fix: reduce number of deprecation warnings

There is (arguably) a bug in Python's warnings module, such that every
use of warnings.catch_warnings erases all memory of which warnings
have been displayed.

This breaks the "default" setting of the warnings filter which is
supposed to ensure that each warning is only displayed once per
(module, line).

So here, we disuse catch_warnings.

See https://bugs.python.org/issue29672

lektor/utils.py

@@ -8,6 +8,7 @@
 import subprocess
 import sys
 import tempfile
+import threading
 import unicodedata
 import uuid
 import warnings
@@ -19,6 +20,7 @@
 from pathlib import PurePosixPath
 from typing import Any
 from typing import Callable
+from typing import ClassVar
 from typing import Hashable
 from typing import Iterable
 from typing import overload
@@ -743,6 +745,32 @@ def __str__(self) -> str:
         return message
 
 
+class RecursionGuard(threading.local):
+    """A context manager to track recursion.
+
+    Usage:
+
+        guard = RecursionGuard()
+
+        def f(callback):
+            with guard() as call_depth:
+                if call_depth > 0:
+                    raise RuntimeError("recursion!")
+                callback()
+    """
+
+    depth = 0
+
+    @contextmanager
+    def __call__(self):
+        depth = self.depth
+        self.depth = depth + 1
+        try:
+            yield depth
+        finally:
+            self.depth = depth
+
+
 _F = TypeVar("_F", bound=Callable[..., Any])
 
 
@@ -755,6 +783,8 @@ class _Deprecate:
     version: str | None = None
     stacklevel: int = 1
 
+    _recursion_guard: ClassVar = RecursionGuard()
+
     def __call__(self, wrapped: _F) -> _F:
         if not callable(wrapped):
             raise TypeError("do not know how to deprecate {wrapped!r}")
@@ -764,10 +794,9 @@ def __call__(self, wrapped: _F) -> _F:
 
         @wraps(wrapped)
         def wrapper(*args: Any, **kwargs: Any) -> Any:
-            warnings.warn(message, stacklevel=self.stacklevel + 1)
-            with warnings.catch_warnings():
-                # ignore any of our own custom warnings generated by wrapped callable
-                warnings.simplefilter("ignore", category=DeprecatedWarning)
+            with self._recursion_guard() as call_depth:
+                if call_depth == 0:
+                    warnings.warn(message, stacklevel=self.stacklevel + 1)
                 return wrapped(*args, **kwargs)
 
         return wrapper  # type: ignore[return-value]