Fix missing imports in setup scripts generated by packaging (#13205).

I’ve made more edits than the bug report suggested to make sure the
generated setup script is compatible with many Python versions; a
comment in the source explains that in detail.

The cfg_to_args function uses old 2.x idioms like codecs.open and
RawConfigParser.readfp because I want the setup.py generated by packaging and
distutils2 to be the same.  Most users won’t see the deprecation warning and I
ignore it in the test suite.

Thanks to David Barnett for the report and original patch.

Lib/packaging/util.py

@@ -6,6 +6,7 @@ import csv
 import imp
 import sys
 import errno
+import codecs
 import shutil
 import string
 import hashlib
@@ -417,7 +418,8 @@ byte_compile(files, optimize=%r, force=%r,
             #   cfile - byte-compiled file
             #   dfile - purported source filename (same as 'file' by default)
             if optimize >= 0:
-                cfile = imp.cache_from_source(file, debug_override=not optimize)
+                cfile = imp.cache_from_source(file,
+                                              debug_override=not optimize)
             else:
                 cfile = imp.cache_from_source(file)
             dfile = file
@@ -931,6 +933,24 @@ def _iglob(path_glob):
                     yield file
 
 
+# HOWTO change cfg_to_args
+#
+# This function has two major constraints: It is copied by inspect.getsource
+# in generate_setup_py; it is used in generated setup.py which may be run by
+# any Python version supported by distutils2 (2.4-3.3).
+#
+# * Keep objects like D1_D2_SETUP_ARGS static, i.e. in the function body
+#   instead of global.
+# * If you use a function from another module, update the imports in
+#   SETUP_TEMPLATE.  Use only modules, classes and functions compatible with
+#   all versions: codecs.open instead of open, RawConfigParser.readfp instead
+#   of read, standard exceptions instead of Packaging*Error, etc.
+# * If you use a function from this module, update the template and
+#   generate_setup_py.
+#
+# test_util tests this function and the generated setup.py, but does not test
+# that it's compatible with all Python versions.
+
 def cfg_to_args(path='setup.cfg'):
     """Compatibility helper to use setup.cfg in setup.py.
 
@@ -941,8 +961,6 @@ def cfg_to_args(path='setup.cfg'):
     *file* is the path to the setup.cfg file.  If it doesn't exist,
     PackagingFileError is raised.
     """
-    # We need to declare the following constants here so that it's easier to
-    # generate the setup.py afterwards, using inspect.getsource.
 
     # XXX ** == needs testing
     D1_D2_SETUP_ARGS = {"name": ("metadata",),
@@ -986,10 +1004,11 @@ def cfg_to_args(path='setup.cfg'):
 
     # The real code starts here
     config = RawConfigParser()
-    if not os.path.exists(path):
-        raise PackagingFileError("file '%s' does not exist" %
-                                 os.path.abspath(path))
-    config.read(path, encoding='utf-8')
+    f = codecs.open(path, encoding='utf-8')
+    try:
+        config.readfp(f)
+    finally:
+        f.close()
 
     kwargs = {}
     for arg in D1_D2_SETUP_ARGS:
@@ -1011,8 +1030,11 @@ def cfg_to_args(path='setup.cfg'):
                     filenames = split_multiline(filenames)
                     in_cfg_value = []
                     for filename in filenames:
-                        with open(filename) as fp:
+                        fp = codecs.open(filename, encoding='utf-8')
+                        try:
                             in_cfg_value.append(fp.read())
+                        finally:
+                            fp.close()
                     in_cfg_value = '\n\n'.join(in_cfg_value)
             else:
                 continue
@@ -1029,13 +1051,19 @@ def cfg_to_args(path='setup.cfg'):
     return kwargs
 
 
-_SETUP_TMPL = """\
+SETUP_TEMPLATE = """\
 # This script was automatically generated by packaging
 import os
+import codecs
 from distutils.core import setup
-from ConfigParser import RawConfigParser
+try:
+    from ConfigParser import RawConfigParser
+except ImportError:
+    from configparser import RawConfigParser
 
-%(func)s
+%(split_multiline)s
+
+%(cfg_to_args)s
 
 setup(**cfg_to_args())
 """
@@ -1049,8 +1077,10 @@ def generate_setup_py():
     if os.path.exists("setup.py"):
         raise PackagingFileError("a setup.py file already exists")
 
+    source = SETUP_TEMPLATE % {'split_multiline': getsource(split_multiline),
+                               'cfg_to_args': getsource(cfg_to_args)}
     with open("setup.py", "w", encoding='utf-8') as fp:
-        fp.write(_SETUP_TMPL % {'func': getsource(cfg_to_args)})
+        fp.write(source)
 
 
 # Taken from the pip project
@@ -1307,6 +1337,8 @@ def get_install_method(path):
 def copy_tree(src, dst, preserve_mode=True, preserve_times=True,
               preserve_symlinks=False, update=False, verbose=True,
               dry_run=False):
+    # FIXME use of this function is why we get spurious logging message on
+    # stdout when tests run; kill and replace by shuil!
     from distutils.file_util import copy_file
 
     if not dry_run and not os.path.isdir(src):