fix: provide _warning code

raillabel_providerkit/_util/__init__.py

@@ -0,0 +1,2 @@
+# Copyright DB Netz AG and contributors
+# SPDX-License-Identifier: Apache-2.0

raillabel_providerkit/_util/_warning.py

@@ -0,0 +1,37 @@
+# Copyright DB Netz AG and contributors
+# SPDX-License-Identifier: Apache-2.0
+
+import logging
+import typing as t
+from io import StringIO
+
+
+class _WarningsLogger:
+
+    warnings: t.List[str] = []
+
+    def __enter__(self) -> "_WarningsLogger":
+        logger = logging.getLogger("loader_warnings")
+        warnings_stream = StringIO()
+        handler = logging.StreamHandler(warnings_stream)
+        handler.setLevel(logging.WARNING)
+        logger.addHandler(handler)
+
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        logger = logging.getLogger("loader_warnings")
+        stream = logger.handlers[-1].stream
+        stream.seek(0)
+
+        warnings_list = stream.getvalue().split("\n")
+
+        if len(warnings_list) > 0:
+            warnings_list = warnings_list[:-1]
+
+        self.warnings = warnings_list
+
+
+def _warning(message: str) -> logging.Logger:
+    """Create a loader warning."""
+    logging.getLogger("loader_warnings").warning(message)