From 84344e0b7503fe15723577b81997dd9c607cbfc2 Mon Sep 17 00:00:00 2001
From: Jett Jones <jjones@panopto.com>
Date: Sat, 13 Mar 2021 12:08:51 -0800
Subject: [PATCH] #256 - Process substitution overrides in order

---
 pyhocon/config_parser.py    | 11 ++++++++++-
 pyhocon/config_tree.py      |  3 +++
 tests/test_config_parser.py | 14 ++++++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/pyhocon/config_parser.py b/pyhocon/config_parser.py
index 9241de87..3297dd83 100644
--- a/pyhocon/config_parser.py
+++ b/pyhocon/config_parser.py
@@ -619,9 +619,10 @@ def _do_substitute(cls, substitution, resolved_value, is_optional_resolved=True)
                 if transformation is None and not is_optional_resolved \
                 else transformation
 
+            # When the result is None, remove the key.
             if result is None and config_values.key in config_values.parent:
                 del config_values.parent[config_values.key]
-            else:
+            elif result is not None:
                 config_values.parent[config_values.key] = result
                 s = cls._find_substitutions(result)
                 if s:
@@ -670,6 +671,12 @@ def resolve_substitutions(cls, config, accept_unresolved=False):
                 _substitutions = substitutions[:]
 
                 for substitution in _substitutions:
+                    # If this substitution is an override, and the parent is still being processed,
+                    # skip this entry, it will be processed on the next loop.
+                    if substitution.parent.overriden_value:
+                        if substitution.parent.overriden_value in [s.parent for s in substitutions]:
+                            continue
+
                     is_optional_resolved, resolved_value = cls._resolve_variable(config, substitution)
 
                     # if the substitution is optional
@@ -695,6 +702,8 @@ def resolve_substitutions(cls, config, accept_unresolved=False):
 
                     unresolved, new_substitutions, result = cls._do_substitute(substitution, resolved_value, is_optional_resolved)
                     any_unresolved = unresolved or any_unresolved
+                    # Detected substitutions may already be listed to process
+                    new_substitutions = [n for n in new_substitutions if n not in substitutions]
                     substitutions.extend(new_substitutions)
                     if not isinstance(result, ConfigValues):
                         substitutions.remove(substitution)
diff --git a/pyhocon/config_tree.py b/pyhocon/config_tree.py
index 511fc1ce..ac6dabc8 100644
--- a/pyhocon/config_tree.py
+++ b/pyhocon/config_tree.py
@@ -473,9 +473,12 @@ def has_substitution(self):
         return len(self.get_substitutions()) > 0
 
     def get_substitutions(self):
+        # Returns a list of ConfigSubstitution tokens, in string order
         lst = []
         node = self
         while node:
+            # walking up the override chain and append overrides to the front.
+            # later, parent overrides will be processed first, followed by children
             lst = [token for token in node.tokens if isinstance(token, ConfigSubstitution)] + lst
             if hasattr(node, 'overriden_value'):
                 node = node.overriden_value
diff --git a/tests/test_config_parser.py b/tests/test_config_parser.py
index a33e8029..d3d8630a 100644
--- a/tests/test_config_parser.py
+++ b/tests/test_config_parser.py
@@ -1427,6 +1427,20 @@ def test_substitution_flat_override(self):
         assert config['database.name'] == 'peopledb'
         assert config['database.pass'] == 'peoplepass'
 
+    def test_substitution_multiple_override(self):
+        config = ConfigFactory.parse_string(
+            """
+            a: 1
+            b: foo
+            c: ${a} ${b}
+            c: ${b} ${a}
+            d: ${a} ${b}
+            d: ${a} bar
+            """)
+
+        assert config['c'] == 'foo 1'
+        assert config['d'] == '1 bar'
+
     def test_substitution_nested_override(self):
         config = ConfigFactory.parse_string(
             """