Noncopyable: fix implicit conversion error

Implicit initializers internally have "Default" parameter ownership
specifiers, which can only happen for a noncopyable type if the decl is
synthesized, since ownership is required to be specified if it were
written in the source.

There's no reason to warn for such decls, since the user can't see it
anyway. So specifically target an explicitly written "borrowing" as
being confusing, since that's the only valid case that could happen
anyway.

resolves rdar://131546153

Author: kavon

lib/Sema/CSApply.cpp

@@ -384,10 +384,12 @@ static bool willHaveConfusingConsumption(Type type,
   case ConstraintLocator::ApplyArgToParam: {
     auto argLoc = loc->castLastElementTo<LocatorPathElt::ApplyArgToParam>();
     auto paramFlags = argLoc.getParameterFlags();
-    if (paramFlags.getOwnershipSpecifier() == ParamSpecifier::Consuming)
-      return false; // Parameter already declares 'consuming'.
+    // If the param declares borrowing, then this implicit consumption
+    // due to the conversion to pass the argument is indeed confusing.
+    if (paramFlags.getOwnershipSpecifier() == ParamSpecifier::Borrowing)
+      return true;
 
-    return true;
+    return false;
   }
 
   default:

test/Sema/moveonly_casts.swift

@@ -123,3 +123,11 @@ extension Carrot {
     let _: any Veggie & ~Copyable = self
   }
 }
+
+// rdar://131546153 (implicit consuming conversion error triggers incorrectly for implicit initializers)
+struct ImplicitInit: ~Copyable {
+  let x: NC?
+}
+func test(_ nc: consuming NC) -> ImplicitInit {
+  return .init(x: nc)
+}