Enable TCH rules for slightly reducing runtime imports.

Catches typing imports that are only needed for type checking.

pyproject.toml

@@ -85,7 +85,9 @@ exclude = [
 
 [tool.ruff]
 line-length = 79
-select = ["ANN", "B", "D", "D204", "E", "F", "Q", "RUF", "SIM", "UP", "W"]
+select = [
+  "ANN", "B", "D", "D204", "E", "F", "Q", "RUF", "SIM", "TCH", "UP", "W",
+]
 ignore = [
   # Wat, type annotations for self and cls, why is this a thing?
   "ANN101",

referencing/exceptions.py

@@ -8,10 +8,10 @@
 import attrs
 
 from referencing._attrs import frozen
-from referencing.typing import URI
 
 if TYPE_CHECKING:
     from referencing import Resource
+    from referencing.typing import URI
 
 
 @frozen

referencing/retrieval.py

@@ -4,11 +4,13 @@
 from __future__ import annotations
 
 from functools import lru_cache
-from typing import Callable, TypeVar
+from typing import TYPE_CHECKING, Callable, TypeVar
 import json
 
 from referencing import Resource
-from referencing.typing import URI, D, Retrieve
+
+if TYPE_CHECKING:
+    from referencing.typing import URI, D, Retrieve
 
 #: A serialized document (e.g. a JSON string)
 _T = TypeVar("_T")