Apply resolve paths to path values in config (#3400)

docs/source/usersguide/data.rst

@@ -30,7 +30,8 @@ responsible for specifying one or more of the following:
 Each of the above files can specified in several ways. In the Python API, a
 :ref:`runtime configuration variable <usersguide_data_runtime>`
 :data:`openmc.config` can be used to specify any of the above and is initialized
-using a set of environment variables.
+using a set of environment variables. Data configuration paths set in
+:data:`openmc.config` will be expanded to absolute paths.
 
 .. _usersguide_data_runtime:
 

openmc/config.py

@@ -60,7 +60,7 @@ class _Config(MutableMapping):
         return repr(self._mapping)
 
     def _set_path(self, key, value):
-        self._mapping[key] = p = Path(value)
+        self._mapping[key] = p = Path(value).resolve()
         if not p.exists():
             warnings.warn(f"'{value}' does not exist.")
 

tests/unit_tests/test_config.py

@@ -1,5 +1,6 @@
 from collections.abc import Mapping
 import os
+from pathlib import Path
 
 import openmc
 import pytest
@@ -34,6 +35,12 @@ def test_config_basics():
     with pytest.raises(KeyError):
         openmc.config['🐖'] = '/like/to/eat/bacon'
 
+    # ensure relative paths are expanded into absolute
+    # paths
+    chain_path = Path('./chain.xml')
+    openmc.config['chain_file'] = chain_path
+    assert openmc.config['chain_file'] == chain_path.resolve()
+
 
 def test_config_patch():
     openmc.config['cross_sections'] = '/path/to/cross_sections.xml'