Modernize packaging-related things in Red (#5924)

setup.py

@@ -1,17 +1,64 @@
 import os
 import sys
-from setuptools import setup
+from pathlib import Path
+
+from setuptools import find_namespace_packages, setup
+
+ROOT_FOLDER = Path(__file__).parent.absolute()
+REQUIREMENTS_FOLDER = ROOT_FOLDER / "requirements"
 
 # Since we're importing `redbot` package, we have to ensure that it's in sys.path.
-sys.path.insert(0, os.path.abspath(os.path.dirname(__file__)))
+sys.path.insert(0, str(ROOT_FOLDER))
 
 from redbot import VersionInfo
 
 version, _ = VersionInfo._get_version(ignore_installed=True)
 
-if os.getenv("TOX_RED", False) and sys.version_info >= (3, 10):
-    # We want to be able to test Python versions that we do not support yet.
-    setup(python_requires=">=3.8.1", version=version)
-else:
-    # Metadata and options defined in setup.cfg
-    setup(version=version)
+
+def get_requirements(fp):
+    return [
+        line.strip()
+        for line in fp.read().splitlines()
+        if line.strip() and not line.strip().startswith("#")
+    ]
+
+
+def extras_combined(*extra_names):
+    return list(
+        {
+            req
+            for extra_name, extra_reqs in extras_require.items()
+            if not extra_names or extra_name in extra_names
+            for req in extra_reqs
+        }
+    )
+
+
+with open(REQUIREMENTS_FOLDER / "base.txt", encoding="utf-8") as fp:
+    install_requires = get_requirements(fp)
+
+extras_require = {}
+for file in REQUIREMENTS_FOLDER.glob("extra-*.txt"):
+    with file.open(encoding="utf-8") as fp:
+        extras_require[file.stem[len("extra-") :]] = get_requirements(fp)
+
+extras_require["dev"] = extras_combined()
+extras_require["all"] = extras_combined("postgres")
+
+
+python_requires = ">=3.8.1"
+if not os.getenv("TOX_RED", False) or sys.version_info < (3, 10):
+    python_requires += ",<3.10"
+
+# Metadata and options defined in pyproject.toml
+setup(
+    version=version,
+    python_requires=python_requires,
+    # TODO: use [tool.setuptools.dynamic] table once this feature gets out of beta
+    install_requires=install_requires,
+    extras_require=extras_require,
+    # TODO: use [project] table once PEP 639 gets accepted
+    license_files=["LICENSE", "redbot/**/*.LICENSE"],
+    # TODO: use [tool.setuptools.packages] table once this feature gets out of beta
+    packages=find_namespace_packages(include=["redbot", "redbot.*"]),
+)