Fix distutils tests on Windows (#12678).

- First, support.fixup_build_ext (already used to set proper
  library_dirs value under Unix shared builds) gains the ability to
  correctly set the debug attribute under Windows debug builds.

- Second, the filename for the extension module gets a _d suffix under
  debug builds.

- Third, the test code properly puts our customized build_ext object
  into an internal dictionary to make sure that the install command will
  later use our object instead of re-creating one.  That’s the downside
  of using low-level APIs in our test code: we have to manually push
  knobs and turn handles that would otherwise be handled behind the
  scenes.

Thanks to Nadeem for the testing.

1 files changed, 17 insertions, 11 deletions

diff --git a/Lib/distutils/tests/support.py b/Lib/distutils/tests/support.py
index ffef98b..dc0e660 100644
--- a/Lib/distutils/tests/support.py
+++ b/Lib/distutils/tests/support.py
@@ -169,23 +169,29 @@ def _get_xxmodule_path():
 
 
 def fixup_build_ext(cmd):
-    """Function needed to make build_ext tests pass on shared builds.
+    """Function needed to make build_ext tests pass.
 
-    When Python was build with --enable-shared, -L. is not good enough to find
-    the libpython<blah>.so.  This is because regrtest runs it under a tempdir,
-    not in the top level where the .so lives.  By the time we've gotten here,
-    Python's already been chdir'd to the tempdir.  This function work arounds
-    that.  Example use:
+    When Python was build with --enable-shared on Unix, -L. is not good
+    enough to find the libpython<blah>.so.  This is because regrtest runs
+    it under a tempdir, not in the top level where the .so lives.  By the
+    time we've gotten here, Python's already been chdir'd to the tempdir.
+
+    When Python was built with in debug mode on Windows, build_ext commands
+    need their debug attribute set, and it is not done automatically for
+    some reason.
+
+    This function handles both of these things.  Example use:
 
         cmd = build_ext(dist)
         support.fixup_build_ext(cmd)
         cmd.ensure_finalized()
     """
-    # To further add to the fun, we can't just add library_dirs to the
-    # Extension() instance because that doesn't get plumbed through to the
-    # final compiler command.
-    if (sysconfig.get_config_var('Py_ENABLE_SHARED') and
-        not sys.platform.startswith('win')):
+    if os.name == 'nt':
+        cmd.debug = sys.executable.endswith('_d.exe')
+    elif sysconfig.get_config_var('Py_ENABLE_SHARED'):
+        # To further add to the shared builds fun on Unix, we can't just add
+        # library_dirs to the Extension() instance because that doesn't get
+        # plumbed through to the final compiler command.
         runshared = sysconfig.get_config_var('RUNSHARED')
         if runshared is None:
             cmd.library_dirs = ['.']