From cbc66f2fd6e82a376d33ff06b6d4d85b40026b30 Mon Sep 17 00:00:00 2001
From: Brian Li <me@brian14708.dev>
Date: Sat, 7 Feb 2026 17:43:42 +0800
Subject: [PATCH] feat: auto-instantiate type-annotated Config subclasses

Extends Config initialization to automatically instantiate subclasses
declared via type annotations (e.g., sub: SubConfig), not just direct
assignments (e.g., sub = SubConfig).

Type Safety Benefits:
- 'sub = SubConfig' assigns the class itself, making type checkers infer
  type[SubConfig] (the class), breaking autocomplete and type checking
- 'sub: SubConfig' declares an instance annotation, allowing type checkers
  to correctly infer SubConfig (an instance) for proper IDE support
- This commit makes the type-safe pattern work at runtime
---
 configurize/config.py | 21 +++++++++++++++++++++
 tests/test_config.py  | 28 ++++++++++++++++++----------
 2 files changed, 39 insertions(+), 10 deletions(-)

diff --git a/configurize/config.py b/configurize/config.py
index f5ad9a0..2492786 100644
--- a/configurize/config.py
+++ b/configurize/config.py
@@ -311,6 +311,7 @@ def __init__(self, **kwargs):
             )
         self._merge_args(kwargs)
 
+        # Handle assigned Config subclasses (e.g., sub = SubConfig)
         for k, v in self.items(deref=False):
             if type(v) is type and issubclass(v, Config):
                 v = v()
@@ -319,6 +320,26 @@ def __init__(self, **kwargs):
                 v._father = weakref.ref(self)
                 v._sub_cfg_name = k
 
+        # Handle type-annotated Config subclasses (e.g., sub: SubConfig)
+        annotations = self._get_class_annotations()
+        for k, annotation_type in annotations.items():
+            # Skip if already set as an attribute
+            if hasattr(self, k):
+                continue
+            # Check if the annotation is a Config subclass type
+            try:
+                if type(annotation_type) is type and issubclass(
+                    annotation_type, Config
+                ):
+                    # Instantiate the Config subclass
+                    v = annotation_type()
+                    setattr(self, k, v)
+                    v._father = weakref.ref(self)
+                    v._sub_cfg_name = k
+            except TypeError:
+                # issubclass raises TypeError if annotation_type is not a class
+                pass
+
         if self._allow_search:
             self._flatten_args = self._flatten_config()
 
diff --git a/tests/test_config.py b/tests/test_config.py
index 9ebd6a8..1c68259 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -1,5 +1,7 @@
 """Basic tests for configurize.Config"""
 
+from __future__ import annotations
+
 from configurize import Config
 from configurize.reference import Ref
 
@@ -29,25 +31,31 @@ class BaseConfig(Config):
     assert cfg.b == 2
 
 
-def test_config_references():
-    """Test using Ref to reference other config values"""
+class SubConfig(Config):
+    value = 100
+    self_ref = Ref(".value")
+    parent_ref = Ref("..base_value")
+
 
-    class SubConfig(Config):
-        value = 100
-        self_ref = Ref(".value")
-        parent_ref = Ref("..base_value")
+class ParentConfig(Config):
+    base_value = 42
+    optional: int | None
+    sub = SubConfig
+    sub2: SubConfig
 
-    class ParentConfig(Config):
-        base_value = 42
-        optional: int | None
-        sub = SubConfig
+
+def test_config_references():
+    """Test using Ref to reference other config values"""
 
     cfg = ParentConfig()
     cfg.sanity_check()
     # Test self-reference
     assert cfg.sub.self_ref == 100
+    assert cfg.sub2.self_ref == 100
     # Test parent reference
     assert cfg.sub.parent_ref == 42
+    assert cfg.sub2.parent_ref == 42
     # Verify references update when source changes
     cfg.base_value = 99
     assert cfg.sub.parent_ref == 99
+    assert cfg.sub2.parent_ref == 99