Parse incoming XML instead of using regex to get name

The parsed XML will be useful for future features.

Also change domain name handling. Allow specifying from either xml or
the `name` parameter, but raise an error if they're both present and
not equal.

plugins/modules/virt.py

@@ -155,7 +155,12 @@
 else:
     HAS_VIRT = True
 
-import re
+try:
+    from lxml import etree
+except ImportError:
+    HAS_XML = False
+else:
+    HAS_XML = True
 
 from ansible.module_utils.basic import AnsibleModule
 from ansible.module_utils._text import to_native
@@ -476,14 +481,29 @@ def handle_define(module: AnsibleModule, v: Virt):
     autostart = module.params.get('autostart', None)
 
     if not xml:
-        module.fail_json(msg="define requires xml argument")
-    if guest:
-        # there might be a mismatch between guest 'name' in the module and in the xml
-        module.warn("'xml' is given - ignoring 'name'")
+        module.fail_json(msg="define requires 'xml' argument")
     try:
-        domain_name = re.search('<name>(.*)</name>', xml).groups()[0]
-    except AttributeError:
-        module.fail_json(msg="Could not find domain 'name' in xml")
+        incoming_xml = etree.fromstring(xml)
+    except etree.XMLSyntaxError:
+        # TODO: provide info from parser
+        module.fail_json(msg="given XML is invalid")
+
+    # We'll support supplying the domain's name either from 'name' parameter or xml
+    #
+    # But we will fail if both are defined and not equal.
+    domain_name = incoming_xml.findtext("./name")
+    if domain_name is not None:
+        if guest is not None and domain_name != guest:
+            module.fail_json("given 'name' parameter does not match name in XML")
+    else:
+        if guest is None:
+            module.fail_json("missing 'name' parameter and no name provided in XML")
+        domain_name = guest
+        # since there's no <name> in the xml, we'll add it
+        etree.SubElement(incoming_xml, 'name').text = domain_name
+
+    if domain_name == '':
+        module.fail_json(msg="domain name cannot be an empty string")
 
     res = dict()
 
@@ -641,7 +661,14 @@ def main():
     )
 
     if not HAS_VIRT:
-        module.fail_json(msg='The `libvirt` module is not importable. Check the requirements.')
+        module.fail_json(
+            msg='The `libvirt` module is not importable. Check the requirements.'
+        )
+
+    if not HAS_XML:
+        module.fail_json(
+            msg='The `lxml` module is not importable. Check the requirements.'
+        )
 
     rc = VIRT_SUCCESS
     try: