analyzer: Prepare some APIs for null safety; specify returns more accurately

Change-Id: Ia71bf5958d28c4229f68c0a1612cf44a2f283419
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/175903
Reviewed-by: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>

Author: srawlins

pkg/analyzer/lib/src/dart/constant/evaluation.dart

@@ -81,7 +81,7 @@ class ConstantEvaluationEngine {
   /// arguments are correct, `false` if there is an error.
   bool checkFromEnvironmentArguments(
       LibraryElementImpl library,
-      NodeList<Expression> arguments,
+      List<Expression> arguments,
       List<DartObjectImpl> argumentValues,
       Map<String, DartObjectImpl> namedArgumentValues,
       InterfaceType expectedDefaultValueType) {
@@ -271,7 +271,7 @@ class ConstantEvaluationEngine {
       constant = (constant as ConstructorElement).declaration;
     }
     if (constant is VariableElement) {
-      VariableElementImpl declaration = constant.declaration;
+      var declaration = constant.declaration as VariableElementImpl;
       Expression initializer = declaration.constantInitializer;
       if (initializer != null) {
         initializer.accept(referenceFinder);
@@ -497,7 +497,7 @@ class ConstantEvaluationEngine {
         definingType,
       );
     }
-    ConstructorElementImpl constructorBase = constructor.declaration;
+    var constructorBase = constructor.declaration as ConstructorElementImpl;
     List<ConstructorInitializer> initializers =
         constructorBase.constantInitializers;
     if (initializers == null) {
@@ -1550,7 +1550,7 @@ class ConstantVisitor extends UnifyingAstVisitor<DartObjectImpl> {
       return false;
     } else if (element is SpreadElement) {
       DartObjectImpl elementResult = element.expression.accept(this);
-      Map<DartObject, DartObject> value = elementResult?.toMapValue();
+      Map<DartObjectImpl, DartObjectImpl> value = elementResult?.toMapValue();
       if (value == null) {
         return true;
       }
@@ -1662,9 +1662,9 @@ class ConstantVisitor extends UnifyingAstVisitor<DartObjectImpl> {
         return value.value;
       }
     } else if (variableElement is ExecutableElement) {
-      ExecutableElement function = element;
+      var function = element as ExecutableElement;
       if (function.isStatic) {
-        var functionType = node.staticType;
+        var functionType = node.staticType as ParameterizedType;
         return DartObjectImpl(
           typeSystem,
           functionType,

pkg/analyzer/lib/src/dart/element/element.dart

@@ -267,7 +267,8 @@ abstract class AbstractClassElementImpl extends ElementImpl
   /// This method should be used only for error recovery during analysis,
   /// when instance access to a static class member, defined in this class,
   /// or a superclass.
-  ExecutableElement lookupStaticGetter(String name, LibraryElement library) {
+  PropertyAccessorElement lookupStaticGetter(
+      String name, LibraryElement library) {
     return _first(_implementationsOfGetter(name).where((element) {
       return element.isStatic && element.isAccessibleIn(library);
     }));
@@ -278,7 +279,7 @@ abstract class AbstractClassElementImpl extends ElementImpl
   /// This method should be used only for error recovery during analysis,
   /// when instance access to a static class member, defined in this class,
   /// or a superclass.
-  ExecutableElement lookupStaticMethod(String name, LibraryElement library) {
+  MethodElement lookupStaticMethod(String name, LibraryElement library) {
     return _first(_implementationsOfMethod(name).where((element) {
       return element.isStatic && element.isAccessibleIn(library);
     }));
@@ -289,7 +290,8 @@ abstract class AbstractClassElementImpl extends ElementImpl
   /// This method should be used only for error recovery during analysis,
   /// when instance access to a static class member, defined in this class,
   /// or a superclass.
-  ExecutableElement lookupStaticSetter(String name, LibraryElement library) {
+  PropertyAccessorElement lookupStaticSetter(
+      String name, LibraryElement library) {
     return _first(_implementationsOfSetter(name).where((element) {
       return element.isStatic && element.isAccessibleIn(library);
     }));
@@ -631,7 +633,7 @@ class ClassElementImpl extends AbstractClassElementImpl
   bool get hasNoSuchMethod {
     MethodElement method = lookUpConcreteMethod(
         FunctionElement.NO_SUCH_METHOD_METHOD_NAME, library);
-    ClassElement definingClass = method?.enclosingElement;
+    var definingClass = method?.enclosingElement as ClassElement;
     return definingClass != null && !definingClass.isDartCoreObject;
   }
 
