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Tweak the subtype rule for Null

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Change-Id: I3c1f1af40f5930a02355f8d986a27db606998096
Reviewed-on: https://dart-review.googlesource.com/c/90980
Commit-Queue: Peter von der Ahé <ahe@google.com>
Reviewed-by: Dmitry Stefantsov <dmitryas@google.com>
This commit is contained in:
Peter von der Ahé 2019-01-29 10:04:21 +00:00 committed by commit-bot@chromium.org
parent 5fbf15d9c4
commit 97cb74cf63
3 changed files with 17 additions and 30 deletions
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7
pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
View file

@ -1672,12 +1672,7 @@ abstract class TypeInferrerImpl extends TypeInferrer {
/// Modifies a type as appropriate when inferring a closure return type.
DartType inferReturnType(DartType returnType) {
if (returnType == null) {
// Analyzer infers `Null` if there is no `return` expression; the spec
// says to return `void`. TODO(paulberry): resolve this difference.
return coreTypes.nullClass.rawType;
}
return returnType;
return returnType ?? typeSchemaEnvironment.nullType;
}
/// Performs type inference on the given [statement].

30
pkg/front_end/lib/src/fasta/type_inference/type_schema_environment.dart
View file

@ -151,12 +151,10 @@ class TypeSchemaEnvironment extends HierarchyBasedTypeEnvironment {
}
// SLB(bottom, T) = SLB(T, bottom) = bottom.
if (isBottom(type1)) {
return type1;
}
if (isBottom(type2)) {
return type2;
}
if (type1 is BottomType) return type1;
if (type2 is BottomType) return type2;
if (type1 == nullType) return type1;
if (type2 == nullType) return type2;
// Function types have structural lower bounds.
if (type1 is FunctionType && type2 is FunctionType) {
@ -224,12 +222,10 @@ class TypeSchemaEnvironment extends HierarchyBasedTypeEnvironment {
}
// SUB(bottom, T) = SUB(T, bottom) = T.
if (isBottom(type1)) {
return type2;
}
if (isBottom(type2)) {
return type1;
}
if (type1 is BottomType) return type2;
if (type2 is BottomType) return type1;
if (type1 == nullType) return type2;
if (type2 == nullType) return type1;
if (type1 is TypeParameterType || type2 is TypeParameterType) {
return _typeParameterStandardUpperBound(type1, type2);
@ -431,12 +427,10 @@ class TypeSchemaEnvironment extends HierarchyBasedTypeEnvironment {
}
@override
bool isBottom(DartType t) {
if (t is UnknownType) {
return true;
} else {
return super.isBottom(t);
}
bool isSubtypeOf(DartType subtype, DartType supertype) {
if (subtype is UnknownType) return true;
if (subtype == Null && supertype is UnknownType) return true;
return super.isSubtypeOf(subtype, supertype);
}
bool isEmptyContext(DartType context) {

10
pkg/kernel/lib/type_environment.dart
View file

@ -165,11 +165,6 @@ abstract class SubtypeTester {
InterfaceType getTypeAsInstanceOf(InterfaceType type, Class superclass);
/// Determines if the given type is at the bottom of the type hierarchy. May
/// be overridden in subclasses.
bool isBottom(DartType type) =>
type is BottomType || (!legacyMode && type == nullType);
/// Determines if the given type is at the top of the type hierarchy. May be
/// overridden in subclasses.
bool isTop(DartType type) =>
@ -180,7 +175,10 @@ abstract class SubtypeTester {
subtype = subtype.unalias;
supertype = supertype.unalias;
if (identical(subtype, supertype)) return true;
if (isBottom(subtype)) return true;
if (subtype is BottomType) return true;
if (subtype == nullType) {
return supertype is! BottomType;
}
if (isTop(supertype)) return true;
// Handle FutureOr<T> union type.