restrict generic function type subtyping

R=leafp@google.com

Review URL: https://codereview.chromium.org/2540903003 .

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

@@ -1026,16 +1026,12 @@ class FunctionTypeImpl extends TypeImpl implements FunctionType {
     // This type cast is safe, because we checked it above.
     FunctionType s = other as FunctionType;
     if (t.typeFormals.isNotEmpty) {
-      if (s.typeFormals.isEmpty) {
-        t = instantiateToBounds(t);
-      } else {
-        List<DartType> freshVariables = relateTypeFormals(t, s, returnRelation);
-        if (freshVariables == null) {
-          return false;
-        }
-        t = t.instantiate(freshVariables);
-        s = s.instantiate(freshVariables);
+      List<DartType> freshVariables = relateTypeFormals(t, s, returnRelation);
+      if (freshVariables == null) {
+        return false;
       }
+      t = t.instantiate(freshVariables);
+      s = s.instantiate(freshVariables);
     } else if (s.typeFormals.isNotEmpty) {
       return false;
     }

pkg/analyzer/lib/src/task/strong/checker.dart

@@ -1434,15 +1434,7 @@ class _OverrideChecker {
         ]);
       }
     }
-    FunctionType concreteSubType = subType;
-    FunctionType concreteBaseType = baseType;
-    if (concreteSubType.typeFormals.isNotEmpty) {
-      if (concreteBaseType.typeFormals.isEmpty) {
-        concreteSubType = rules.instantiateToBounds(concreteSubType);
-      }
-    }
-
-    if (!rules.isOverrideSubtypeOf(concreteSubType, concreteBaseType)) {
+    if (!rules.isOverrideSubtypeOf(subType, baseType)) {
       ErrorCode errorCode;
       if (errorLocation is ExtendsClause) {
         errorCode = StrongModeCode.INVALID_METHOD_OVERRIDE_FROM_BASE;

pkg/analyzer/test/generated/type_system_test.dart

@@ -1608,7 +1608,34 @@ class StrongSubtypingTest {
     DartType u = TypeBuilder.variable("U", bound: intType);
     DartType v = TypeBuilder.variable("V", bound: u);
 
+    DartType a = TypeBuilder.variable("A");
+    DartType b = TypeBuilder.variable("B", bound: a);
+    DartType c = TypeBuilder.variable("C", bound: intType);
+    DartType d = TypeBuilder.variable("D", bound: c);
+
     _checkIsStrictSubtypeOf(
+        TypeBuilder.function(types: [s, t], required: [s], result: t),
+        TypeBuilder.function(
+            types: [a, b], required: [dynamicType], result: dynamicType));
+
+    _checkIsNotSubtypeOf(
+        TypeBuilder.function(types: [u, v], required: [u], result: v),
+        TypeBuilder.function(
+            types: [c, d], required: [objectType], result: objectType));
+
+    _checkIsNotSubtypeOf(
+        TypeBuilder.function(types: [u, v], required: [u], result: v),
+        TypeBuilder
+            .function(types: [c, d], required: [intType], result: intType));
+  }
+
+  void test_genericFunction_genericDoesNotSubtypeNonGeneric() {
+    DartType s = TypeBuilder.variable("S");
+    DartType t = TypeBuilder.variable("T", bound: s);
+    DartType u = TypeBuilder.variable("U", bound: intType);
+    DartType v = TypeBuilder.variable("V", bound: u);
+
+    _checkIsNotSubtypeOf(
         TypeBuilder.function(types: [s, t], required: [s], result: t),
         TypeBuilder.function(required: [dynamicType], result: dynamicType));
 
@@ -1616,7 +1643,7 @@ class StrongSubtypingTest {
         TypeBuilder.function(types: [u, v], required: [u], result: v),
         TypeBuilder.function(required: [objectType], result: objectType));
 
-    _checkIsStrictSubtypeOf(
+    _checkIsNotSubtypeOf(
         TypeBuilder.function(types: [u, v], required: [u], result: v),
         TypeBuilder.function(required: [intType], result: intType));
   }

pkg/analyzer/test/src/task/strong/checker_test.dart

@@ -3991,6 +3991,27 @@ void main() {
 ''');
   }
 
+  void test_universalFunctionSubtyping() {
+    checkFile(r'''
+dynamic foo<T>(dynamic x) => x;
+
+void takesDtoD(dynamic f(dynamic x)) {}
+
+void test() {
+  // here we currently infer an instantiation.
+  takesDtoD(/*pass should be error:INVALID_ASSIGNMENT*/foo);
+}
+
+class A {
+  dynamic method(dynamic x) => x;
+}
+
+class B extends A {
+  /*error:INVALID_METHOD_OVERRIDE*/T method<T>(T x) => x;
+}
+    ''');
+  }
+
   void test_voidSubtyping() {
     // Regression test for https://github.com/dart-lang/sdk/issues/25069
     checkFile('''

