[5.9] Fix covariant erasure for constrained existential

include/swift/AST/GenericSignature.h

@@ -360,6 +360,8 @@ class alignas(1 << TypeAlignInBits) GenericSignatureImpl final
   /// Determine whether the given dependent type is required to be a class.
   bool requiresClass(Type type) const;
 
+  Type getUpperBound(Type type, bool wantDependentUpperBound = false) const;
+
   /// Determine the superclass bound on the given dependent type.
   Type getSuperclassBound(Type type) const;
 

lib/AST/GenericSignature.cpp

@@ -626,59 +626,36 @@ unsigned GenericSignatureImpl::getGenericParamOrdinal(
 }
 
 Type GenericSignatureImpl::getNonDependentUpperBounds(Type type) const {
+  return getUpperBound(type);
+}
+
+Type GenericSignatureImpl::getDependentUpperBounds(Type type) const {
+  return getUpperBound(type, /*wantDependentBound=*/true);
+}
+
+Type GenericSignatureImpl::getUpperBound(Type type,
+                                         bool wantDependentBound) const {
   assert(type->isTypeParameter());
 
   bool hasExplicitAnyObject = requiresClass(type);
 
   llvm::SmallVector<Type, 2> types;
+
   if (Type superclass = getSuperclassBound(type)) {
-    // If the class contains a type parameter, try looking for a non-dependent
-    // superclass.
-    while (superclass && superclass->hasTypeParameter()) {
-      superclass = superclass->getSuperclass();
-    }
+    do {
+      superclass = getReducedType(superclass);
+      if (wantDependentBound || !superclass->hasTypeParameter()) {
+        break;
+      }
+    } while ((superclass = superclass->getSuperclass()));
 
     if (superclass) {
       types.push_back(superclass);
       hasExplicitAnyObject = false;
     }
   }
-  for (auto *proto : getRequiredProtocols(type)) {
-    if (proto->requiresClass())
-      hasExplicitAnyObject = false;
-
-    types.push_back(proto->getDeclaredInterfaceType());
-  }
-
-  auto constraint = ProtocolCompositionType::get(
-      getASTContext(), types,
-      hasExplicitAnyObject);
-
-  if (!constraint->isConstraintType()) {
-    assert(constraint->getClassOrBoundGenericClass());
-    return constraint;
-  }
-
-  return ExistentialType::get(constraint);
-}
-
-Type GenericSignatureImpl::getDependentUpperBounds(Type type) const {
-  assert(type->isTypeParameter());
-
-  llvm::SmallVector<Type, 2> types;
-
-  auto &ctx = type->getASTContext();
-
-  bool hasExplicitAnyObject = requiresClass(type);
-
-  // FIXME: If the superclass bound is implied by one of our protocols, we
-  // shouldn't add it to the constraint type.
-  if (Type superclass = getSuperclassBound(type)) {
-    types.push_back(superclass);
-    hasExplicitAnyObject = false;
-  }
 
-  for (auto proto : getRequiredProtocols(type)) {
+  for (auto *proto : getRequiredProtocols(type)) {
     if (proto->requiresClass())
       hasExplicitAnyObject = false;
 
@@ -724,26 +701,25 @@ Type GenericSignatureImpl::getDependentUpperBounds(Type type) const {
           argTypes.push_back(reducedType);
       }
 
-      // We should have either constrained all primary associated types,
-      // or none of them.
-      if (!argTypes.empty()) {
-        if (argTypes.size() != primaryAssocTypes.size()) {
-          llvm::errs() << "Not all primary associated types constrained?\n";
-          llvm::errs() << "Interface type: " << type << "\n";
-          llvm::errs() << GenericSignature(this) << "\n";
-          abort();
-        }
-
-        types.push_back(ParameterizedProtocolType::get(ctx, baseType, argTypes));
+      // If we have constrained all primary associated types, create a
+      // parameterized protocol type. During code completion, we might call
+      // `getExistentialType` (which calls this method) on a generic parameter
+      // that doesn't have all parameters specified, e.g. to get a consise
+      // description of the parameter type to the following function.
+      //
+      // func foo<P: Publisher>(p: P) where P.Failure == Never
+      //
+      // In that case just add the base type in the default branch below.
+      if (argTypes.size() == primaryAssocTypes.size()) {
+        types.push_back(ParameterizedProtocolType::get(getASTContext(), baseType, argTypes));
         continue;
       }
     }
-
     types.push_back(baseType);
   }
 
-  auto constraint = ProtocolCompositionType::get(
-     ctx, types, hasExplicitAnyObject);
+  auto constraint = ProtocolCompositionType::get(getASTContext(), types,
+                                                 hasExplicitAnyObject);
 
   if (!constraint->isConstraintType()) {
     assert(constraint->getClassOrBoundGenericClass());

lib/Sema/CSDiagnostics.cpp

@@ -8807,6 +8807,10 @@ bool MissingExplicitExistentialCoercion::fixItRequiresParens() const {
 
 void MissingExplicitExistentialCoercion::fixIt(
     InFlightDiagnostic &diagnostic) const {
+
+  if (ErasedResultType->hasTypeParameter())
+    return;
+
   bool requiresParens = fixItRequiresParens();
 
   auto callRange = getSourceRange();

lib/Sema/CSFix.cpp

@@ -2507,6 +2507,12 @@ bool AddExplicitExistentialCoercion::isRequired(
           return Action::Stop;
         }
 
+        if (erasedMemberTy->isExistentialType() &&
+             erasedMemberTy->hasTypeParameter()) {
+          RequiresCoercion = true;
+          return Action::Stop;
+        }
+
         return Action::SkipChildren;
       }
 

lib/Sema/CSSimplify.cpp

@@ -12914,6 +12914,7 @@ ConstraintSystem::simplifyApplicableFnConstraint(
       // `as` coercion.
       if (AddExplicitExistentialCoercion::isRequired(
               *this, func2->getResult(), openedExistentials, locator)) {
+
         if (!shouldAttemptFixes())
           return SolutionKind::Error;
 

lib/Sema/ConstraintSystem.cpp

@@ -2053,10 +2053,8 @@ static bool isMainDispatchQueueMember(ConstraintLocator *locator) {
 ///
 /// \note If a 'Self'-rooted type parameter is bound to a concrete type, this
 /// routine will recurse into the concrete type.
-static Type
-typeEraseExistentialSelfReferences(
-    Type refTy, Type baseTy,
-    TypePosition outermostPosition) {
+static Type typeEraseExistentialSelfReferences(Type refTy, Type baseTy,
+                                               TypePosition outermostPosition) {
   assert(baseTy->isExistentialType());
   if (!refTy->hasTypeParameter()) {
     return refTy;
@@ -2170,7 +2168,6 @@ typeEraseExistentialSelfReferences(
       return erasedTy;
     });
   };
-
   return transformFn(refTy, outermostPosition);
 }
 
@@ -2299,16 +2296,25 @@ Type ConstraintSystem::getMemberReferenceTypeFromOpenedType(
     const auto selfGP = cast<GenericTypeParamType>(
         outerDC->getSelfInterfaceType()->getCanonicalType());
     auto openedTypeVar = replacements.lookup(selfGP);
+
     type = typeEraseOpenedExistentialReference(type, baseObjTy, openedTypeVar,
                                                TypePosition::Covariant);
 
+    Type contextualTy;
+
+    if (auto *anchor = getAsExpr(simplifyLocatorToAnchor(locator))) {
+      contextualTy =
+          getContextualType(getParentExpr(anchor), /*forConstraint=*/false);
+    }
+
     if (!hasFixFor(locator) &&
         AddExplicitExistentialCoercion::isRequired(
             *this, nonErasedResultTy,
             [&](TypeVariableType *typeVar) {
               return openedTypeVar == typeVar ? baseObjTy : Optional<Type>();
             },
-            locator)) {
+            locator) &&
+        !contextualTy) {
       recordFix(AddExplicitExistentialCoercion::create(
           *this, getResultType(type), locator));
     }

test/Constraints/opened_existentials.swift

@@ -6,6 +6,10 @@ protocol P {
   associatedtype A: Q
 }
 
+protocol P1<A> {
+  associatedtype A
+}
+
 extension Int: P {
   typealias A = Double
 }
@@ -228,6 +232,7 @@ func testTakeValueAndClosure(p: any P) {
 protocol B {
   associatedtype C: P where C.A == Double
   associatedtype D: P
+  associatedtype E: P1 where E.A == Double
 }
 
 protocol D {
@@ -242,6 +247,7 @@ extension B {
 
 func testExplicitCoercionRequirement(v: any B, otherV: any B & D) {
   func getC<T: B>(_: T) -> T.C { fatalError() }
+  func getE<T: B>(_: T) -> T.E { fatalError() }
   func getTuple<T: B>(_: T) -> (T, T.C) { fatalError() }
   func getNoError<T: B>(_: T) -> T.C.A { fatalError() }
   func getComplex<T: B>(_: T) -> ([(x: (a: T.C, b: Int), y: Int)], [Int: T.C]) { fatalError() }
@@ -252,11 +258,14 @@ func testExplicitCoercionRequirement(v: any B, otherV: any B & D) {
 
