fix: update boolean function to handle both string and boolean inputs correctly

Fix #442

Signed-off-by: Frost Ming <[email protected]>

Author: frostming

CHANGELOG.md

@@ -6,6 +6,10 @@
 
 - Custom encoders can now receive `_parent` and `_sort_keys` parameters to enable proper encoding of nested structures. ([#429](https://github.com/python-poetry/tomlkit/issues/429))
 
+## Fixed
+
+- Fixed `tomlkit.boolean()` API to correctly handle boolean inputs. ([#442](https://github.com/python-poetry/tomlkit/issues/442))
+
 ## [0.13.3] - 2025-06-05
 
 ### Added

tomlkit/api.py

@@ -117,9 +117,9 @@ def float_(raw: str | float) -> Float:
     return item(float(raw))
 
 
-def boolean(raw: str) -> Bool:
+def boolean(raw: str | bool) -> Bool:
     """Turn `true` or `false` into a boolean item."""
-    return item(raw == "true")
+    return item(raw == "true" if isinstance(raw, str) else raw)
 
 
 def string(