Rely on backend build path and bootstrap metadata to easily build from source

MANIFEST.in

@@ -15,4 +15,3 @@ include launcher.c
 include msvc-build-launcher.cmd
 include pytest.ini
 include tox.ini
-exclude pyproject.toml  # Temporary workaround for #1644.

bootstrap.egg-info/PKG-INFO

@@ -0,0 +1,2 @@
+Name: setuptools-bootstrap
+Version: 1.0

bootstrap.egg-info/entry_points.txt

@@ -0,0 +1,14 @@
+[distutils.commands]
+egg_info = setuptools.command.egg_info:egg_info
+
+[distutils.setup_keywords]
+include_package_data = setuptools.dist:assert_bool
+install_requires = setuptools.dist:check_requirements
+extras_require = setuptools.dist:check_extras
+entry_points = setuptools.dist:check_entry_points
+
+[egg_info.writers]
+PKG-INFO = setuptools.command.egg_info:write_pkg_info
+dependency_links.txt = setuptools.command.egg_info:overwrite_arg
+entry_points.txt = setuptools.command.egg_info:write_entries
+requires.txt = setuptools.command.egg_info:write_requirements

changelog.d/2582.breaking.rst

@@ -0,0 +1 @@
+Simplified build-from-source story by providing bootstrapping metadata in a separate egg-info directory. Build requirements no longer include setuptools itself. Sdist once again includes the pyproject.toml. Project can no longer be installed from source on pip 19.x, but install from source is still supported on pip < 19 and pip >= 20 and install from wheel is still supported with pip >= 9.

pyproject.toml

@@ -1,6 +1,5 @@
 [build-system]
 requires = [
-    "setuptools >= 40.8",
     "wheel",
 ]
 build-backend = "setuptools.build_meta"

setup.cfg

@@ -41,7 +41,7 @@ exclude =
 testing =
 	# upstream
 	pytest >= 3.5, !=3.7.3
-	pytest-checkdocs >= 1.2.3
+	pytest-checkdocs >= 2.4
 	pytest-flake8
 	pytest-black >= 0.3.7; python_implementation != "PyPy"
 	pytest-cov

setuptools/tests/test_virtualenv.py

@@ -1,6 +1,7 @@
 import glob
 import os
 import sys
+import itertools
 
 import pathlib
 
@@ -65,20 +66,29 @@ def _get_pip_versions():
             # No network, disable most of these tests
             network = False
 
+    def mark(param, *marks):
+        if not isinstance(param, type(pytest.param(''))):
+            param = pytest.param(param)
+        return param._replace(marks=param.marks + marks)
+
+    def skip_network(param):
+        return param if network else mark(param, pytest.mark.skip(reason="no network"))
+
     network_versions = [
         'pip==9.0.3',
         'pip==10.0.1',
         'pip==18.1',
-        'pip==19.0.1',
+        mark('pip==19.3.1', pytest.mark.xfail(reason='pypa/pip#6599')),
+        'pip==20.0.2',
         'https://github.com/pypa/pip/archive/master.zip',
     ]
 
-    versions = [None] + [
-        pytest.param(v, **({} if network else {'marks': pytest.mark.skip}))
-        for v in network_versions
-    ]
+    versions = itertools.chain(
+        [None],
+        map(skip_network, network_versions)
+    )
 
-    return versions
+    return list(versions)
 
 
 @pytest.mark.parametrize('pip_version', _get_pip_versions())