🔥 Revert existing PEP 518 support

It might be easier to go about implementing things with a clean state.

Please don't hate mate -> takluyver.

src/pip/_internal/commands/wheel.py

@@ -180,7 +180,6 @@ def run(self, options, args):
                         finder, preparer, wheel_cache,
                         build_options=options.build_options or [],
                         global_options=options.global_options or [],
-                        no_clean=options.no_clean,
                     )
                     wheels_built_successfully = wb.build(
                         requirement_set.requirements.values(), session=session,

src/pip/_internal/req/req_install.py

@@ -435,18 +435,6 @@ def setup_py(self):
 
         return setup_py
 
-    @property
-    def pyproject_toml(self):
-        assert self.source_dir, "No source dir for %s" % self
-
-        pp_toml = os.path.join(self.setup_py_dir, 'pyproject.toml')
-
-        # Python2 __file__ should not be unicode
-        if six.PY2 and isinstance(pp_toml, six.text_type):
-            pp_toml = pp_toml.encode(sys.getfilesystemencoding())
-
-        return pp_toml
-
     def run_egg_info(self):
         assert self.source_dir
         if self.name:

src/pip/_internal/wheel.py

@@ -5,7 +5,6 @@
 
 import collections
 import compileall
-import copy
 import csv
 import hashlib
 import logging
@@ -17,9 +16,8 @@
 import warnings
 from base64 import urlsafe_b64encode
 from email.parser import Parser
-from sysconfig import get_paths
 
-from pip._vendor import pkg_resources, pytoml
+from pip._vendor import pkg_resources
 from pip._vendor.distlib.scripts import ScriptMaker
 from pip._vendor.packaging.utils import canonicalize_name
 from pip._vendor.six import StringIO
@@ -602,58 +600,6 @@ def supported(self, tags=None):
         return bool(set(tags).intersection(self.file_tags))
 
 
-class BuildEnvironment(object):
-    """Context manager to install build deps in a simple temporary environment
-    """
-    def __init__(self, no_clean):
-        self._temp_dir = TempDirectory(kind="build-env")
-        self._no_clean = no_clean
-
-    def __enter__(self):
-        self._temp_dir.create()
-
-        self.save_path = os.environ.get('PATH', None)
-        self.save_pythonpath = os.environ.get('PYTHONPATH', None)
-
-        install_scheme = 'nt' if (os.name == 'nt') else 'posix_prefix'
-        install_dirs = get_paths(install_scheme, vars={
-            'base': self._temp_dir.path,
-            'platbase': self._temp_dir.path,
-        })
-
-        scripts = install_dirs['scripts']
-        if self.save_path:
-            os.environ['PATH'] = scripts + os.pathsep + self.save_path
-        else:
-            os.environ['PATH'] = scripts + os.pathsep + os.defpath
-
-        if install_dirs['purelib'] == install_dirs['platlib']:
-            lib_dirs = install_dirs['purelib']
-        else:
-            lib_dirs = install_dirs['purelib'] + os.pathsep + \
-                install_dirs['platlib']
-        if self.save_pythonpath:
-            os.environ['PYTHONPATH'] = lib_dirs + os.pathsep + \
-                self.save_pythonpath
-        else:
-            os.environ['PYTHONPATH'] = lib_dirs
-
-        return self._temp_dir.path
-
-    def __exit__(self, exc_type, exc_val, exc_tb):
-        if not self._no_clean:
-            self._temp_dir.cleanup()
-        if self.save_path is None:
-            os.environ.pop('PATH', None)
-        else:
-            os.environ['PATH'] = self.save_path
-
-        if self.save_pythonpath is None:
-            os.environ.pop('PYTHONPATH', None)
-        else:
-            os.environ['PYTHONPATH'] = self.save_pythonpath
-
-
 class WheelBuilder(object):
     """Build wheels from a RequirementSet."""
 
