add tests for rakudo#2965

This will segfault until it's built on MoarVM/MoarVM#1116

t/04-nativecall/23-incomplete-types.t

@@ -0,0 +1,20 @@
+use v6;
+
+use MONKEY-SEE-NO-EVAL;
+
+use lib <lib>;
+use NativeCall :TEST;
+use Test;
+
+plan 6;
+
+for (<CUnion CStruct CPPStruct>) {
+    # test the stub case
+    my $b = (｢class Stub is repr('CStruct') { has int32 $.whatever; }
+              class Oops is repr(｣, $_, ｢) { HAS Stub $.stubby; }｣).join(｢'｣);
+    throws-like { EVAL $b }, Exception, :message ~~ /inline.*before.*definition/;
+
+    # self-inlining should fail the same way
+    my $bad = ('class Oops is repr(', $_, ') { HAS Oops $.more; }').join(｢'｣);
+    throws-like { EVAL $bad }, Exception, :message ~~ /inline.*before.*definition/;
+}