[dart2js] Treat Object as a top type in weak mode.

We were only treating Object as a top type if NNBD was disabled. This is
incorrect and we should be treating Object as a top type whenever legacy
subtyping is in effect. In particular, Object acts as a top type in weak
mode.

Change-Id: I76acc25e92fda2b9e2b7872fc72d319161318874
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/144689
Reviewed-by: Stephen Adams <sra@google.com>
Commit-Queue: Mayank Patke <fishythefish@google.com>

pkg/compiler/lib/src/diagnostics/messages.dart

@@ -663,7 +663,6 @@ class Message {
   final CompilerOptions _options;
   bool get terse => _options?.terseDiagnostics ?? false;
   bool get _printLegacyStars => _options?.printLegacyStars ?? false;
-  bool get _useNullSafety => _options?.useNullSafety ?? true;
   bool get _useLegacySubtyping => _options?.useLegacySubtyping ?? false;
   String message;
 
@@ -716,7 +715,6 @@ class Message {
     if (value is DartType) {
       value = value.toStructuredText(
           printLegacyStars: _printLegacyStars,
-          useNullSafety: _useNullSafety,
           useLegacySubtyping: _useLegacySubtyping);
     } else if (value is ConstantValue) {
       value = value.toDartText();

pkg/compiler/lib/src/elements/types.dart

@@ -92,15 +92,15 @@ abstract class DartType {
   DartType get withoutNullability => this;
 
   /// Is `true` if this type is a top type but not a legacy top type.
-  bool _isStrongTop(bool useNullSafety) => false;
+  bool _isStrongTop(bool useLegacySubtyping) => false;
 
   /// Is `true` if this type is a top type.
-  bool _isTop(bool useNullSafety) => _isStrongTop(useNullSafety);
+  bool _isTop(bool useLegacySubtyping) => _isStrongTop(useLegacySubtyping);
 
   /// Is `true` if every type argument of this type is a top type.
   // TODO(fishythefish): Should we instead check if each type argument is at its
   // bound?
-  bool _treatAsRaw(bool useNullSafety) => true;
+  bool _treatAsRaw(bool useLegacySubtyping) => true;
 
   /// Whether this type contains a type variable.
   bool get containsTypeVariables => false;
@@ -131,12 +131,8 @@ abstract class DartType {
   String toString() => toStructuredText();
 
   String toStructuredText(
-          {bool printLegacyStars = true,
-          bool useNullSafety = true,
-          bool useLegacySubtyping = false}) =>
-      _DartTypeToStringVisitor(
-              printLegacyStars, useNullSafety, useLegacySubtyping)
-          .run(this);
+          {bool printLegacyStars = true, bool useLegacySubtyping = false}) =>
+      _DartTypeToStringVisitor(printLegacyStars, useLegacySubtyping).run(this);
 }
 
 /// Pairs of [FunctionTypeVariable]s that are currently assumed to be
@@ -237,10 +233,11 @@ class LegacyType extends DartType {
   DartType get withoutNullability => baseType;
 
   @override
-  bool _isTop(bool useNullSafety) => baseType.isObject;
+  bool _isTop(bool useLegacySubtyping) => baseType.isObject;
 
   @override
-  bool _treatAsRaw(bool useNullSafety) => baseType._treatAsRaw(useNullSafety);
+  bool _treatAsRaw(bool useLegacySubtyping) =>
+      baseType._treatAsRaw(useLegacySubtyping);
 
   @override
   bool get containsTypeVariables => baseType.containsTypeVariables;
@@ -298,10 +295,11 @@ class NullableType extends DartType {
   DartType get withoutNullability => baseType;
 
   @override
-  bool _isStrongTop(bool isLegacy) => baseType.isObject;
+  bool _isStrongTop(bool useLegacySubtyping) => baseType.isObject;
 
   @override
-  bool _treatAsRaw(bool useNullSafety) => baseType._treatAsRaw(useNullSafety);
+  bool _treatAsRaw(bool useLegacySubtyping) =>
+      baseType._treatAsRaw(useLegacySubtyping);
 