@@ -667,65 +613,14 @@ def __init__(self, finder, preparer, wheel_cache,
 
         self.build_options = build_options or []
         self.global_options = global_options or []
-        self.no_clean = no_clean
-
-    def _find_build_reqs(self, req):
-        """Get a list of the packages required to build the project, if any,
-        and a flag indicating whether pyproject.toml is present, indicating
-        that the build should be isolated.
-
-        Build requirements can be specified in a pyproject.toml, as described
-        in PEP 518. If this file exists but doesn't specify build
-        requirements, pip will default to installing setuptools and wheel.
-        """
-        if os.path.isfile(req.pyproject_toml):
-            with open(req.pyproject_toml) as f:
-                pp_toml = pytoml.load(f)
-            return pp_toml.get('build-system', {})\
-                .get('requires', ['setuptools', 'wheel']), True
-
-        return ['setuptools', 'wheel'], False
-
-    def _install_build_reqs(self, reqs, prefix):
-        # Local import to avoid circular import (wheel <-> req_install)
-        from pip._internal.req.req_install import InstallRequirement
-        from pip._internal.index import FormatControl
-        # Ignore the --no-binary option when installing the build system, so
-        # we don't recurse trying to build a self-hosting build system.
-        finder = copy.copy(self.finder)
-        finder.format_control = FormatControl(set(), set())
-        urls = [finder.find_requirement(InstallRequirement.from_line(r),
-                                        upgrade=False).url
-                for r in reqs]
-
-        args = [sys.executable, '-m', 'pip', 'install', '--ignore-installed',
-                '--prefix', prefix] + list(urls)
-        with open_spinner("Installing build dependencies") as spinner:
-            call_subprocess(args, show_stdout=False, spinner=spinner)
 
     def _build_one(self, req, output_dir, python_tag=None):
         """Build one wheel.
 
         :return: The filename of the built wheel, or None if the build failed.
         """
-        build_reqs, isolate = self._find_build_reqs(req)
-        if 'setuptools' not in build_reqs:
-            logger.warning(
-                "This version of pip does not implement PEP 516, so "
-                "it cannot build a wheel without setuptools. You may need to "
-                "upgrade to a newer version of pip.")
-        # Install build deps into temporary directory (PEP 518)
-        with BuildEnvironment(self.no_clean) as prefix:
-            self._install_build_reqs(build_reqs, prefix)
-            return self._build_one_inside_env(req, output_dir,
-                                              python_tag=python_tag,
-                                              isolate=True)
-
-    def _build_one_inside_env(self, req, output_dir, python_tag=None,
-                              isolate=False):
         with TempDirectory(kind="wheel") as temp_dir:
-            if self.__build_one(req, temp_dir.path, python_tag=python_tag,
-                                isolate=isolate):
+            if self.__build_one(req, temp_dir.path, python_tag=python_tag):
                 try:
                     wheel_name = os.listdir(temp_dir.path)[0]
                     wheel_path = os.path.join(output_dir, wheel_name)
@@ -740,20 +635,14 @@ def _build_one_inside_env(self, req, output_dir, python_tag=None,
             self._clean_one(req)
             return None
 
-    def _base_setup_args(self, req, isolate=False):
-        flags = '-u'
-        # The -S flag currently breaks Python in virtualenvs, because it relies
-        # on site.py to find parts of the standard library outside the env. So
-        # isolation is disabled for now.
-        # if isolate:
-        #     flags += 'S'
+    def _base_setup_args(self, req):
         return [
-            sys.executable, flags, '-c',
+            sys.executable, '-u', '-c',
             SETUPTOOLS_SHIM % req.setup_py
         ] + list(self.global_options)
 
-    def __build_one(self, req, tempd, python_tag=None, isolate=False):
-        base_args = self._base_setup_args(req, isolate=isolate)
+    def __build_one(self, req, tempd, python_tag=None):
+        base_args = self._base_setup_args(req)
 
         spin_message = 'Running setup.py bdist_wheel for %s' % (req.name,)
         with open_spinner(spin_message) as spinner:
@@ -764,13 +653,8 @@ def __build_one(self, req, tempd, python_tag=None, isolate=False):
             if python_tag is not None:
                 wheel_args += ["--python-tag", python_tag]
 
-            env = {}
-            if isolate:
-                env['PYTHONNOUSERSITE'] = '1'
-
             try:
                 call_subprocess(wheel_args, cwd=req.setup_py_dir,
-                                extra_environ=env,
                                 show_stdout=False, spinner=spinner)
                 return True
             except: