Rename _distutils_importer to _distutils_hack, as it supplies more than just an importer.

3 files changed, 104 insertions, 0 deletions

diff --git a/_distutils_hack/__init__.py b/_distutils_hack/__init__.py
new file mode 100644
index 00000000..3ad70100
--- /dev/null
+++ b/_distutils_hack/__init__.py
@@ -0,0 +1,45 @@
+import sys
+import os
+
+
+def enabled():
+    """
+    Allow selection of distutils by environment variable.
+    """
+    which = os.environ.get('SETUPTOOLS_USE_DISTUTILS', 'stdlib')
+    return which == 'local'
+
+
+class DistutilsMetaFinder:
+    def find_spec(self, fullname, path, target=None):
+        if path is not None or fullname != "distutils":
+            return None
+
+        return self.get_distutils_spec()
+
+    def get_distutils_spec(self):
+        import importlib.util
+
+        class DistutilsLoader(importlib.util.abc.Loader):
+
+            def create_module(self, spec):
+                return importlib.import_module('._distutils', 'setuptools')
+
+            def exec_module(self, module):
+                pass
+
+        return importlib.util.spec_from_loader('distutils', DistutilsLoader())
+
+
+DISTUTILS_FINDER = DistutilsMetaFinder()
+
+
+def add_shim():
+    sys.meta_path.insert(0, DISTUTILS_FINDER)
+
+
+def remove_shim():
+    try:
+        sys.path.remove(DISTUTILS_FINDER)
+    except ValueError:
+        pass
diff --git a/_distutils_hack/install.py b/_distutils_hack/install.py
new file mode 100644
index 00000000..73f13b29
--- /dev/null
+++ b/_distutils_hack/install.py
@@ -0,0 +1,5 @@
+from . import enabled, add_shim
+
+
+if enabled():
+    add_shim()
diff --git a/_distutils_hack/override.py b/_distutils_hack/override.py
new file mode 100644
index 00000000..523139bb
--- /dev/null
+++ b/_distutils_hack/override.py
@@ -0,0 +1,54 @@
+"""
+Ensure that the local copy of distutils is preferred over stdlib.
+
+See https://github.com/pypa/setuptools/issues/417#issuecomment-392298401
+for more motivation.
+"""
+
+import sys
+import re
+import importlib
+import warnings
+
+from . import enabled
+
+
+is_pypy = '__pypy__' in sys.builtin_module_names
+
+
+def warn_distutils_present():
+    if 'distutils' not in sys.modules:
+        return
+    if is_pypy and sys.version_info < (3, 7):
+        # PyPy for 3.6 unconditionally imports distutils, so bypass the warning
+        # https://foss.heptapod.net/pypy/pypy/-/blob/be829135bc0d758997b3566062999ee8b23872b4/lib-python/3/site.py#L250
+        return
+    warnings.warn(
+        "Distutils was imported before Setuptools. This usage is discouraged "
+        "and may exhibit undesirable behaviors or errors. Please use "
+        "Setuptools' objects directly or at least import Setuptools first.")
+
+
+def clear_distutils():
+    if 'distutils' not in sys.modules:
+        return
+    warnings.warn("Setuptools is replacing distutils.")
+    mods = [name for name in sys.modules if re.match(r'distutils\b', name)]
+    for name in mods:
+        del sys.modules[name]
+
+
+def ensure_local_distutils():
+    clear_distutils()
+    distutils = importlib.import_module('setuptools._distutils')
+    distutils.__name__ = 'distutils'
+    sys.modules['distutils'] = distutils
+
+    # sanity check that submodules load as expected
+    core = importlib.import_module('distutils.core')
+    assert '_distutils' in core.__file__, core.__file__
+
+
+warn_distutils_present()
+if enabled():
+    ensure_local_distutils()