deprecate __version__ attribute (pallets#2599)

CHANGES.rst

@@ -9,6 +9,8 @@ Unreleased
 -   Use modern packaging metadata with ``pyproject.toml`` instead of ``setup.cfg``.
     :pr:`326`
 -   Use ``flit_core`` instead of ``setuptools`` as build backend.
+-   Deprecate the ``__version__`` attribute. Use feature detection, or
+    ``importlib.metadata.version("click")``, instead. :issue:`2598`
 -   ``BaseCommand`` is deprecated. ``Command`` is the base class for all
     commands. :issue:`2589`
 -   ``MultiCommand`` is deprecated. ``Group`` is the base class for all group

pyproject.toml

@@ -1,5 +1,6 @@
 [project]
 name = "click"
+version = "8.2.0.dev"
 description = "Composable command line interface toolkit"
 readme = "README.rst"
 license = {file = "LICENSE.rst"}
@@ -15,7 +16,6 @@ requires-python = ">=3.8"
 dependencies = [
     "colorama; platform_system == 'Windows'",
 ]
-dynamic = ["version"]
 
 [project.urls]
 Donate = "https://palletsprojects.com/donate"

src/click/__init__.py

@@ -69,8 +69,6 @@
 from .utils import get_text_stream as get_text_stream
 from .utils import open_file as open_file
 
-__version__ = "8.2.0.dev0"
-
 
 def __getattr__(name: str) -> object:
     import warnings
@@ -108,4 +106,17 @@ def __getattr__(name: str) -> object:
         )
         return _OptionParser
 
+    if name == "__version__":
+        import importlib.metadata
+        import warnings
+
+        warnings.warn(
+            "The '__version__' attribute is deprecated and will be removed in"
+            " Click 9.1. Use feature detection or"
+            " 'importlib.metadata.version(\"click\")' instead.",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        return importlib.metadata.version("click")
+
     raise AttributeError(name)