e7c23953036 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -6,8 +6,6 @@ library engine.resolver;
 
 import 'dart:collection';
 
-import 'package:analyzer/src/generated/scanner.dart';
-
 import 'ast.dart';
 import 'constant.dart';
 import 'element.dart';
@@ -18,12 +16,16 @@ import 'error_verifier.dart';
 import 'html.dart' as ht;
 import 'java_core.dart';
 import 'java_engine.dart';
+import 'scanner.dart';
 import 'scanner.dart' as sc;
 import 'sdk.dart' show DartSdk, SdkLibrary;
 import 'source.dart';
 import 'static_type_analyzer.dart';
+import 'type_system.dart';
 import 'utilities_dart.dart';
 
+export 'type_system.dart';
+
 /**
  * Callback signature used by ImplicitConstructorBuilder to register
  * computations to be performed, and their dependencies.  A call to this
@@ -46,10 +48,6 @@ typedef TypeResolverVisitor TypeResolverVisitorFactory(
 
 typedef void VoidFunction();
 
-typedef bool _GuardedSubtypeChecker<T>(T t1, T t2, Set<Element> visited);
-
-typedef bool _SubtypeChecker<T>(T t1, T t2);
-
 /**
  * Instances of the class `BestPracticesVerifier` traverse an AST structure looking for
  * violations of Dart best practices.
@@ -12806,307 +12804,6 @@ abstract class ScopedVisitor extends UnifyingAstVisitor<Object> {
 }
 
