Use importlib_metadata instead of pkg_resources.

Author: whitequark

nmigen_boards/__init__.py

@@ -1,5 +1,11 @@
-import pkg_resources
 try:
-    __version__ = pkg_resources.get_distribution(__name__).version
-except pkg_resources.DistributionNotFound:
-    pass
+    try:
+        from importlib import metadata as importlib_metadata # py3.8+ stdlib
+    except ImportError:
+        import importlib_metadata # py3.7- shim
+    __version__ = importlib_metadata.version(__package__)
+except ImportError:
+    # No importlib_metadata. This shouldn't normally happen, but some people prefer not installing
+    # packages via pip at all, instead using PYTHONPATH directly or copying the package files into
+    # `lib/pythonX.Y/site-packages`. Although not a recommended way, we still try to support it.
+    __version__ = "unknown" # :nocov:

setup.py

@@ -22,6 +22,7 @@ def local_scheme(version):
     setup_requires=["wheel", "setuptools", "setuptools_scm"],
     install_requires=[
         "nmigen>=0.2,<0.4",
+        "importlib_metadata; python_version<'3.8'",
     ],
     packages=find_packages(),
     project_urls={