Add PEP 518 pyproject.toml.

See also commits:
 * 7fca037f (adding it)
 * 416b2531 (reverting it)
 * a2ef4cb6 (adding it)
 * 810c19dd (reverting it)

Third time's the charm?

docs/install.rst

@@ -203,7 +203,7 @@ Editable development snapshot
 
 .. |develop:first-time| replace:: To install an editable development snapshot of Amaranth for the first time, run:
 .. |develop:update| replace:: Any changes made to the ``amaranth`` directory will immediately affect any code that uses Amaranth. To update the snapshot, run:
-.. |develop:reinstall| replace:: each time the editable development snapshot is updated in case package dependencies have been added or changed. Otherwise, code using Amaranth may misbehave or crash with an ``ImportError``.
+.. |develop:reinstall| replace:: any time package dependencies may have been added or changed (notably after updating the snapshot with ``git``). Otherwise, code using Amaranth may crash because of a dependency version mismatch.
 
 .. platform-picker::
 

pyproject.toml

@@ -0,0 +1,3 @@
+[build-system]
+requires = ["wheel", "setuptools~=62.0", "setuptools_scm"]
+build-backend = "setuptools.build_meta"

setup.py

@@ -38,7 +38,6 @@ setup(
     #long_description="""TODO""",
     license="BSD",
     python_requires="~=3.7",
-    setup_requires=["wheel", "setuptools", "setuptools_scm"],
     install_requires=[
         "importlib_metadata; python_version<'3.8'",  # for __version__ and amaranth._toolchain.yosys
         "importlib_resources; python_version<'3.9'", # for amaranth._toolchain.yosys