 /**
- * Implementation of [TypeSystem] using the strong mode rules.
- * https://github.com/dart-lang/dev_compiler/blob/master/STRONG_MODE.md
- */
-class StrongTypeSystemImpl implements TypeSystem {
-  final _specTypeSystem = new TypeSystemImpl();
-
-  StrongTypeSystemImpl();
-
-  @override
-  DartType getLeastUpperBound(
-      TypeProvider typeProvider, DartType type1, DartType type2) {
-    // TODO(leafp): Implement a strong mode version of this.
-    return _specTypeSystem.getLeastUpperBound(typeProvider, type1, type2);
-  }
-
-  // TODO(leafp): Document the rules in play here
-  @override
-  bool isAssignableTo(DartType fromType, DartType toType) {
-    // An actual subtype
-    if (isSubtypeOf(fromType, toType)) {
-      return true;
-    }
-
-    // Don't allow implicit downcasts between function types
-    // and call method objects, as these will almost always fail.
-    if ((fromType is FunctionType && _getCallMethodType(toType) != null) ||
-        (toType is FunctionType && _getCallMethodType(fromType) != null)) {
-      return false;
-    }
-
-    // If the subtype relation goes the other way, allow the implicit downcast.
-    // TODO(leafp): Emit warnings and hints for these in some way.
-    // TODO(leafp): Consider adding a flag to disable these?  Or just rely on
-    //   --warnings-as-errors?
-    if (isSubtypeOf(toType, fromType) ||
-        _specTypeSystem.isAssignableTo(toType, fromType)) {
-      // TODO(leafp): error if type is known to be exact (literal,
-      //  instance creation).
-      // TODO(leafp): Warn on composite downcast.
-      // TODO(leafp): hint on object/dynamic downcast.
-      // TODO(leafp): Consider allowing assignment casts.
-      return true;
-    }
-
-    return false;
-  }
-
-  @override
-  bool isSubtypeOf(DartType leftType, DartType rightType) {
-    return _isSubtypeOf(leftType, rightType, null);
-  }
-
-  FunctionType _getCallMethodType(DartType t) {
-    if (t is InterfaceType) {
-      return t.lookUpInheritedMethod("call")?.type;
-    }
-    return null;
-  }
-
-  // Given a type t, if t is an interface type with a call method
-  // defined, return the function type for the call method, otherwise
-  // return null.
-  _GuardedSubtypeChecker<DartType> _guard(
-      _GuardedSubtypeChecker<DartType> check) {
-    return (DartType t1, DartType t2, Set<Element> visited) {
-      Element element = t1.element;
-      if (visited == null) {
-        visited = new HashSet<Element>();
-      }
-      if (element == null || !visited.add(element)) {
-        return false;
-      }
-      try {
-        return check(t1, t2, visited);
-      } finally {
-        visited.remove(element);
-      }
-    };
-  }
-
-  bool _isBottom(DartType t, {bool dynamicIsBottom: false}) {
-    return (t.isDynamic && dynamicIsBottom) || t.isBottom;
-  }
-
-  // Guard against loops in the class hierarchy
-  /**
-   * Check that [f1] is a subtype of [f2].
-   * [fuzzyArrows] indicates whether or not the f1 and f2 should be
-   * treated as fuzzy arrow types (and hence dynamic parameters to f2 treated
-   * as bottom).
-   */
-  bool _isFunctionSubtypeOf(FunctionType f1, FunctionType f2,
-      {bool fuzzyArrows: true}) {
-    final r1s = f1.normalParameterTypes;
-    final o1s = f1.optionalParameterTypes;
-    final n1s = f1.namedParameterTypes;
-    final r2s = f2.normalParameterTypes;
-    final o2s = f2.optionalParameterTypes;
-    final n2s = f2.namedParameterTypes;
-    final ret1 = f1.returnType;
-    final ret2 = f2.returnType;
-
-    // A -> B <: C -> D if C <: A and
-    // either D is void or B <: D
-    if (!ret2.isVoid && !isSubtypeOf(ret1, ret2)) {
-      return false;
-    }
-
-    // Reject if one has named and the other has optional
-    if (n1s.length > 0 && o2s.length > 0) {
-      return false;
-    }
-    if (n2s.length > 0 && o1s.length > 0) {
-      return false;
-    }
-
-    // Rebind _isSubtypeOf for convenience
-    _SubtypeChecker<DartType> parameterSubtype = (DartType t1, DartType t2) =>
-        _isSubtypeOf(t1, t2, null, dynamicIsBottom: fuzzyArrows);
-
-    // f2 has named parameters
-    if (n2s.length > 0) {
-      // Check that every named parameter in f2 has a match in f1
-      for (String k2 in n2s.keys) {
-        if (!n1s.containsKey(k2)) {
-          return false;
-        }
-        if (!parameterSubtype(n2s[k2], n1s[k2])) {
-          return false;
-        }
-      }
-    }
-    // If we get here, we either have no named parameters,
-    // or else the named parameters match and we have no optional
-    // parameters
-
-    // If f1 has more required parameters, reject
-    if (r1s.length > r2s.length) {
-      return false;
-    }
-
-    // If f2 has more required + optional parameters, reject
