Improve error handling of from xml conversions, both in GMSO and ffutils

gmso/core/forcefield.py

@@ -7,6 +7,7 @@
 from typing import Iterable
 
 from lxml import etree
+from pydantic import ValidationError
 
 from gmso.core.element import element_by_symbol
 from gmso.exceptions import (
@@ -573,7 +574,7 @@ def xml_from_forcefield_utilities(cls, filename):
         try:
             loader = GMSOFFs()
             ff = loader.load(filename).to_gmso_ff()
-        except (ForceFieldParseError, FileNotFoundError):
+        except (ForceFieldParseError, FileNotFoundError, ValidationError):
             loader = FoyerFFs()
             ff = loader.load(filename).to_gmso_ff()
         return ff

gmso/external/convert_foyer_xml.py

@@ -8,7 +8,7 @@
 
 
 @deprecate_function(
-    "Converting directly to GMSO XML from Foyer XML is deprecated."
+    "The `from_foyer_xml` method will be deprecated soon. Please use the package `forcefield-utilities.FoyerFFs`."
 )
 def from_foyer_xml(
     foyer_xml, gmso_xml=None, overwrite=False, validate_foyer=False

gmso/tests/test_xml_handling.py

@@ -104,7 +104,11 @@ def test_load_write_xmls_ffutils_backend(self, xml):
 
     def test_xml_error_handling(self):
         """Validate bad xml formatting in xmls."""
-        pass
+        file_path = "dummy_name.xml"
+        with pytest.raises(FileNotFoundError):
+            ForceField(file_path)
+        with pytest.raises(IndexError):
+            ForceField(get_path("empty_foyer.xml"))
 
     def test_kb_in_ffutils(self):
         xml_path = get_path("ff-example0.xml")

gmso/utils/decorators.py

@@ -85,7 +85,7 @@ def _inner(*args, **kwargs):
 
 
 def deprecate_function(msg, klass=PendingDeprecationWarning):
-    """Raise a warning that a given function is deprecated."""
+    """Raise a warning that a given function will be deprecated soon."""
 
     def decorator(func):
         @functools.wraps(func)

gmso/utils/ff_utils.py

@@ -314,10 +314,25 @@ def _validate_schema(xml_path_or_etree, schema=None):
         ff_xml = etree.parse(xml_path_or_etree)
     try:
         xml_schema.assertValid(ff_xml)
-    except:
-        raise ForceFieldParseError(
-            f"xml scheme {xml_schema} has invalid elements. Check the sections of the file."
-        )
+    except etree.DocumentInvalid as ex:
+        message = ex.error_log.last_error.message
+        line = ex.error_log.last_error.line
+        # rewrite error message for constraint violation
+        if ex.error_log.last_error.type_name == "SCHEMAV_CVC_IDC":
+            for keyword in error_texts:
+                if keyword in message:
+                    atomtype = message[
+                        message.find("[") + 1 : message.find("]")
+                    ]
+                    error_text = error_texts[keyword].format(atomtype, line)
+                    raise ForceFieldParseError((error_text, ex, line))
+                else:
+                    raise ForceFieldParseError(
+                        "Unhandled XML validation error. "
+                        "Please consider submitting a bug report.",
+                        ex,
+                        line,
+                    )
     return ff_xml