Sema: Handle the edge case of in-out metatype parameter in canOpenExistentialCallArgument

Author: AnthonyLatsis

lib/Sema/OpenedExistentials.cpp

@@ -649,10 +649,11 @@ swift::canOpenExistentialCallArgument(ValueDecl *callee, unsigned paramIdx,
   if (param->isVariadic())
     return std::nullopt;
 
-  // Look through an inout and optional types on the formal type of the
-  // parameter.
+  // Look through an inout and an optional type on the parameter types.
   auto formalParamTy = param->getInterfaceType()->getInOutObjectType()
       ->lookThroughSingleOptionalType();
+  // Look through an inout and optional types on the parameter.
+  paramTy = paramTy->getInOutObjectType()->lookThroughSingleOptionalType();
 
   // If the argument is of an existential metatype, look through the
   // metatype on the parameter.
@@ -661,9 +662,6 @@ swift::canOpenExistentialCallArgument(ValueDecl *callee, unsigned paramIdx,
     paramTy = paramTy->getMetatypeInstanceType();
   }
 
-  // Look through an inout and optional types on the parameter.
-  paramTy = paramTy->getInOutObjectType()->lookThroughSingleOptionalType();
-
   // The parameter type must be a type variable.
   auto paramTypeVar = paramTy->getAs<TypeVariableType>();
   if (!paramTypeVar)

test/Constraints/opened_existentials.swift

@@ -483,3 +483,18 @@ do {
   // CHECK-NOT: open_existential_expr {{.*}} location={{.*}}:[[@LINE+1]]:{{[0-9]+}} range=
   nestedMetatypeCallee(t)
 }
+
+do {
+  protocol P {}
+
+  func foo<T: P>(_ m: inout T.Type) {}
+
+  // expected-note@+1 {{change 'let' to 'var' to make it mutable}}
+  let rValueP: P.Type
+  var lValueP: P.Type
+
+  // expected-error@+1 {{cannot pass immutable value as inout argument: 'rValueP' is a 'let' constant}}
+  foo(&rValueP)
+  // CHECK: open_existential_expr {{.*}} location={{.*}}:[[@LINE+1]]:{{[0-9]+}} range=
+  foo(&lValueP)
+}