   _ = getC(v) // expected-error {{inferred result type 'any P' requires explicit coercion due to loss of generic requirements}} {{14-14=as any P}}
   _ = getC(v) as any P // Ok
-
+
+  _ = getE(v) // expected-error {{inferred result type 'any P1<Double>' requires explicit coercion due to loss of generic requirements}} {{14-14=as any P1<Double>}}
+  _ = getE(v) as any P1<Double> // Ok
+
   _ = getTuple(v) // expected-error {{inferred result type '(any B, any P)' requires explicit coercion due to loss of generic requirements}} {{18-18=as (any B, any P)}}
   _ = getTuple(v) as (any B, any P) // Ok
-
-  _ = getNoError(v) // Ok because T.C.A == Double
+  // Ok because T.C.A == Double
+  _ = getNoError(v)
 
   _ = getComplex(v) // expected-error {{inferred result type '([(x: (a: any P, b: Int), y: Int)], [Int : any P])' requires explicit coercion due to loss of generic requirements}} {{20-20=as ([(x: (a: any P, b: Int), y: Int)], [Int : any P])}}
   _ = getComplex(v) as ([(x: (a: any P, b: Int), y: Int)], [Int : any P]) // Ok
@@ -305,3 +314,58 @@ func testExplicitCoercionRequirement(v: any B, otherV: any B & D) {
   getP((getC(v) as any P))   // Ok - parens avoid opening suppression
   getP((v.getC() as any P))  // Ok - parens avoid opening suppression
 }
+
+class C1 {}
+class C2<T>: C1 {}
+
+// Test Associated Types
+protocol P2 {
+  associatedtype A
+  associatedtype B: C2<A>
+
+  func returnAssocTypeB() -> B
+}
+
+func testAssocReturn(p: any P2) {
+  let _ = p.returnAssocTypeB()  // returns C1
+}
+
+protocol Q2 : P2 where A == Int {}
+
+do {
+  let q: any Q2
+  let _ = q.returnAssocTypeB() // returns C1
+}
+
+// Test Primary Associated Types
+protocol P3<A> {
+  associatedtype A
+  associatedtype B: C2<A>
+
+  func returnAssocTypeB() -> B
+}
+
+func testAssocReturn(p: any P3<Int>) {
+  let _ = p.returnAssocTypeB() // returns C2<A>
+}
+
+func testAssocReturn(p: any P3<any P3<String>>) {
+  let _ = p.returnAssocTypeB()
+}
+
+protocol P4<A> {
+  associatedtype A
+  associatedtype B: C2<A>
+
+  func returnPrimaryAssocTypeA() -> A
+  func returnAssocTypeCollection() -> any Collection<A>
+}
+
+ //Confirm there is no way to access Primary Associated Type directly
+func testPrimaryAssocReturn(p: any P4<Int>) {
+  let _ = p.returnPrimaryAssocTypeA()
+}
+
+func testPrimaryAssocCollection(p: any P4<Float>) {
+  let _: any Collection<Float> = p.returnAssocTypeCollection()
+}

test/SILGen/existential_member_accesses_self_assoctype.swift

@@ -745,10 +745,51 @@ func testContravariantAssocMethod1Concrete(p3: any P3) {
 // CHECK: [[WITNESS:%[0-9]+]] = witness_method $@opened([[OPENED_ID]], any P3) Self, #P3.invariantAssocMethod1 : <Self where Self : P3> (Self) -> () -> GenericStruct<Self.A>
 // CHECK: [[RESULT:%[0-9]+]] = apply [[WITNESS]]<@opened([[OPENED_ID]], any P3) Self>([[OPENED]]) : $@convention(witness_method: P3) <τ_0_0 where τ_0_0 : P3> (@in_guaranteed τ_0_0) -> GenericStruct<Bool>
 // CHECK: debug_value [[RESULT]] : $GenericStruct<Bool>, let, name "x"
+// CHECK: } // end sil function '$s42existential_member_accesses_self_assoctype33testInvariantAssocMethod1Concrete2p3yAA2P3_p_tF'
 func testInvariantAssocMethod1Concrete(p3: any P3) {
   let x = p3.invariantAssocMethod1()
 }
 