@@ -902,7 +904,7 @@ class ClassElementImpl extends AbstractClassElementImpl
       return <ConstructorElement>[];
     }
 
-    ClassElementImpl superElement = supertype.element;
+    var superElement = supertype.element as ClassElementImpl;
 
     // First get the list of constructors of the superclass which need to be
     // forwarded to this class.
@@ -7275,7 +7277,7 @@ class TypeParameterElementImpl extends ElementImpl
   @override
   String get name {
     if (linkedNode != null) {
-      TypeParameter node = linkedNode;
+      var node = linkedNode as TypeParameter;
       return node.name.name;
     }
     return super.name;

pkg/analyzer/lib/src/dart/element/inheritance_manager3.dart

@@ -743,7 +743,7 @@ class InheritanceManager3 {
     FunctionType resultType;
     for (var executable in validOverrides) {
       var type = executable.type;
-      var normalizedType = typeSystem.normalize(type);
+      var normalizedType = typeSystem.normalize(type) as FunctionType;
       if (resultType == null) {
         resultType = normalizedType;
       } else {

pkg/analyzer/lib/src/dart/element/member.dart

@@ -7,7 +7,6 @@ import 'package:analyzer/dart/constant/value.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/nullability_suffix.dart';
 import 'package:analyzer/dart/element/type.dart';
-import 'package:analyzer/dart/element/type_provider.dart';
 import 'package:analyzer/src/dart/element/display_string_builder.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/nullability_eliminator.dart';
@@ -220,7 +219,7 @@ abstract class ExecutableMember extends Member implements ExecutableElement {
       return null;
     }
 
-    TypeProvider typeProvider;
+    TypeProviderImpl typeProvider;
     var isLegacy = false;
     var combined = substitution;
     if (element is ExecutableMember) {
@@ -237,7 +236,7 @@ abstract class ExecutableMember extends Member implements ExecutableElement {
       map.addAll(substitution.map);
       combined = Substitution.fromMap(map);
     } else {
-      typeProvider = element.library.typeProvider;
+      typeProvider = element.library.typeProvider as TypeProviderImpl;
     }
 
     if (!isLegacy && combined.map.isEmpty) {

pkg/analyzer/lib/src/dart/element/type.dart

@@ -1468,12 +1468,12 @@ class InterfaceTypeImpl extends TypeImpl implements InterfaceType {
   /// search should include the target type. The [visitedInterfaces] is a set
   /// containing all of the interfaces that have been examined, used to prevent
   /// infinite recursion and to optimize the search.
-  static ExecutableElement _lookUpMemberInInterfaces(
+  static T _lookUpMemberInInterfaces<T extends ExecutableElement>(
       InterfaceType targetType,
       bool includeTargetType,
       LibraryElement library,
       HashSet<ClassElement> visitedInterfaces,
-      ExecutableElement Function(InterfaceType type) getMember) {
+      T Function(InterfaceType type) getMember) {
     // TODO(brianwilkerson) This isn't correct. Section 8.1.1 of the
     // specification (titled "Inheritance and Overriding" under "Interfaces")
     // describes a much more complex scheme for finding the inherited member.

pkg/analyzer/lib/src/dart/element/type_algebra.dart

@@ -160,7 +160,7 @@ abstract class Substitution {
 
   /// Substitutes the type parameters on the class of [type] with the
   /// type arguments provided in [type].
-  static Substitution fromInterfaceType(InterfaceType type) {
+  static MapSubstitution fromInterfaceType(InterfaceType type) {
     if (type.typeArguments.isEmpty) {
       return _NullSubstitution.instance;
     }

pkg/analyzer/lib/src/error/correct_override.dart

@@ -189,7 +189,7 @@ class CovariantParametersVerifier {
   /// Return the [Substitution] to convert types of [superMember] to types of
   /// [_thisMember].
   Substitution _superSubstitution(_SuperMember superMember) {
-    var result = Substitution.fromInterfaceType(superMember.interface);
+    Substitution result = Substitution.fromInterfaceType(superMember.interface);
 
     // If the executable has type parameters, ensure that super uses the same.
     var thisTypeParameters = _thisMember.typeParameters;