   @override
   bool get containsTypeVariables => baseType.containsTypeVariables;
@@ -359,7 +357,7 @@ class InterfaceType extends DartType {
   }
 
   @override
-  bool _isStrongTop(bool useNullSafety) => useNullSafety ? false : isObject;
+  bool _isTop(bool useLegacySubtyping) => useLegacySubtyping && isObject;
 
   @override
   bool get isObject =>
@@ -380,9 +378,9 @@ class InterfaceType extends DartType {
   }
 
   @override
-  bool _treatAsRaw(bool useNullSafety) {
+  bool _treatAsRaw(bool useLegacySubtyping) {
     for (DartType type in typeArguments) {
-      if (!type._isTop(useNullSafety)) return false;
+      if (!type._isTop(useLegacySubtyping)) return false;
     }
     return true;
   }
@@ -567,7 +565,7 @@ class VoidType extends DartType {
   }
 
   @override
-  bool _isStrongTop(bool useNullSafety) => true;
+  bool _isStrongTop(bool useLegacySubtyping) => true;
 
   @override
   R accept<R, A>(DartTypeVisitor<R, A> visitor, A argument) =>
@@ -597,7 +595,7 @@ class DynamicType extends DartType {
   }
 
   @override
-  bool _isStrongTop(bool useNullSafety) => true;
+  bool _isStrongTop(bool useLegacySubtyping) => true;
 
   @override
   R accept<R, A>(DartTypeVisitor<R, A> visitor, A argument) =>
@@ -627,7 +625,7 @@ class ErasedType extends DartType {
   }
 
   @override
-  bool _isStrongTop(bool useNullSafety) => true;
+  bool _isStrongTop(bool useLegacySubtyping) => true;
 
   @override
   R accept<R, A>(DartTypeVisitor<R, A> visitor, A argument) =>
@@ -668,7 +666,7 @@ class AnyType extends DartType {
   }
 
   @override
-  bool _isStrongTop(bool useNullSafety) => true;
+  bool _isStrongTop(bool useLegacySubtyping) => true;
 
   @override
   R accept<R, A>(DartTypeVisitor<R, A> visitor, A argument) =>
@@ -1507,7 +1505,6 @@ class _DeferredName {
 
 class _DartTypeToStringVisitor extends DartTypeVisitor<void, void> {
   final bool _printLegacyStars;
-  final bool _useNullSafety;
   final bool _useLegacySubtyping;
   final List _fragments = []; // Strings and _DeferredNames
   bool _lastIsIdentifier = false;
@@ -1515,8 +1512,7 @@ class _DartTypeToStringVisitor extends DartTypeVisitor<void, void> {
   Map<FunctionTypeVariable, _DeferredName> _variableToName;
   Set<FunctionType> _genericFunctions;
 
-  _DartTypeToStringVisitor(
-      this._printLegacyStars, this._useNullSafety, this._useLegacySubtyping);
+  _DartTypeToStringVisitor(this._printLegacyStars, this._useLegacySubtyping);
 
   String run(DartType type) {
     _visit(type);
@@ -1668,7 +1664,7 @@ class _DartTypeToStringVisitor extends DartTypeVisitor<void, void> {
         needsComma = _comma(needsComma);
         _visit(typeVariable);
         DartType bound = typeVariable.bound;
-        if (!bound._isTop(_useNullSafety) &&
+        if (!bound._isTop(_useLegacySubtyping) &&
             (!_useLegacySubtyping || !bound.isObject)) {
           _token(' extends ');
           _visit(bound);
@@ -1749,7 +1745,7 @@ abstract class DartTypes {
 
   DartType legacyType(DartType baseType) {
     DartType result;
-    if (isTopType(baseType) ||
+    if (isStrongTopType(baseType) ||
         baseType.isNull ||
         baseType is LegacyType ||
         baseType is NullableType) {
@@ -1893,12 +1889,12 @@ abstract class DartTypes {
   /// Returns `true` if every type argument of [t] is a top type.
   // TODO(fishythefish): Should we instead check if each type argument is at its
   // bound?
-  bool treatAsRawType(DartType t) => t._treatAsRaw(useNullSafety);
+  bool treatAsRawType(DartType t) => t._treatAsRaw(useLegacySubtyping);
 
