util.datamapper: Deal with locally built stanzas missing xmlns

So the problem is that xmlns is not inherited when building a stanza,
and then :get_child(n, ns) with an explicit namespace does not find that
such child tags.

E.g.
local t = st.stanza("foo", { xmlns = "urn:example:bar" })
	:text_tag("hello", "world");
assert(t:get_child("hello", "urn:example:bar"), "This fails");

Meanwhile, during parsing (util.xmppstream or util.xml) child tags do
get the parents xmlns when not overriding them.

Thus, in the above example, if the stanza is passed trough
`t = util.xml.parse(tostring(t))` then the assert succeeds.

This change makes it so that it leaves out the namespace argument to
:get_child when it is the same as the current/parent namespace, which
behaves the same for both built and parsed stanzas.

spec/util_datamapper_spec.lua

@@ -1,7 +1,9 @@
+local st
 local xml
 local map
 
 setup(function()
+	st = require "util.stanza";
 	xml = require "util.xml";
 	map = require "util.datamapper";
 end);
@@ -160,6 +162,32 @@ describe("util.datampper", function()
 			assert.same(disco, map.parse(disco_schema, disco_info));
 		end);
 
+		it("deals with locally built stanzas", function()
+			-- FIXME this could also be argued to be a util.stanza problem
+			local ver_schema = {
+				type = "object";
+				xml = {name = "iq"};
+				properties = {
+					type = {type = "string"; xml = {attribute = true}};
+					id = {type = "string"; xml = {attribute = true}};
+					version = {
+						type = "object";
+						xml = {name = "query"; namespace = "jabber:iq:version"};
+						properties = {name = "string"; version = "string"; os = "string"};
+					};
+				};
+			};
+			local ver_st = st.iq({type = "result"; id = "v1"})
+				:query("jabber:iq:version")
+					:text_tag("name", "Prosody")
+					:text_tag("version", "trunk")
+					:text_tag("os", "Lua 5.3")
+				:reset();
+
+			local data = {type = "result"; id = "v1"; version = {name = "Prosody"; version = "trunk"; os = "Lua 5.3"}}
+			assert.same(data, map.parse(ver_schema, ver_st));
+		end);
+
 	end);
 
 	describe("unparse", function()

teal-src/util/datamapper.tl

@@ -61,7 +61,7 @@ local function unpack_propschema( propschema : schema_t, propname : string, curr
 	local proptype : json_type_name = "string"
 	local value_where : value_goes = propname and "in_text_tag" or "in_text"
 	local name = propname
-	local namespace = current_ns
+	local namespace : string
 	local prefix : string
 	local single_attribute : string
 	local enums : { any }
@@ -82,7 +82,7 @@ local function unpack_propschema( propschema : schema_t, propname : string, curr
 			if xml.name then
 				name = xml.name
 			end
-			if xml.namespace then
+			if xml.namespace and xml.namespace ~= current_ns then
 				namespace = xml.namespace
 			end
 			if xml.prefix then
@@ -137,7 +137,7 @@ local function extract_value (s : st.stanza_t, value_where : value_goes, proptyp
 		local attr = name
 		if prefix then
 			attr = prefix .. ':' .. name
-		elseif namespace ~= s.attr.xmlns then
+		elseif namespace and namespace ~= s.attr.xmlns then
 			attr = namespace .. "\1" .. name
 		end
 		return s.attr[attr]
@@ -250,7 +250,7 @@ local function unparse_property(out : st.stanza_t, v : any, proptype : json_type
 		local attr = name
 		if prefix then
 			attr = prefix .. ':' .. name
-		elseif namespace ~= current_ns then
+		elseif namespace and namespace ~= current_ns then
 			attr = namespace .. "\1" .. name
 		end
 
@@ -261,7 +261,7 @@ local function unparse_property(out : st.stanza_t, v : any, proptype : json_type
 		assert(single_attribute)
 		local propattr : { string : string } = {}
 
-		if namespace ~= current_ns then
+		if namespace and namespace ~= current_ns then
 			propattr.xmlns = namespace
 		end
 

util/datamapper.lua

@@ -29,7 +29,7 @@ local function unpack_propschema(propschema, propname, current_ns)
 	local proptype = "string"
 	local value_where = propname and "in_text_tag" or "in_text"
 	local name = propname
-	local namespace = current_ns
+	local namespace
 	local prefix
 	local single_attribute
 	local enums
@@ -50,7 +50,7 @@ local function unpack_propschema(propschema, propname, current_ns)
 			if xml.name then
 				name = xml.name
 			end
-			if xml.namespace then
+			if xml.namespace and xml.namespace ~= current_ns then
 				namespace = xml.namespace
 			end
 			if xml.prefix then
@@ -105,7 +105,7 @@ local function extract_value(s, value_where, proptype, name, namespace, prefix,
 		local attr = name
 		if prefix then
 			attr = prefix .. ":" .. name
-		elseif namespace ~= s.attr.xmlns then
+		elseif namespace and namespace ~= s.attr.xmlns then
 			attr = namespace .. "\1" .. name
 		end
 		return s.attr[attr]
@@ -218,7 +218,7 @@ local function unparse_property(out, v, proptype, propschema, value_where, name,
 		local attr = name
 		if prefix then
 			attr = prefix .. ":" .. name
-		elseif namespace ~= current_ns then
+		elseif namespace and namespace ~= current_ns then
 			attr = namespace .. "\1" .. name
 		end
 
@@ -229,7 +229,7 @@ local function unparse_property(out, v, proptype, propschema, value_where, name,
 		assert(single_attribute)
 		local propattr = {}
 
-		if namespace ~= current_ns then
+		if namespace and namespace ~= current_ns then
 			propattr.xmlns = namespace
 		end