-    if (r2s.length + o2s.length > r1s.length + o1s.length) {
-      return false;
-    }
-
-    // The parameter lists must look like the following at this point
-    // where rrr is a region of required, and ooo is a region of optionals.
-    // f1: rrr ooo ooo ooo
-    // f2: rrr rrr ooo
-    int rr = r1s.length; // required in both
-    int or = r2s.length - r1s.length; // optional in f1, required in f2
-    int oo = o2s.length; // optional in both
-
-    for (int i = 0; i < rr; ++i) {
-      if (!parameterSubtype(r2s[i], r1s[i])) {
-        return false;
-      }
-    }
-    for (int i = 0, j = rr; i < or; ++i, ++j) {
-      if (!parameterSubtype(r2s[j], o1s[i])) {
-        return false;
-      }
-    }
-    for (int i = or, j = 0; i < oo; ++i, ++j) {
-      if (!parameterSubtype(o2s[j], o1s[i])) {
-        return false;
-      }
-    }
-    return true;
-  }
-
-  bool _isInterfaceSubtypeOf(
-      InterfaceType i1, InterfaceType i2, Set<Element> visited) {
-    // Guard recursive calls
-    _GuardedSubtypeChecker<InterfaceType> guardedInterfaceSubtype =
-        _guard(_isInterfaceSubtypeOf);
-
-    if (i1 == i2) {
-      return true;
-    }
-
-    if (i1.element == i2.element) {
-      List<DartType> tArgs1 = i1.typeArguments;
-      List<DartType> tArgs2 = i2.typeArguments;
-
-      assert(tArgs1.length == tArgs2.length);
-
-      for (int i = 0; i < tArgs1.length; i++) {
-        DartType t1 = tArgs1[i];
-        DartType t2 = tArgs2[i];
-        if (!isSubtypeOf(t1, t2)) {
-          return false;
-        }
-      }
-      return true;
-    }
-
-    if (i2.isDartCoreFunction && i1.element.getMethod("call") != null) {
-      return true;
-    }
-
-    if (i1.isObject) {
-      return false;
-    }
-
-    if (guardedInterfaceSubtype(i1.superclass, i2, visited)) {
-      return true;
-    }
-
-    for (final parent in i1.interfaces) {
-      if (guardedInterfaceSubtype(parent, i2, visited)) {
-        return true;
-      }
-    }
-
-    for (final parent in i1.mixins) {
-      if (guardedInterfaceSubtype(parent, i2, visited)) {
-        return true;
-      }
-    }
-
-    return false;
-  }
-
-  bool _isSubtypeOf(DartType t1, DartType t2, Set<Element> visited,
-      {bool dynamicIsBottom: false}) {
-    // Guard recursive calls
-    _GuardedSubtypeChecker<DartType> guardedSubtype = _guard(_isSubtypeOf);
-
-    if (t1 == t2) {
-      return true;
-    }
-
-    // The types are void, dynamic, bottom, interface types, function types
-    // and type parameters.  We proceed by eliminating these different classes
-    // from consideration.
-
-    // Trivially true.
-    if (_isTop(t2, dynamicIsBottom: dynamicIsBottom) ||
-        _isBottom(t1, dynamicIsBottom: dynamicIsBottom)) {
-      return true;
-    }
-
-    // Trivially false.
-    if (_isTop(t1, dynamicIsBottom: dynamicIsBottom) ||
-        _isBottom(t2, dynamicIsBottom: dynamicIsBottom)) {
-      return false;
-    }
-
-    // S <: T where S is a type variable
-    //  T is not dynamic or object (handled above)
-    //  S != T (handled above)
-    //  So only true if bound of S is S' and
-    //  S' <: T
-    if (t1 is TypeParameterType) {
-      DartType bound = t1.element.bound;
-      if (bound == null) return false;
-      return guardedSubtype(bound, t2, visited);
-    }
-
-    if (t2 is TypeParameterType) {
-      return false;
-    }
-
-    if (t1.isVoid || t2.isVoid) {
-      return false;
-    }
-
-    // We've eliminated void, dynamic, bottom, and type parameters.  The only
-    // cases are the combinations of interface type and function type.
-
-    // A function type can only subtype an interface type if
-    // the interface type is Function
-    if (t1 is FunctionType && t2 is InterfaceType) {
-      return t2.isDartCoreFunction;
-    }
-
-    // An interface type can only subtype a function type if
-    // the interface type declares a call method with a type
-    // which is a super type of the function type.
-    if (t1 is InterfaceType && t2 is FunctionType) {
-      var callType = _getCallMethodType(t1);
-      return (callType != null) && _isFunctionSubtypeOf(callType, t2);
-    }
-
-    // Two interface types
-    if (t1 is InterfaceType && t2 is InterfaceType) {
-      return _isInterfaceSubtypeOf(t1, t2, visited);
-    }
-
-    return _isFunctionSubtypeOf(t1 as FunctionType, t2 as FunctionType);
-  }
-
-  // TODO(leafp): Document the rules in play here
-  bool _isTop(DartType t, {bool dynamicIsBottom: false}) {
-    return (t.isDynamic && !dynamicIsBottom) || t.isObject;
-  }
-}
-
-/**
  * Instances of this class manage the knowledge of what the set of subtypes are for a given type.
  */
 class SubtypeManager {
@@ -15332,139 +15029,6 @@ class TypeResolverVisitor extends ScopedVisitor {
 }
 
