Implement trait_mod:<hides> and a trait_mod:<is> for is hidden, plus …

…add some attributes in ClassHOW that we'll use to track these.

src/classes/ClassHOW.pir

@@ -25,6 +25,11 @@ This class subclasses P6metaclass to give Perl 6 specific meta-class behaviors.
     $P1 = p6meta.'get_parrotclass'($P1)
     addparent $P0, $P1
 
+    # Couple of useful attributes for tracking interface consistency
+    # information.
+    addattribute $P0, '$!hides'
+    addattribute $P0, '$!hidden'
+
     # Create proto-object for it.
     classhowproto = p6meta.'register'($P0)
 
@@ -442,6 +447,39 @@ XXX Work out exactly why.
     .tailcall $P0.'WHAT'()
 .end
 
+
+=item hides
+
+Accessor for hides property.
+
+=cut
+
+.sub 'hides' :method
+    $P0 = getattribute self, '$!hides'
+    unless null $P0 goto done
+    $P0 = get_hll_global 'Array'
+    $P0 = $P0.'new'()
+    setattribute self, '$!hides', $P0
+  done:
+    .return ($P0)
+.end
+
+
+=item hidden
+
+Accessor for hidden property.
+
+=cut
+
+.sub 'hidden' :method
+    $P0 = getattribute self, '$!hidden'
+    unless null $P0 goto done
+    $P0 = new ['Perl6Scalar']
+    setattribute self, '$!hidden', $P0
+  done:
+    .return ($P0)
+.end
+
 =back
 
 =cut

src/setting/traits.pm

@@ -29,6 +29,10 @@ multi trait_mod:<is>(Class $child, Object $parent) {
     };
 }
 
+multi trait_mod:<is>(Class $child, :$hidden!) {
+    $child.hidden = True;
+}
+
 multi trait_mod:<is>(Code $block, $arg?, :$export!) {
     # Maybe we can re-write some more of this out of PIR and into Perl 6.
     Q:PIR {
@@ -142,3 +146,8 @@ multi trait_mod:<returns>(Code $block is rw, Object $type) {
 multi trait_mod:<will>($declarand, &arg, *%name) {
     &trait_mod:<is>($declarand, &arg, |%name);
 }
+
+multi trait_mod:<hides>(Class $child, Object $parent) {
+    &trait_mod:<is>($child, $parent);
+    $child.hides.push($parent)
+}