Don't check access control for isCallableNominalType

We still want the constraint system to try looking up
a callAsFunction method even if it's inaccessible, as
we'll be able to record a fix and emit a suitable
diagnostic.

Author: hamishknight

include/swift/AST/Types.h

@@ -819,7 +819,8 @@ class alignas(1 << TypeAlignInBits) TypeBase {
   }
 
   /// Checks whether this is a type that supports being called through the
-  /// implementation of a \c callAsFunction method.
+  /// implementation of a \c callAsFunction method. Note that this does not
+  /// check access control.
   bool isCallableNominalType(DeclContext *dc);
 
   /// Retrieve the superclass of this type.

lib/Sema/TypeCheckConstraints.cpp

@@ -4575,6 +4575,7 @@ llvm::Expected<bool>
 IsCallableNominalTypeRequest::evaluate(Evaluator &evaluator, CanType ty,
                                        DeclContext *dc) const {
   auto options = defaultMemberLookupOptions;
+  options |= NameLookupFlags::IgnoreAccessControl;
   if (isa<AbstractFunctionDecl>(dc))
     options |= NameLookupFlags::KnownPrivate;
 

test/Sema/call_as_function_simple.swift

@@ -219,3 +219,12 @@ func testIUOCallAsFunction(_ x: IUOCallable) {
   let _: IUOCallable = .callable(5)
   let _: IUOCallable? = .callable(5)
 }
+
+// Test access control.
+struct PrivateCallable {
+  private func callAsFunction(_ x: Int) {} // expected-note {{'callAsFunction' declared here}}
+}
+
+func testAccessControl(_ x: PrivateCallable) {
+  x(5) // expected-error {{'callAsFunction' is inaccessible due to 'private' protection level}}
+}