Partial fix for multi-method dispatch regression.

src/HLL/SerializationContextBuilder.pm

@@ -356,15 +356,24 @@ class HLL::Compiler::SerializationContextBuilder {
     # Adds a method to the meta-object, and stores an event for the action.
     # Note that methods are always subject to fixing up since the actual
     # compiled code isn't available until compilation is complete.
-    method pkg_add_method($obj, $meta_method_name, $name, $method_past) {
+    method pkg_add_method($obj, $meta_method_name, $name, $method_past, $is_dispatcher) {
         # See if we already have our compile-time dummy. If not,
         # create it.
         my $dummy;
         if pir::defined($method_past<compile_time_dummy>) {
             $dummy := $method_past<compile_time_dummy>;
         }
         else {
-            $dummy := pir::clone__PP($stub_code);
+            # What we create depends on whether it's a dispatcher or not.
+            # If it is a dispatcher, set the PMC type it uses and then use
+            # that for the dummy.
+            if $is_dispatcher {
+                $method_past.pirflags(':instanceof("DispatcherSub")');
+                $dummy := pir::assign__0PP(pir::new__Ps('DispatcherSub'), $stub_code);
+            }
+            else {
+                $dummy := pir::clone__PP($stub_code);
+            }
             pir::assign__vPS($dummy, $name);
             self.add_code($dummy);
             $method_past<compile_time_dummy> := $dummy;

src/NQP/Actions.pm

@@ -814,17 +814,14 @@ class NQP::Actions is HLL::Actions {
             my $name := ~$<private> ~ ~$<deflongname>[0].ast;
             $past.name($name);
 
-            # If it's a proto, we'll mark it as such setting the sub PMC
-            # type to DispatcherSub.
-            if $*MULTINESS eq 'proto' { $past.pirflags(':instanceof("DispatcherSub")'); }
-
             # If it is a multi, we need to build a type signature object for
             # the multi-dispatcher to use.
             if $*MULTINESS eq 'multi' { attach_multi_signature($past); }
 
             # Insert it into the method table.
             my $meta_meth := $*MULTINESS eq 'multi' ?? 'add_multi_method' !! 'add_method';
-            $*SC.pkg_add_method($*PACKAGE, $meta_meth, $name, $past);
+            my $is_dispatcher := $*MULTINESS eq 'proto';
+            $*SC.pkg_add_method($*PACKAGE, $meta_meth, $name, $past, $is_dispatcher);
 
             # Install it in the package also if needed.
             if $*SCOPE eq 'our' {

src/pmc/dispatchersub.pmc

@@ -1,5 +1,6 @@
 /* This extends the Parrot Sub PMC to add various pieces needed for
  * multiple dispatch. */
+#include "pmc_sub.h"
 pmclass DispatcherSub extends Sub auto_attrs dynpmc group nqp {
     ATTR PMC *dispatchees;     /* Used if this code object is a dispatcher. */
     ATTR PMC *dispatch_cache;  /* Holds a (multi-)dispatch cache if needed. */
@@ -20,4 +21,24 @@ pmclass DispatcherSub extends Sub auto_attrs dynpmc group nqp {
         SETATTR_DispatcherSub_dispatch_cache(interp, cloned, dispatch_cache);
         return cloned;
     }
+
+    VTABLE void assign_pmc(PMC *other) {
+        /* It's OK to assign another DispatcherSub or alternatively to
+         * assign a Parrot Sub (our immediate parent); */
+        if (other->vtable->base_type == SELF->vtable->base_type ||
+            other->vtable->base_type == enum_class_Sub) {
+            Parrot_Sub_attributes *my_sub;
+            Parrot_Sub_attributes *other_sub;
+
+            PMC_get_sub(INTERP, SELF, my_sub);
+            PMC_get_sub(INTERP, other, other_sub);
+
+            /* copy the sub struct */
+            memmove(my_sub, other_sub, sizeof (Parrot_Sub_attributes));
+        }
+        else
+            Parrot_ex_throw_from_c_args(INTERP, NULL,
+                EXCEPTION_INVALID_OPERATION,
+                "Can't assign a non-Sub type to a Sub");
+    }
 }