[dart2js] Prep js_emitter/program_builder.dart for migration to null safety.

Change-Id: I95b3255706d2d6b4015555361416e3636e0965da
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/268406
Reviewed-by: Mayank Patke <fishythefish@google.com>
Commit-Queue: Nate Biggs <natebiggs@google.com>

Author: natebiggs

pkg/compiler/lib/src/js_backend/impact_transformer.dart

@@ -9,7 +9,7 @@ import '../common/codegen_interfaces.dart' show CodegenImpact;
 import '../constants/values.dart';
 import '../elements/entities.dart';
 import '../elements/types.dart';
-import '../js_emitter/interfaces.dart' show NativeEmitter;
+import '../js_emitter/native_emitter.dart';
 import '../js_model/js_world.dart';
 import '../native/enqueue.dart';
 import '../native/behavior.dart';

pkg/compiler/lib/src/js_emitter/class_stub_generator.dart

@@ -212,7 +212,7 @@ class ClassStubGenerator {
     jsAst.Expression code;
     if (field.isElided) {
       code = js("function() { return #; }",
-          _emitter.constantReference(field.constantValue));
+          _emitter.constantReference(field.constantValue!));
     } else {
       String template;
       if (field.needsInterceptedGetterOnReceiver) {

pkg/compiler/lib/src/js_emitter/code_emitter_task.dart

@@ -247,6 +247,7 @@ abstract class Emitter implements ModularEmitter, interfaces.Emitter {
 
   @override
   int compareConstants(ConstantValue a, ConstantValue b);
+  @override
   bool isConstantInlinedOrAlreadyEmitted(ConstantValue constant);
 
   /// Returns the size of the code generated for a given output [unit].

pkg/compiler/lib/src/js_emitter/interfaces.dart

@@ -12,6 +12,7 @@ import '../elements/entities.dart';
 import '../js/js.dart' as jsAst;
 
 import 'metadata_collector.dart' show MetadataCollector;
+import 'native_emitter.dart';
 import 'startup_emitter/fragment_merger.dart';
 
 abstract class CodeEmitterTask {
@@ -22,19 +23,6 @@ abstract class CodeEmitterTask {
   MetadataCollector get metadataCollector;
 }
 
-abstract class NativeEmitter {
-  Map<ClassEntity, List<ClassEntity>> get subtypes;
-  Map<ClassEntity, List<ClassEntity>> get directSubtypes;
-  Set<FunctionEntity> get nativeMethods;
-  List<jsAst.Statement> generateParameterStubStatements(
-      FunctionEntity member,
-      bool isInterceptedMethod,
-      jsAst.Name invocationName,
-      List<jsAst.Parameter> stubParameters,
-      List<jsAst.Expression> argumentsBuffer,
-      int indexOfLastOptionalArgumentInParameters);
-}
-
 abstract class ModularEmitter {
   jsAst.Expression constructorAccess(ClassEntity e);
   jsAst.Expression constantReference(ConstantValue constant);
@@ -55,4 +43,5 @@ abstract class Emitter extends ModularEmitter {
   jsAst.Expression generateEmbeddedGlobalAccess(String global);
   int compareConstants(ConstantValue a, ConstantValue b);
   jsAst.Expression interceptorClassAccess(ClassEntity e);
+  bool isConstantInlinedOrAlreadyEmitted(ConstantValue constant);
 }

pkg/compiler/lib/src/js_emitter/metadata_collector.dart

@@ -139,7 +139,7 @@ class MetadataCollector implements jsAst.TokenFinalizer {
     }
   }
 
-  jsAst.Expression? reifyType(DartType type, OutputUnit outputUnit) {
+  jsAst.Expression reifyType(DartType type, OutputUnit outputUnit) {
     return _addTypeInOutputUnit(type, outputUnit);
   }
 

pkg/compiler/lib/src/js_emitter/model.dart

@@ -21,7 +21,7 @@ class Program {
 
   // If this field is not `null` then its value must be emitted in the embedded
   // global `TYPE_TO_INTERCEPTOR_MAP`. The map references constants and classes.
-  final js.Expression typeToInterceptorMap;
+  final js.Expression? typeToInterceptorMap;
 
   // TODO(floitsch): we should store the metadata directly instead of storing
   // the collector. However, the old emitter still updates the data.
@@ -173,7 +173,8 @@ class StaticField {
   final FieldEntity element;
 
   final js.Name name;
-  final js.Name getterName;
+  // Null for static non-final fields.
+  final js.Name? getterName;
   // TODO(floitsch): the holder for static fields is the isolate object. We
   // could remove this field and use the isolate object directly.
   final js.Expression code;
@@ -252,7 +253,7 @@ class Class {
 
   // If the class implements a function type, and the type is encoded in the
   // metatada table, then this field contains the index into that field.
-  final js.Expression functionTypeIndex;
+  final js.Expression? functionTypeIndex;
 
