Add deprecation notice for NamespacePackageEncountered

AUTHORS.rst

@@ -10,3 +10,4 @@ Authors
 * Shane Smiskol - https://github.com/sshane
 * Andreas Rammhold - https://github.com/andir
 * Nicholas Bunn - https://github.com/NicholasBunn
+* Nathan McDougall - https://github.com/nathanjmcdougall

CHANGELOG.rst

@@ -3,8 +3,9 @@ Changelog
 =========
 
 latest
-----------------
+------
 
+* Deprecate the `NamespacePackageEncountered` exception.
 * Improve contribution experience for Windows developers using Just.
 
 3.14 (2025-12-10)

src/grimp/exceptions.py

@@ -1,3 +1,13 @@
+import warnings
+
+
+def __getattr__(name: str):
+    if name == "NamespacePackageEncountered":
+        _NamespacePackageEncountered._warn_deprecated()
+        return _NamespacePackageEncountered
+    raise AttributeError
+
+
 class GrimpException(Exception):
     """
     Base exception for all custom Grimp exceptions to inherit.
@@ -16,14 +26,22 @@ class NoSuchContainer(GrimpException):
     """
 
 
-class NamespacePackageEncountered(GrimpException):
+class _NamespacePackageEncountered(GrimpException):
     """
-    Indicates that there was no __init__.py at the top level.
-
-    This indicates a namespace package (see PEP 420), which is not currently supported. More
-    typically this is just an oversight which can be fixed by adding the __init__.py file.
+    Deprecated.
     """
 
+    # https://github.com/python-grimp/grimp/issues/272
+    @staticmethod
+    def _warn_deprecated():
+        warnings.warn(
+            "NamespacePackageEncountered is deprecated; graphs can now be built from "
+            "namespace packages starting from Grimp 3.14. This exception will not be "
+            "raised by Grimp anymore, and will be removed in Grimp 3.16.",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+
 
 class NotATopLevelModule(GrimpException):
     """

tests/unit/test_exceptions.py

@@ -1,3 +1,5 @@
+import pytest
+
 from grimp import exceptions
 
 
@@ -54,3 +56,9 @@ def test_different_texts_are_not_equal(self):
             lineno=3,
             text="something else wrong",
         )
+
+
+class TestNamespacePackageEncountered:
+    def test_deprecated_access(self):
+        with pytest.warns(DeprecationWarning):
+            exceptions.NamespacePackageEncountered