pkg/analyzer/test/src/task/strong/inferred_type_test.dart

@@ -2263,26 +2263,8 @@ class C {
   dynamic g(int x) => x;
 }
 class D extends C {
-  T m<T>(T x) => x;
-  T g<T>(T x) => x;
-}
-main() {
-  int y = /*info:DYNAMIC_CAST*/(/*info:UNNECESSARY_CAST*/new D() as C).m(42);
-  print(y);
-}
-  ''');
-  }
-
-  void test_genericMethods_handleOverrideOfNonGenericWithGeneric_comment() {
-    // Regression test for crash when adding genericity
-    checkFile('''
-class C {
-  m(x) => x;
-  dynamic g(int x) => x;
-}
-class D extends C {
-  /*=T*/ m/*<T>*/(/*=T*/ x) => x;
-  /*=T*/ g/*<T>*/(/*=T*/ x) => x;
+  /*error:INVALID_METHOD_OVERRIDE*/T m<T>(T x) => x;
+  /*error:INVALID_METHOD_OVERRIDE*/T g<T>(T x) => x;
 }
 main() {
   int y = /*info:DYNAMIC_CAST*/(/*info:UNNECESSARY_CAST*/new D() as C).m(42);

pkg/dev_compiler/tool/sdk_expected_errors.txt

@@ -1,5 +1,12 @@
 [error] Couldn't infer type parameter 'T'; '_ControllerEventSinkWrapper<dynamic>' must be of type 'EventSink<T>'. (dart:async/stream.dart, line 1346, col 16)
 [error] The argument type '_ControllerEventSinkWrapper' can't be assigned to the parameter type 'EventSink<T>'. (dart:async/stream.dart, line 1346, col 53)
+[error] A value of type '<R>(Zone, ZoneDelegate, Zone, () → R) → R' can't be assigned to a parameter of type '(Zone, ZoneDelegate, Zone, () → dynamic) → dynamic'. (dart:async/zone.dart, line 1071, col 51)
+[error] A value of type '<R,T>(Zone, ZoneDelegate, Zone, (T) → R, T) → R' can't be assigned to a parameter of type '(Zone, ZoneDelegate, Zone, (dynamic) → dynamic, dynamic) → dynamic'. (dart:async/zone.dart, line 1073, col 56)
+[error] A value of type '<R,T1,T2>(Zone, ZoneDelegate, Zone, (T1, T2) → R, T1, T2) → R' can't be assigned to a parameter of type '(Zone, ZoneDelegate, Zone, (dynamic, dynamic) → dynamic, dynamic, dynamic) → dynamic'. (dart:async/zone.dart, line 1075, col 57)
+[error] A value of type '<R>(Zone, ZoneDelegate, Zone, () → R) → () → R' can't be assigned to a parameter of type '(Zone, ZoneDelegate, Zone, () → dynamic) → () → dynamic'. (dart:async/zone.dart, line 1078, col 23)
+[error] A value of type '<R,T>(Zone, ZoneDelegate, Zone, (T) → R) → (T) → R' can't be assigned to a parameter of type '(Zone, ZoneDelegate, Zone, (dynamic) → dynamic) → (dynamic) → dynamic'. (dart:async/zone.dart, line 1081, col 23)
+[error] A value of type '<R,T1,T2>(Zone, ZoneDelegate, Zone, (T1, T2) → R) → (T1, T2) → R' can't be assigned to a parameter of type '(Zone, ZoneDelegate, Zone, (dynamic, dynamic) → dynamic) → (dynamic, dynamic) → dynamic'. (dart:async/zone.dart, line 1084, col 23)
+[error] A value of type '<R>(Zone, ZoneDelegate, Zone, dynamic, StackTrace) → R' can't be assigned to a parameter of type '(Zone, ZoneDelegate, Zone, dynamic, StackTrace) → dynamic'. (dart:async/zone.dart, line 1100, col 23)
 [error] Invalid override. The type of 'ChunkedConverter.bind' ('(dynamic) → dynamic') isn't a subtype of 'Converter<S, T>.bind' ('(Stream<S>) → Stream<T>'). (dart:convert/chunked_conversion.dart, line 14, col 3)
 [error] Invalid override. The type of 'ChunkedConverter.bind' ('(dynamic) → dynamic') isn't a subtype of 'StreamTransformer<S, T>.bind' ('(Stream<S>) → Stream<T>'). (dart:convert/chunked_conversion.dart, line 14, col 3)
 [error] Invalid override. The type of 'ChunkedConverter.startChunkedConversion' ('(dynamic) → dynamic') isn't a subtype of 'Converter<S, T>.startChunkedConversion' ('(Sink<T>) → Sink<S>'). (dart:convert/chunked_conversion.dart, line 15, col 3)