Fix test_distutils to not fail when running 'make test' from a Python build

directory that is not the source directory (ie, one created using
'/path/to/source/configure'.) Leaves this test very slightly degraded in
that particular case, compared to the build-in-sourcedir case, but that case
isn't a particularly strong test either: neither test the actual path that
will be used after installing. There isn't a particularly good way to test
this, and a poor test beats a failing test.

Lib/distutils/tests/test_sysconfig.py

@@ -19,7 +19,27 @@ class SysconfigTestCase(unittest.TestCase):
         # test for pythonxx.lib?
 
     def test_get_python_inc(self):
+        # The check for srcdir is copied from Python's setup.py,
+        # and is necessary to make this test pass when building
+        # Python in a directory other than the source directory.
+        (srcdir,) = sysconfig.get_config_vars('srcdir')
+        if not srcdir:
             inc_dir = sysconfig.get_python_inc()
+        else:
+            # This test is not really a proper test: when building
+            # Python from source, even in the same directory,
+            # we won't be testing the same thing as when running
+            # distutils' tests on an installed Python. Nevertheless,
+            # let's try to do our best: if we are running Python's
+            # unittests from a build directory that is not the source
+            # directory, the normal inc_dir will exist, it will just not
+            # contain anything of interest.
+            inc_dir = sysconfig.get_python_inc()
+            self.assert_(os.path.isdir(inc_dir))
+            # Now test the source location, to make sure Python.h does
+            # exist.
+            inc_dir = os.path.join(os.getcwd(), srcdir, 'Include')
+            inc_dir = os.path.normpath(inc_dir)
         self.assert_(os.path.isdir(inc_dir), inc_dir)
         python_h = os.path.join(inc_dir, "Python.h")
         self.assert_(os.path.isfile(python_h), python_h)

setup.py

@@ -119,6 +119,8 @@ class PyBuildExt(build_ext):
             raise ValueError("No source directory; cannot proceed.")
 
         # Figure out the location of the source code for extension modules
+        # (This logic is copied in distutils.test.test_sysconfig,
+        # so building in a separate directory does not break test_distutils.)
         moddir = os.path.join(os.getcwd(), srcdir, 'Modules')
         moddir = os.path.normpath(moddir)
         srcdir, tail = os.path.split(moddir)