Create hooks and implement Debian's patches against those hooks. Fixes …

…#2.

distutils/command/install_egg_info.py

@@ -19,14 +19,17 @@ class install_egg_info(Command):
     def initialize_options(self):
         self.install_dir = None
 
-    def finalize_options(self):
-        self.set_undefined_options('install_lib',('install_dir','install_dir'))
-        basename = "%s-%s-py%d.%d.egg-info" % (
+    @property
+    def basename(self):
+        return "%s-%s-py%d.%d.egg-info" % (
             to_filename(safe_name(self.distribution.get_name())),
             to_filename(safe_version(self.distribution.get_version())),
             *sys.version_info[:2]
         )
-        self.target = os.path.join(self.install_dir, basename)
+
+    def finalize_options(self):
+        self.set_undefined_options('install_lib',('install_dir','install_dir'))
+        self.target = os.path.join(self.install_dir, self.basename)
         self.outputs = [self.target]
 
     def run(self):

distutils/debian.py

@@ -0,0 +1,117 @@
+"""
+Apply Debian-specific patches to distutils commands and sysconfig.
+
+Extracts the customized behavior from patches as reported
+in pypa/distutils#2 and applies those customizations (except
+for scheme definitions) to those commands.
+
+Call ``apply_customizations`` to have these customizations
+take effect. Debian can do that from site.py or similar::
+
+    with contextlib.suppress(ImportError):
+        import distutils.debian
+        distutils.debian.apply_customizations()
+"""
+
+import os
+import sys
+
+import distutils.sysconfig
+import distutils.command.install as orig_install
+import distutils.command.install_egg_info as orig_install_egg_info
+from distutils.command.install_egg_info import (
+    to_filename,
+    safe_name,
+    safe_version,
+    )
+from distutils.errors import DistutilsOptionError
+
+
+class install(orig_install.install):
+    user_options = list(orig_install.install.user_options) + [
+        ('install-layout=', None,
+         "installation layout to choose (known values: deb, unix)"),
+    ]
+
+    def initialize_options(self):
+        super().initialize_options()
+        self.prefix_option = None
+        self.install_layout = None
+
+    def finalize_unix(self):
+        self.prefix_option = self.prefix
+        super().finalize_unix()
+        if self.install_layout:
+            if self.install_layout.lower() in ['deb']:
+                self.select_scheme("deb_system")
+            elif self.install_layout.lower() in ['unix']:
+                self.select_scheme("unix_prefix")
+            else:
+                raise DistutilsOptionError(
+                    "unknown value for --install-layout")
+        elif ((self.prefix_option and
+               os.path.normpath(self.prefix) != '/usr/local')
+              or sys.base_prefix != sys.prefix
+              or 'PYTHONUSERBASE' in os.environ
+              or 'VIRTUAL_ENV' in os.environ
+              or 'real_prefix' in sys.__dict__):
+            self.select_scheme("unix_prefix")
+        else:
+            if os.path.normpath(self.prefix) == '/usr/local':
+                self.prefix = self.exec_prefix = '/usr'
+                self.install_base = self.install_platbase = '/usr'
+            self.select_scheme("unix_local")
+
+
+class install_egg_info(orig_install_egg_info.install_egg_info):
+    user_options = list(orig_install_egg_info.install_egg_info.user_options) + [
+        ('install-layout', None, "custom installation layout"),
+    ]
+
+    def finalize_options(self):
+        self.set_undefined_options('install',('install_layout','install_layout'))
+        self.set_undefined_options('install',('prefix_option','prefix_option'))
+
+    @property
+    def basename(self):
+        if self.install_layout:
+            if not self.install_layout.lower() in ['deb', 'unix']:
+                raise DistutilsOptionError(
+                    "unknown value for --install-layout")
+            no_pyver = (self.install_layout.lower() == 'deb')
+        elif self.prefix_option:
+            no_pyver = False
+        else:
+            no_pyver = True
+        if no_pyver:
+            basename = "%s-%s.egg-info" % (
+                to_filename(safe_name(self.distribution.get_name())),
+                to_filename(safe_version(self.distribution.get_version()))
+                )
+        else:
+            basename = "%s-%s-py%d.%d.egg-info" % (
+                to_filename(safe_name(self.distribution.get_name())),
+                to_filename(safe_version(self.distribution.get_version())),
+                *sys.version_info[:2]
+            )
+        return basename
+
+
+def _posix_lib(standard_lib, libpython, early_prefix, prefix):
+    is_default_prefix = not early_prefix or os.path.normpath(early_prefix) in ('/usr', '/usr/local')
+    if standard_lib:
+        return libpython
+    elif (is_default_prefix and
+              'PYTHONUSERBASE' not in os.environ and
+              'VIRTUAL_ENV' not in os.environ and
+              'real_prefix' not in sys.__dict__ and
+              sys.prefix == sys.base_prefix):
+            return os.path.join(prefix, "lib", "python3", "dist-packages")
+    else:
+        return os.path.join(libpython, "site-packages")
+
+
+def apply_customizations():
+    orig_install.install = install
+    orig_install_egg_info.install_egg_info = install_egg_info
+    distutils.sysconfig._posix_lib = _posix_lib

distutils/sysconfig.py

@@ -129,6 +129,13 @@ def get_python_inc(plat_specific=0, prefix=None):
             "on platform '%s'" % os.name)
 
 
+def _posix_lib(standard_lib, libpython, early_prefix, prefix):
+    if standard_lib:
+        return libpython
+    else:
+        return os.path.join(libpython, "site-packages")
+
+
 def get_python_lib(plat_specific=0, standard_lib=0, prefix=None):
     """Return the directory containing the Python library (standard or
     site additions).
@@ -152,6 +159,8 @@ def get_python_lib(plat_specific=0, standard_lib=0, prefix=None):
             return os.path.join(prefix, "lib-python", sys.version[0])
         return os.path.join(prefix, 'site-packages')
 
+    early_prefix = prefix
+
     if prefix is None:
         if standard_lib:
             prefix = plat_specific and BASE_EXEC_PREFIX or BASE_PREFIX
@@ -169,10 +178,7 @@ def get_python_lib(plat_specific=0, standard_lib=0, prefix=None):
         implementation = 'pypy' if IS_PYPY else 'python'
         libpython = os.path.join(prefix, libdir,
                                  implementation + get_python_version())
-        if standard_lib:
-            return libpython
-        else:
-            return os.path.join(libpython, "site-packages")
+        return _posix_lib(standard_lib, libpython, early_prefix, prefix)
     elif os.name == "nt":
         if standard_lib:
             return os.path.join(prefix, "Lib")