 /**
- * The interface `TypeSystem` defines the behavior of an object representing
- * the type system.  This provides a common location to put methods that act on
- * types but may need access to more global data structures, and it paves the
- * way for a possible future where we may wish to make the type system
- * pluggable.
- */
-abstract class TypeSystem {
-  /**
-   * Compute the least upper bound of two types.
-   */
-  DartType getLeastUpperBound(
-      TypeProvider typeProvider, DartType type1, DartType type2);
-
-  /**
-   * Return `true` if the [leftType] is assignable to the [rightType] (that is,
-   * if leftType <==> rightType).
-   */
-  bool isAssignableTo(DartType leftType, DartType rightType);
-
-  /**
-   * Return `true` if the [leftType] is a subtype of the [rightType] (that is,
-   * if leftType <: rightType).
-   */
-  bool isSubtypeOf(DartType leftType, DartType rightType);
-
-  /**
-   * Create either a strong mode or regular type system based on context.
-   */
-  static TypeSystem create(AnalysisContext context) {
-    return (context.analysisOptions.strongMode)
-        ? new StrongTypeSystemImpl()
-        : new TypeSystemImpl();
-  }
-}
-
-/**
- * Implementation of [TypeSystem] using the rules in the Dart specification.
- */
-class TypeSystemImpl implements TypeSystem {
-  TypeSystemImpl();
-
-  @override
-  DartType getLeastUpperBound(
-      TypeProvider typeProvider, DartType type1, DartType type2) {
-    // The least upper bound relation is reflexive.
-    if (identical(type1, type2)) {
-      return type1;
-    }
-    // The least upper bound of dynamic and any type T is dynamic.
-    if (type1.isDynamic) {
-      return type1;
-    }
-    if (type2.isDynamic) {
-      return type2;
-    }
-    // The least upper bound of void and any type T != dynamic is void.
-    if (type1.isVoid) {
-      return type1;
-    }
-    if (type2.isVoid) {
-      return type2;
-    }
-    // The least upper bound of bottom and any type T is T.
-    if (type1.isBottom) {
-      return type2;
-    }
-    if (type2.isBottom) {
-      return type1;
-    }
-    // Let U be a type variable with upper bound B.  The least upper bound of U
-    // and a type T is the least upper bound of B and T.
-    while (type1 is TypeParameterType) {
-      // TODO(paulberry): is this correct in the complex of F-bounded
-      // polymorphism?
-      DartType bound = (type1 as TypeParameterType).element.bound;
-      if (bound == null) {
-        bound = typeProvider.objectType;
-      }
-      type1 = bound;
-    }
-    while (type2 is TypeParameterType) {
-      // TODO(paulberry): is this correct in the context of F-bounded
-      // polymorphism?
-      DartType bound = (type2 as TypeParameterType).element.bound;
-      if (bound == null) {
-        bound = typeProvider.objectType;
-      }
-      type2 = bound;
-    }
-    // The least upper bound of a function type and an interface type T is the
-    // least upper bound of Function and T.
-    if (type1 is FunctionType && type2 is InterfaceType) {
-      type1 = typeProvider.functionType;
-    }
-    if (type2 is FunctionType && type1 is InterfaceType) {
-      type2 = typeProvider.functionType;
-    }
-
-    // At this point type1 and type2 should both either be interface types or
-    // function types.
-    if (type1 is InterfaceType && type2 is InterfaceType) {
-      InterfaceType result =
-          InterfaceTypeImpl.computeLeastUpperBound(type1, type2);
-      if (result == null) {
-        return typeProvider.dynamicType;
-      }
-      return result;
-    } else if (type1 is FunctionType && type2 is FunctionType) {
-      FunctionType result =
-          FunctionTypeImpl.computeLeastUpperBound(type1, type2);
-      if (result == null) {
-        return typeProvider.functionType;
-      }
-      return result;
-    } else {
-      // Should never happen.  As a defensive measure, return the dynamic type.
-      assert(false);
-      return typeProvider.dynamicType;
-    }
-  }
-
-  @override
-  bool isAssignableTo(DartType leftType, DartType rightType) {
-    return leftType.isAssignableTo(rightType);
-  }
-
-  @override
-  bool isSubtypeOf(DartType leftType, DartType rightType) {
-    return leftType.isSubtypeOf(rightType);
-  }
-}
-
-/**
  * Instances of the class [UnusedLocalElementsVerifier] traverse an element
  * structure looking for cases of [HintCode.UNUSED_ELEMENT],
  * [HintCode.UNUSED_FIELD], [HintCode.UNUSED_LOCAL_VARIABLE], etc.