Fix RFC compliance of identityref value types

The current code is not compliant to Netconf RFC - RFC6020
https://datatracker.ietf.org/doc/html/rfc6020#section-9.10.5
Also restconf is not compliant to a similar RFC - RFC7951
https://datatracker.ietf.org/doc/html/rfc7951#section-6.8

This change fixes the XML generation tool pyang-apteryx-xml.py to
generate enough information so that Netconf and Restconf can
set identyref type values with the correct reference information.

A basic model test.xml, was modified to set the new the XML
properties on a basic type.

models/test.xml

@@ -67,7 +67,7 @@
       <NODE name="animal" help="This is a list of animals">
         <NODE name="*" help="The animal entry with key name">
           <NODE name="name" mode="rw" help="This is the name of the animal"/>
-          <NODE name="type" mode="rw" default="big" help="This is the type of the animal">
+          <NODE name="type" idref_href="http://test.com/ns/yang/animal-types" idref_prefix="a-types" idref_module="animal-testing-types" mode="rw" default="big" help="This is the type of the animal">
             <VALUE name="big" value="1"/>
             <VALUE name="little" value="2"/>
           </NODE>

pyang-apteryx-xml.py

@@ -315,6 +315,40 @@ def node_descendant_of(self, node, keyword):
             node = node.parent
         return False
 
+    def value_attrib_identityref(self, res, ntype):
+        if hasattr(ntype, "i_type_spec") and hasattr(ntype.i_type_spec, "idbases"):
+            for ch in ntype.i_type_spec.idbases:
+                sp_parts = ch.arg.split(':', 2);
+                if ch.i_module.i_prefixes is not None:
+                    for pref, mname in ch.i_module.i_prefixes.items():
+                        if pref == sp_parts[0]:
+                            module_name = mname[:][0]
+                            subm = ch.i_module.i_ctx.get_module(module_name)
+                            if subm is not None:
+                                    ns = subm.search_one('namespace')
+                                    if ns is not None and subm.i_prefix is not None:
+                                        res.attrib["idref_href"] = ns.arg
+                                        res.attrib["idref_prefix"] = subm.i_prefix
+                                        res.attrib["idref_module"] = module_name
+                                        return
+
+    def value_identityref(self, node, res):
+        ntype = node.search_one("type")
+        if ntype and ntype.i_typedef is not None:
+            ntype = ntype.i_typedef.search_one("type")
+        if ntype is not None:
+            if ntype.arg == "identityref":
+                self.value_attrib_identityref(res, ntype)
+            if ntype.arg == "union" and hasattr(ntype, "i_type_spec"):
+                if (hasattr(ntype.i_type_spec, "types")):
+                    base_idref = True
+                    for ch in ntype.i_type_spec.types:
+                        if ch.arg != "identityref":
+                            base_idref = False
+                            break
+                    if base_idref and hasattr(ch, "i_type_spec"):
+                        self.value_attrib_identityref(res, ch)
+
     def sample_element(self, node, parent, module, path):
         if path is None:
             return parent, module, None
@@ -335,6 +369,7 @@ def sample_element(self, node, parent, module, path):
         if node.keyword == 'rpc' or node.keyword == 'action':
             res.attrib["mode"] = "rwx"
         if node.keyword == 'leaf':
+            self.value_identityref(node, res)
             if node.i_config:
                 res.attrib["mode"] = "rw"
             elif self.node_descendant_of(node, "input"):

schema.c

@@ -3587,9 +3587,27 @@ _sch_gnode_to_json (sch_instance * instance, sch_node * schema, xmlNs *ns, GNode
     else if (APTERYX_HAS_VALUE (node))
     {
         char *value = g_strdup (APTERYX_VALUE (node) ? APTERYX_VALUE (node) : "");
+
         if (flags & SCH_F_JSON_TYPES)
         {
             value = sch_translate_to (schema, value);
+        }
+
+        if (value)
+        {
+            /* Check to see if the schema has any identityref information */
+            xmlChar *idref_module = xmlGetProp ((xmlNode *)schema, (const xmlChar *)"idref_module");
+            if (idref_module)
+            {
+                char *temp = value;
+                value = g_strdup_printf ("%s:%s", (char *) idref_module, value);
+                g_free (temp);
+                xmlFree (idref_module);
+            }
+        }
+
+        if (flags & SCH_F_JSON_TYPES)
+        {
             data = encode_json_type (schema, value);
         }
         else