install importlib_metadata on Python < 3.8

CHANGES.rst

@@ -12,6 +12,8 @@ Unreleased
 -   Fix some types that weren't available in Python 3.6.0. :issue:`1882`
 -   Fix type checking for iterating over ``ProgressBar`` object.
     :issue:`1892`
+-   The ``importlib_metadata`` backport package is installed on Python <
+    3.8. :issue:`1889`
 
 
 Version 8.0.0

requirements/dev.txt

@@ -34,8 +34,6 @@ idna==2.10
     # via requests
 imagesize==1.2.0
     # via sphinx
-importlib-metadata==4.0.1
-    # via -r requirements/tests.in
 iniconfig==1.1.1
     # via pytest
 jinja2==2.11.3
@@ -133,8 +131,6 @@ virtualenv==20.4.6
     # via
     #   pre-commit
     #   tox
-zipp==3.4.1
-    # via importlib-metadata
 
 # The following packages are considered to be unsafe in a requirements file:
 # pip

requirements/tests.in

@@ -1,2 +1 @@
 pytest
-importlib_metadata

requirements/tests.txt

@@ -6,8 +6,6 @@
 #
 attrs==21.2.0
     # via pytest
-importlib-metadata==4.0.1
-    # via -r requirements/tests.in
 iniconfig==1.1.1
     # via pytest
 packaging==20.9
@@ -22,5 +20,3 @@ pytest==6.2.4
     # via -r requirements/tests.in
 toml==0.10.2
     # via pytest
-zipp==3.4.1
-    # via importlib-metadata

setup.py

@@ -1,3 +1,9 @@
 from setuptools import setup
 
-setup(name="click", install_requires=["colorama; platform_system == 'Windows'"])
+setup(
+    name="click",
+    install_requires=[
+        "colorama; platform_system == 'Windows'",
+        "importlib-metadata; python_version < '3.8'",
+    ],
+)

src/click/decorators.py

@@ -370,15 +370,7 @@ def callback(ctx: Context, param: Parameter, value: bool) -> None:
                 from importlib import metadata  # type: ignore
             except ImportError:
                 # Python < 3.8
-                try:
-                    import importlib_metadata as metadata  # type: ignore
-                except ImportError:
-                    metadata = None
-
-            if metadata is None:
-                raise RuntimeError(
-                    "Install 'importlib_metadata' to get the version on Python < 3.8."
-                )
+                import importlib_metadata as metadata  # type: ignore
 
             try:
                 version = metadata.version(package_name)  # type: ignore