Fix self references when environment variables exist (#219)

Author: anujkumar93

pyhocon/config_parser.py

@@ -89,7 +89,7 @@ def parse_file(cls, filename, encoding='utf-8', required=True, resolve=True, unr
         :param unresolved_value: assigned value value to unresolved substitution.
         If overriden with a default value, it will replace all unresolved value to the default value.
         If it is set to to pyhocon.STR_SUBSTITUTION then it will replace the value by its substitution expression (e.g., ${x})
-        :type unresolved_value: boolean
+        :type unresolved_value: class
         :return: Config object
         :type return: Config
         """
@@ -484,13 +484,18 @@ def _fixup_self_references(cls, config, accept_unresolved=False):
                                 _, _, current_item = cls._do_substitute(substitution, value)
                     previous_item = current_item
 
-                if len(history) == 1:  # special case, when self optional referencing without existing
+                if len(history) == 1:
                     for substitution in cls._find_substitutions(previous_item):
                         prop_path = ConfigTree.parse_key(substitution.variable)
                         if len(prop_path) > 1 and config.get(substitution.variable, None) is not None:
                             continue  # If value is present in latest version, don't do anything
-                        if prop_path[0] == key and substitution.optional:
-                            cls._do_substitute(substitution, None)
+                        if prop_path[0] == key:
+                            value = os.environ.get(key)
+                            if value is not None:
+                                cls._do_substitute(substitution, value)
+                                continue
+                            if substitution.optional:  # special case, when self optional referencing without existing
+                                cls._do_substitute(substitution, None)
 
     # traverse config to find all the substitutions
     @classmethod

tests/test_config_parser.py

@@ -2106,6 +2106,26 @@ def test_string_from_environment(self):
             'string_from_env': 'value_from_environment'
         }
 
+    @mock.patch.dict(os.environ, STRING_VAR='value_from_environment')
+    def test_string_from_environment_self_ref(self):
+        config = ConfigFactory.parse_string(
+            """
+            STRING_VAR = ${STRING_VAR}
+            """)
+        assert config == {
+            'STRING_VAR': 'value_from_environment'
+        }
+
+    @mock.patch.dict(os.environ, STRING_VAR='value_from_environment')
+    def test_string_from_environment_self_ref_optional(self):
+        config = ConfigFactory.parse_string(
+            """
+            STRING_VAR = ${?STRING_VAR}
+            """)
+        assert config == {
+            'STRING_VAR': 'value_from_environment'
+        }
+
     @mock.patch.dict(os.environ, TRUE_OR_FALSE='false')
     def test_bool_from_environment(self):
         config = ConfigFactory.parse_string(