Avoid ParseError deprecation warning when not imported (#1094)

openff/toolkit/typing/engines/smirnoff/forcefield.py

@@ -23,7 +23,6 @@
     "SMIRNOFFVersionError",
     "SMIRNOFFAromaticityError",
     "SMIRNOFFParseError",
-    "ParseError",
     "PartialChargeVirtualSitesError",
     "ForceField",
 ]
@@ -32,6 +31,7 @@
 import logging
 import os
 import pathlib
+import warnings
 from collections import OrderedDict
 from typing import List
 
@@ -49,7 +49,6 @@
 from openff.toolkit.typing.engines.smirnoff.plugins import load_handler_plugins
 from openff.toolkit.utils.exceptions import (
     ParameterHandlerRegistrationError,
-    ParseError,
     PartialChargeVirtualSitesError,
     SMIRNOFFAromaticityError,
     SMIRNOFFParseError,
@@ -64,6 +63,23 @@
     requires_package,
 )
 
+deprecated_names = ["ParseError"]
+
+
+def __getattr__(name):
+    if name in deprecated_names:
+        warnings.filterwarnings("default", category=DeprecationWarning)
+        warning_msg = f"{name} is DEPRECATED and will be removed in a future release of the OpenFF Toolkit."
+        warnings.warn(warning_msg, DeprecationWarning)
+
+        if name == "ParseError":
+            from openff.toolkit.utils.exceptions import _DeprecatedParseError
+
+            return _DeprecatedParseError
+
+    raise AttributeError(f"module {__name__} has no attribute {name}")
+
+
 # =============================================================================================
 # CONFIGURE LOGGER
 # =============================================================================================