direct-c-ffi: Invalid return type default for %call-c-function signature specification

[waywardmonkeys]

Doing (note the => ()):

  %call-c-function("exit")
    (status :: <raw-c-signed-int>) => ()
    (integer-as-raw(3))
  end;

Will result in a compile time error:

_build/build/test/test.c:146:8: error: unknown type name 'KLobjectGVKd'; did
you mean '_KLobjectGVKd'?
extern KLobjectGVKd exit (int);
       ^~~~~~~~~~~~
       _KLobjectGVKd
_build/build/test/test.c:29:3: note: '_KLobjectGVKd' declared here
} _KLobjectGVKd;
  ^
1 error generated.

To get that to compile, you need to do the non-intuitive:

  %call-c-function("exit")
    (status :: <raw-c-signed-int>) => (nothing :: <raw-c-void>)
    (integer-as-raw(3))
  end;

[waywardmonkeys]

I've tried to fix this by improving some code when generating the C:

--- a/sources/dfmc/c-back-end/c-emit-c-computation.dylan
+++ b/sources/dfmc/c-back-end/c-emit-c-computation.dylan
@@ -59,7 +59,7 @@ define method emit-primitive-call
     (b :: <c-back-end>, s :: <stream>, d :: <integer>,
      c :: <primitive-call>, f :: <&objc-msgsend>)
   let sig-values = f.primitive-signature.^signature-values;
-  let return-type = first(sig-values, default: dylan-value(#"<object>"));
+  let return-type = first(sig-values, default: dylan-value(#"<raw-c-void>"));
   format-emit(b, s, d, "((^(*)(", return-type);
   for (type in f.c-signature.^signature-required,
        first? = #t then #f)
diff --git a/sources/dfmc/c-linker/c-link-c-object.dylan b/sources/dfmc/c-linker/c-link-c-object.dylan
index 64debbb..e1bbdcb 100644
--- a/sources/dfmc/c-linker/c-link-c-object.dylan
+++ b/sources/dfmc/c-linker/c-link-c-object.dylan
@@ -34,7 +34,7 @@ define method emit-forward
     (back-end :: <c-back-end>, stream :: <stream>, o :: <&c-function>) => ();
   unless(member?(o.binding-name, $generic-names-not-to-emit, test: \=))
     let sig-values = o.primitive-signature.^signature-values;
-    let return-type = first(sig-values, default: dylan-value(#"<object>"));
+    let return-type = first(sig-values, default: dylan-value(#"<raw-c-void>"));
     if (target-os-name() == #"win32")
       format-emit*(back-end, stream, "~ ^ ~ ^ ",
                   if (o.binding-name) "extern" else "typedef" end,

But that doesn't actually address the issue.

I suspect that it may have to be dealt with at parse time. The code involved there is parse-variables-list, parse-values-list and parse-signature-as from sources/dfmc/definitions/parse-signatures.dylan which is called from parse-primitive-signature in sources/dfmc/conversion/convert-c-ffi.dylan