+// --------------------------------------------------------------------------------------------------------
+//  Covariant dependent member type erasure in concrete dependent member type as primary associated type
+// --------------------------------------------------------------------------------------------------------
+
+class C {}
+class GenericClass<T> {}
+class GenericSubClass<T> : C {}
+
+protocol P5<A>{
+  associatedtype A
+  associatedtype B : GenericClass<A>
+  associatedtype C : GenericSubClass<A>
+
+  func returnAssocTypeB() -> B
+
+  func returnAssocTypeC() -> C
+}
+
+// CHECK-LABEL: sil hidden [ossa] @$s42existential_member_accesses_self_assoctype30testCovariantAssocGenericClass2p5AA0iJ0CySiGAA2P5_pSi1AAaGPRts_XP_tF
+// CHECK: [[OPENED:%[0-9]+]] = open_existential_addr immutable_access %0 : $*any P5<Int> to $*@opened([[OPENED_ID:"[0-9A-F-]+"]], any P5<Int>) Self
+// CHECK: [[APPLY:%[0-9]+]] = apply [[WITNESS]]<@opened([[OPENED_ID]], any P5<Int>) Self>([[OPENED]]) : $@convention(witness_method: P5) <τ_0_0 where τ_0_0 : P5> (@in_guaranteed τ_0_0) -> @owned τ_0_0.B
+// CHECK: [[UPCAST:%[0-9]+]] = upcast [[APPLY]] : $@opened([[OPENED_ID]], any P5<Int>) Self.B to $GenericClass<Int>
+// CHECK: return %{{[0-9]+}} : $GenericClass<Int>
+// CHECK: } // end sil function '$s42existential_member_accesses_self_assoctype30testCovariantAssocGenericClass2p5AA0iJ0CySiGAA2P5_pSi1AAaGPRts_XP_tF'
+func testCovariantAssocGenericClass(p5: any P5<Int>) -> GenericClass<Int> {
+  let x = p5.returnAssocTypeB()
+  return x
+}
+
+// CHECK-LABEL: sil hidden [ossa] @$s42existential_member_accesses_self_assoctype33testCovariantAssocGenericSubClass2p5AA0ijK0CySbGAA2P5_pSb1AAaGPRts_XP_tF
+// CHECK: [[OPENED:%[0-9]+]] = open_existential_addr immutable_access %0 : $*any P5<Bool> to $*@opened([[OPENED_ID:"[0-9A-F-]+"]], any P5<Bool>) Self
+// CHECK: apply %3<@opened([[OPENED_ID]], any P5<Bool>) Self>([[OPENED]]) : $@convention(witness_method: P5) <τ_0_0 where τ_0_0 : P5> (@in_guaranteed τ_0_0) -> @owned τ_0_0.C
+// CHECK: [[UPCAST:%[0-9]+]] = upcast [[APPLY:%[0-9]+]] : $@opened([[OPENED_ID]], any P5<Bool>) Self.C to $GenericSubClass<Bool>
+// CHECK: return %{{[0-9]+}} : $GenericSubClass<Bool>
+// CHECK: } // end sil function '$s42existential_member_accesses_self_assoctype33testCovariantAssocGenericSubClass2p5AA0ijK0CySbGAA2P5_pSb1AAaGPRts_XP_tF'
+func testCovariantAssocGenericSubClass(p5: any P5<Bool>) -> GenericSubClass<Bool> {
+  let y = p5.returnAssocTypeC()
+  return y
+}
+
 // -----------------------------------------------------------------------------
 //  Covariant dependent member type erasure in concrete dependent member type
 // -----------------------------------------------------------------------------

test/decl/protocol/existential_member_accesses_self_assoctype.swift

@@ -918,12 +918,24 @@ do {
   let _: Class2Base = exist.method5()
   let _: any Class2Base & CovariantAssocTypeErasure = exist.method6()
   let _: any Class2Base & CovariantAssocTypeErasure = exist.method7()
-
   let _: Any? = exist.method8()
   let _: (AnyObject, Bool) = exist.method9()
   let _: any CovariantAssocTypeErasure.Type = exist.method10()
   let _: Array<Class2Base> = exist.method11()
   let _: Dictionary<String, Class2Base> = exist.method12()
+
+  let _ = exist.method1()
+  let _ = exist.method2()
+  let _ = exist.method3()
+  let _ = exist.method4()
+  let _ = exist.method5()
+  let _ = exist.method6()
+  let _ = exist.method7()
+  let _ = exist.method8()
+  let _ = exist.method9()
+  let _ = exist.method10()
+  let _ = exist.method11()
+  let _ = exist.method12()
 }
 do {
   let exist: any CovariantAssocTypeErasureDerived