variants: Allow multiple explicit optional variants

When a variant has optional, it is possible to explictly list it in the
XML file and add extra groups. However, the original DTD did not allow
multiple variants with `id="optional"` as `id` attribute has to be
globally unique. This patch changes its type to `CDATA`, which has less
restrictions. This also means we can no longer define `<ref>` as
`IDREF` and instead check the existence of referenced variant in parser.

Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/wrappers/variants.py

@@ -150,7 +150,11 @@ class VariantsXmlParser(object):
             self.add_child(optional, variant)
 
         for ref in variant_node.xpath("variants/ref/@id"):
-            child_variant = self.parse_variant_node(self.addons[ref], variant)
+            try:
+                child_variant = self.parse_variant_node(self.addons[ref], variant)
+            except KeyError:
+                raise RuntimeError("Variant %s references non-existing variant %s"
+                                   % (variant.uid, ref))
             self.add_child(child_variant, variant)
 
 # XXX: top-level optional

share/variants.dtd

@@ -2,7 +2,7 @@
 
 <!ELEMENT variant (release?,arches,groups?,environments*,variants*,buildinstallpackages?)?>
 <!ATTLIST variant
-    id ID #REQUIRED
+    id CDATA #REQUIRED
     name CDATA #REQUIRED
     type (variant|addon|optional|layered-product) #REQUIRED
     has_optional (true|false) #IMPLIED
@@ -39,7 +39,7 @@
 
 <!ELEMENT ref EMPTY>
 <!ATTLIST ref
-    id IDREF #REQUIRED
+    id CDATA #REQUIRED
 >
 
 <!ELEMENT buildinstallpackages (package)+>