Implement QAST::Var.decl_as

Same as .decl, except clones self first. This method will let us
write declarations for QAST::Vars even if they're stored in variables,
avoiding having to duplicate :scope/:name all the time.

my $v := QAST::Var.new: :name<meow>, :scope<lexical>;
$*W.cur_lexpad[0].push: $v.decl_as: 'var';
$qast.push: $v;

Author: zoffixznet

src/QAST/Var.nqp

@@ -28,6 +28,11 @@ class QAST::Var is QAST::Node does QAST::Children {
         $!decl := $value unless $value =:= NO_VALUE;
         !nqp::isnull_s($!decl) ?? $!decl !! ""
     }
+    method decl_as($value) {
+        my $clone := nqp::clone(self);
+        $clone.decl: $value;
+        $clone;
+    }
     method slurpy($value = NO_VALUE)  { $!slurpy := $value unless $value =:= NO_VALUE; $!slurpy }
     method default($value = NO_VALUE) { $!default_or_value := $value unless $value =:= NO_VALUE; $!default_or_value }
     method value($value = NO_VALUE)   { $!default_or_value := $value unless $value =:= NO_VALUE; $!default_or_value }