   /// Returns `true` if [t] is a top type, that is, a supertype of every type.
-  bool isTopType(DartType t) => t._isTop(useNullSafety);
+  bool isTopType(DartType t) => t._isTop(useLegacySubtyping);
 
-  bool isStrongTopType(DartType t) => t._isStrongTop(useNullSafety);
+  bool isStrongTopType(DartType t) => t._isStrongTop(useLegacySubtyping);
 
   /// Returns `true` if [s] is a subtype of [t].
   bool isSubtype(DartType s, DartType t) => _subtypeHelper(s, t);

sdk/lib/_internal/js_runtime/lib/rti.dart

@@ -1684,7 +1684,7 @@ class _Universe {
       universe, Rti baseType, String key, bool normalize) {
     if (normalize) {
       int baseKind = Rti._getKind(baseType);
-      if (isTopType(baseType) ||
+      if (isStrongTopType(baseType) ||
           isNullType(baseType) ||
           baseKind == Rti.kindQuestion ||
           baseKind == Rti.kindStar) {
@@ -2884,7 +2884,10 @@ bool isNullable(Rti t) {
       kind == Rti.kindFutureOr && isNullable(Rti._getFutureOrArgument(t));
 }
 
-bool isTopType(Rti t) => isStrongTopType(t) || isLegacyObjectType(t);
+bool isTopType(Rti t) =>
+    isStrongTopType(t) ||
+    isLegacyObjectType(t) ||
+    JS_GET_FLAG('LEGACY') && isObjectType(t);
 
 bool isStrongTopType(Rti t) {
   int kind = Rti._getKind(t);
@@ -2892,7 +2895,6 @@ bool isStrongTopType(Rti t) {
       kind == Rti.kindVoid ||
       kind == Rti.kindAny ||
       kind == Rti.kindErased ||
-      !JS_GET_FLAG('NNBD') && isObjectType(t) ||
       isNullableObjectType(t);
 }
 

sdk_nnbd/lib/_internal/js_runtime/lib/rti.dart

@@ -1778,7 +1778,7 @@ class _Universe {
       Object? universe, Rti baseType, String key, bool normalize) {
     if (normalize) {
       int baseKind = Rti._getKind(baseType);
-      if (isTopType(baseType) ||
+      if (isStrongTopType(baseType) ||
           isNullType(baseType) ||
           baseKind == Rti.kindQuestion ||
           baseKind == Rti.kindStar) {
@@ -2980,7 +2980,10 @@ bool isNullable(Rti t) {
       kind == Rti.kindFutureOr && isNullable(Rti._getFutureOrArgument(t));
 }
 
-bool isTopType(Rti t) => isStrongTopType(t) || isLegacyObjectType(t);
+bool isTopType(Rti t) =>
+    isStrongTopType(t) ||
+    isLegacyObjectType(t) ||
+    JS_GET_FLAG('LEGACY') && isObjectType(t);
 
 bool isStrongTopType(Rti t) {
   int kind = Rti._getKind(t);
@@ -2988,7 +2991,6 @@ bool isStrongTopType(Rti t) {
       kind == Rti.kindVoid ||
       kind == Rti.kindAny ||
       kind == Rti.kindErased ||
-      !JS_GET_FLAG('NNBD') && isObjectType(t) ||
       isNullableObjectType(t);
 }
 

tests/compiler/dart2js/generic_methods/function_type_variable_test.dart

@@ -73,7 +73,6 @@ main() {
 
     String printType(DartType type) => type.toStructuredText(
         printLegacyStars: options.printLegacyStars,
-        useNullSafety: options.useNullSafety,
         useLegacySubtyping: options.useLegacySubtyping);
 
     List<String> printTypes(List<DartType> types) =>