From c58677fbc75bce1bdd410307b9ff4d40571a5aa5 Mon Sep 17 00:00:00 2001
From: Nao Pross <np@0hm.ch>
Date: Tue, 2 Apr 2024 13:00:43 +0200
Subject: Create machinery to mark methods and classes as deprecated

---
 polymatrix/utils/deprecation.py | 88 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 polymatrix/utils/deprecation.py

diff --git a/polymatrix/utils/deprecation.py b/polymatrix/utils/deprecation.py
new file mode 100644
index 0000000..c9dea71
--- /dev/null
+++ b/polymatrix/utils/deprecation.py
@@ -0,0 +1,88 @@
+""" Provides tools to mark parts of code a deprecated, for a smoother
+transition to new code. """
+from __future__ import annotations
+from typing import Callable, Any, overload
+from warnings import warn
+from functools import wraps
+from abc import ABCMeta
+
+@overload
+def deprecated(alias: Callable, pending: bool = False) -> Callable:
+    """ Mark a function as deprecated, and that the function `alias` should be
+    used instead. """
+    ...
+
+@overload
+def deprecated(reason: str | None, pending: bool = False) -> Callable:
+    """ Mark a function as deprecated. """
+
+
+def deprecated(reason_or_alias, pending=False):
+    """ Mark a function or method as deprecated """
+    def decorator(fn: Callable) -> Callable:
+        if callable(reason_or_alias):
+            reason = f"{fn.__name__} has been replaced by {reason_or_alias.__name__}," \
+                + "the alias will be removed in the future"
+
+        elif isinstance(reason_or_alias, str):
+            reason = reason_or_alias
+
+        elif reason_or_alias is None:
+            reason = f"{fn.__name__} has been deprecated (no reason was provided)"
+
+        else:
+            raise TypeError(f"{reason_or_alias} must be a callable or a string!")
+
+        @wraps(fn)
+        def wrapper(*args, **kwargs):
+            w = PendingDeprecationWarning if pending else DeprecationWarning
+            warn(reason, category=w, stacklevel=2)
+            return fn(*args, **kwargs)
+
+        return wrapper
+    return decorator
+
+
+class DeprecatedMeta(type):
+    """ Metaclass to mark a class as deprecated. """
+    # Forbidden metaclass black magic adapted from
+    # https://stackoverflow.com/questions/9008444/how-to-warn-about-class-name-deprecation
+
+    def __new__(cls: type, name: str, bases: tuple[type], 
+                classdict: dict[str, Any], *args, **kwargs) -> DeprecatedMeta:
+        # Get class type that replaces the deprecated class, the "alias" class
+        alias = classdict.get("_DeprecatedClass_Alias")
+        if alias is not None:
+            warn("{} has been renamed to {}, the alias will be "
+                 "removed in the future".format(name, alias.__name__),
+                 DeprecationWarning, stacklevel=2)
+
+        # Deal with inheritance of deprecated classes. I.e. if a base class was
+        # deprecated and has an alias, replace base with alias type
+        new_bases: set[type] = set()
+
+        for b in bases:
+            base_alias = getattr(b, '_DeprecatedClass_Alias', None)
+            if base_alias is not None:
+                warn("{} has been renamed to {}, the alias will be "
+                     "removed in the future".format(b.__name__, base_alias.__name__),
+                     DeprecationWarning, stacklevel=2)
+
+            new_bases.add(base_alias or b)
+
+        # typecheker bug here? https://github.com/python/mypy/issues/12885
+        return super().__new__(cls, name, bases, classdict, *args, **kwargs) # type: ignore[misc]
+
+    def __instancecheck__(cls: type, instance: Any) -> bool:
+        return any(cls.__subclasscheck__(c)
+            for c in {type(instance), instance.__class__})
+
+    def __subclasscheck__(cls: type, subclass: type) -> bool:
+        if subclass is cls:
+            return True
+
+        return issubclass(subclass, getattr(cls, '_DeprecatedClass_Alias'))
+
+
+class DeprecatedABCMeta(DeprecatedMeta, ABCMeta):
+    """ Metaclass to mark an abstract base class as deprecated """
-- 
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