implement NQPMu.{new,BUILDALL,MAGIC_BUILD}. Tests.

The latter is a hack to get attribute initialization working in classes that
don't define their own BUILD submethod.

Lack automatic BUILD calling.

src/metamodel/how/NQPMu.pm

@@ -3,8 +3,31 @@ class NQPMu {
         pir::repr_instance_of__PP(self)
     }
 
-    method new() {
-        self.CREATE()
+
+    method bless(NQPMu:U $self: *%attributes) {
+        my $instance := self.CREATE();
+        $instance.BUILDALL(|%attributes);
+        $instance
+    }
+
+    method BUILDALL(NQPMu:D $self: *%attributes) {
+        for $self.HOW.parents($self) -> $class {
+            $self.BUILD_MAGIC($class, |%attributes);
+        }
+    }
+
+    method BUILD_MAGIC(NQPMu:D $self: $type, *%attributes) {
+        for $type.HOW.attributes($type, :local) {
+            my $name := $_.name;
+            my $shortname := pir::substr($name, 2);
+            if pir::exists(%attributes, $shortname) {
+                pir::setattribute__vPPsP($self, $type, $name, %attributes{$shortname});
+            }
+        }
+    }
+
+    method new(*%attributes) {
+        self.bless(|%attributes);
     }
 
     proto method Str() is parrot_vtable('get_string') { * }

t/nqp/57-construction.t

@@ -0,0 +1,16 @@
+plan(2);
+
+class Parent {
+    has $!bar;
+
+    method bar() { $!bar }
+}
+class A is Parent {
+    has @!foo;
+
+    method foo() { @!foo }
+}
+
+my $x := A.bless(foo => [1, 2, 3], bar => 'BARBAR');
+ok(pir::join('|', $x.foo) eq '1|2|3', '.new() initializes child class attribute');
+ok($x.bar eq 'BARBAR', '.new() initializes parent class attribute');