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 +1,22 @@
+use v6;
+
+use MONKEY-SEE-NO-EVAL;
+
+use lib <lib>;
+use NativeCall :TEST;
+use Test;
+
+plan 6;
+
+for (<CUnion CStruct CPPStruct>) -> $cls {
+    # test the stub case
+    my $b = (
+        "class Stub-$cls is repr('CStruct') " ~ ｢{ ... }｣,
+        "class Oops$cls" ~ ｢ is repr('｣ ~ $cls ~ ｢') { HAS Stub-｣ ~ $cls ~ ｢ $.stubby; }｣;
+    ).join("\n");
+    throws-like { EVAL $b }, Exception, :message(/inline.*before.*definition/);
+
+    # self-inlining should fail the same way
+    my $bad = ("class Oops2$cls is repr(", $cls, ') { HAS Oops2'~$cls~' $.more; }').join(｢'｣);
+    throws-like { EVAL $bad }, Exception, :message(/inline.*before.*definition/);
+}