   /// Whether the class must be evaluated eagerly.
   bool isEager = false;
@@ -305,11 +306,11 @@ class MixinApplication extends Class {
       List<StubMethod> checkedSetters,
       List<StubMethod> gettersSetters,
       List<StubMethod> isChecks,
-      js.Expression functionTypeIndex,
-      {required bool hasRtiField,
-      required bool onlyForRti,
-      required bool onlyForConstructor,
-      required bool isDirectlyInstantiated})
+      js.Expression? functionTypeIndex,
+      {required super.hasRtiField,
+      required super.onlyForRti,
+      required super.onlyForConstructor,
+      required super.isDirectlyInstantiated})
       : super(
             element,
             typeData,
@@ -322,10 +323,6 @@ class MixinApplication extends Class {
             gettersSetters,
             isChecks,
             functionTypeIndex,
-            hasRtiField: hasRtiField,
-            onlyForRti: onlyForRti,
-            onlyForConstructor: onlyForConstructor,
-            isDirectlyInstantiated: isDirectlyInstantiated,
             isNative: false,
             isClosureBaseClass: false,
             isMixinApplicationWithMembers: false);
@@ -363,9 +360,9 @@ class Field {
 
   final bool needsCheckedSetter;
 
-  final ConstantValue initializerInAllocator;
+  final ConstantValue? initializerInAllocator;
 
-  final ConstantValue constantValue;
+  final ConstantValue? constantValue;
 
   final bool isElided;
 
@@ -488,7 +485,7 @@ class InstanceMethod extends DartMethod {
     super.name,
     super.code,
     super.parameterStubs,
-    js.Name super.callName, {
+    super.callName, {
     required super.needsTearOff,
     super.tearOffName,
     this.aliasName,
@@ -559,7 +556,7 @@ abstract class StaticMethod implements Method {}
 
 class StaticDartMethod extends DartMethod implements StaticMethod {
   StaticDartMethod(super.element, super.name, super.code, super.parameterStubs,
-      js.Name super.callName,
+      super.callName,
       {required super.needsTearOff,
       super.tearOffName,
       required super.canBeApplied,

pkg/compiler/lib/src/js_emitter/native_emitter.dart

@@ -17,9 +17,8 @@ import '../native/enqueue.dart' show NativeCodegenEnqueuer;
 
 import 'interfaces.dart' show CodeEmitterTask;
 import 'model.dart';
-import 'interfaces.dart' as interfaces;
 
-class NativeEmitter implements interfaces.NativeEmitter {
+class NativeEmitter {
   final CodeEmitterTask _emitterTask;
   final JClosedWorld _closedWorld;
   final NativeCodegenEnqueuer _nativeCodegenEnqueuer;
@@ -28,15 +27,12 @@ class NativeEmitter implements interfaces.NativeEmitter {
   bool hasNativeClasses = false;
 
   // Caches the native subtypes of a native class.
-  @override
   Map<ClassEntity, List<ClassEntity>> subtypes = {};
 
-  @override
   // Caches the direct native subtypes of a native class.
   Map<ClassEntity, List<ClassEntity>> directSubtypes = {};
 
   // Caches the methods that have a native body.
-  @override
   Set<FunctionEntity> nativeMethods = {};
 
   // Type metadata redirections, where the key is the class type data being
@@ -314,7 +310,6 @@ class NativeEmitter implements interfaces.NativeEmitter {
     });
   }
 
-  @override
   List<jsAst.Statement> generateParameterStubStatements(
       FunctionEntity member,
       bool isInterceptedMethod,

pkg/compiler/lib/src/js_emitter/program_builder/program_builder.dart

@@ -41,17 +41,14 @@ import '../../universe/class_hierarchy.dart';
 import '../../universe/codegen_world_builder.dart';
 import '../../universe/selector.dart' show Selector;
 import '../../universe/world_builder.dart' show SelectorConstraints;
-import '../js_emitter.dart'
-    show
-        ClassStubGenerator,
-        CodeEmitterTask,
-        Emitter,
-        InstantiationStubGenerator,
-        InterceptorStubGenerator,
-        MainCallStubGenerator,
-        ParameterStubGenerator,
-        RuntimeTypeGenerator,
-        TypeTestProperties;
+import '../class_stub_generator.dart' show ClassStubGenerator;
+import '../instantiation_stub_generator.dart' show InstantiationStubGenerator;
+import '../interceptor_stub_generator.dart' show InterceptorStubGenerator;
+import '../main_call_stub_generator.dart' show MainCallStubGenerator;
+import '../parameter_stub_generator.dart' show ParameterStubGenerator;
+import '../runtime_type_generator.dart'
+    show RuntimeTypeGenerator, TypeTestProperties;
+import '../interfaces.dart' show CodeEmitterTask, Emitter;
 import '../model.dart';
 import '../sorter.dart';
 

pkg/compiler/lib/src/native/enqueue.dart

@@ -6,7 +6,8 @@ import '../common/elements.dart' show CommonElements, ElementEnvironment;
 import '../elements/entities.dart';
 import '../elements/types.dart';
 import '../js_backend/native_data.dart' show NativeData;
-import '../js_emitter/interfaces.dart' show CodeEmitterTask, NativeEmitter;
+import '../js_emitter/interfaces.dart' show CodeEmitterTask;
+import '../js_emitter/native_emitter.dart';
 import '../options.dart';
 import '../universe/use.dart' show TypeUse;
 import '../universe/world_impact.dart'