Refactor the copying of xxmodule.c in distutils tests (#12141).

I need to copy this file in another test too, so I moved the support
code to distutils.tests.support and improved it:

- don’t skip when run from the Lib/distutils/tests directory
- use proper skip machinery instead of custom print/return/test suite
  fiddling.

tests/support.py

@@ -2,12 +2,15 @@
 import os
 import shutil
 import tempfile
+import unittest
+import sysconfig
 from copy import deepcopy
 
 from distutils import log
 from distutils.log import DEBUG, INFO, WARN, ERROR, FATAL
 from distutils.core import Distribution
 
+
 class LoggingSilencer(object):
 
     def setUp(self):
@@ -41,6 +44,7 @@ class LoggingSilencer(object):
     def clear_logs(self):
         self.logs = []
 
+
 class TempdirManager(object):
     """Mix-in class that handles temporary directories for test cases.
 
@@ -97,6 +101,7 @@ class TempdirManager(object):
 
         return pkg_dir, dist
 
+
 class DummyCommand:
     """Class to store options for retrieval via set_undefined_options()."""
 
@@ -107,6 +112,7 @@ class DummyCommand:
     def ensure_finalized(self):
         pass
 
+
 class EnvironGuard(object):
 
     def setUp(self):
@@ -123,3 +129,39 @@ class EnvironGuard(object):
                 del os.environ[key]
 
         super(EnvironGuard, self).tearDown()
+
+
+def copy_xxmodule_c(directory):
+    """Helper for tests that need the xxmodule.c source file.
+
+    Example use:
+
+            def test_compile(self):
+                copy_xxmodule_c(self.tmpdir)
+                self.assertIn('xxmodule.c', os.listdir(self.tmpdir)
+
+    If the source file can be found, it will be copied to *directory*.  If not,
+    the test will be skipped.  Errors during copy are not caught.
+    """
+    filename = _get_xxmodule_path()
+    if filename is None:
+        raise unittest.SkipTest('cannot find xxmodule.c (test must run in '
+                                'the python build dir)')
+    shutil.copy(filename, directory)
+
+
+def _get_xxmodule_path():
+    srcdir = sysconfig.get_config_var('srcdir')
+    candidates = [
+        # use installed copy if available
+        os.path.join(os.path.dirname(__file__), 'xxmodule.c'),
+        # otherwise try using copy from build directory
+        os.path.join(srcdir, 'Modules', 'xxmodule.c'),
+        # srcdir mysteriously can be $srcdir/Lib/distutils/tests when
+        # this file is run from its parent directory, so walk up the
+        # tree to find the real srcdir
+        os.path.join(srcdir, '..', '..', '..', 'Modules', 'xxmodule.c'),
+    ]
+    for path in candidates:
+        if os.path.exists(path):
+            return path

tests/test_build_ext.py

 import sys
 import os
-import shutil
 from io import StringIO
 import textwrap
 
 from distutils.core import Distribution
 from distutils.command.build_ext import build_ext
 from distutils import sysconfig
-from distutils.tests.support import TempdirManager
-from distutils.tests.support import LoggingSilencer
+from distutils.tests.support import (TempdirManager, LoggingSilencer,
+                                     copy_xxmodule_c)
 from distutils.extension import Extension
 from distutils.errors import (
     CompileError, DistutilsPlatformError, DistutilsSetupError,
@@ -16,20 +15,11 @@ from distutils.errors import (
 
 import unittest
 from test import support
-from test.support import run_unittest
 
 # http://bugs.python.org/issue4373
 # Don't load the xx module more than once.
 ALREADY_TESTED = False
 
-def _get_source_filename():
-    # use installed copy if available
-    tests_f = os.path.join(os.path.dirname(__file__), 'xxmodule.c')
-    if os.path.exists(tests_f):
-        return tests_f
-    # otherwise try using copy from build directory
-    srcdir = sysconfig.get_config_var('srcdir')
-    return os.path.join(srcdir, 'Modules', 'xxmodule.c')
 
 class BuildExtTestCase(TempdirManager,
                        LoggingSilencer,
@@ -41,9 +31,6 @@ class BuildExtTestCase(TempdirManager,
         self.tmp_dir = self.mkdtemp()
         self.sys_path = sys.path, sys.path[:]
         sys.path.append(self.tmp_dir)
-        filename = _get_source_filename()
-        if os.path.exists(filename):
-            shutil.copy(filename, self.tmp_dir)
         if sys.version > "2.6":
             import site
             self.old_user_base = site.USER_BASE
@@ -72,9 +59,8 @@ class BuildExtTestCase(TempdirManager,
 
     def test_build_ext(self):
         global ALREADY_TESTED
+        copy_xxmodule_c(self.tmp_dir)
         xx_c = os.path.join(self.tmp_dir, 'xxmodule.c')
-        if not os.path.exists(xx_c):
-            return
         xx_ext = Extension('xx', [xx_c])
         dist = Distribution({'name': 'xx', 'ext_modules': [xx_ext]})
         dist.package_dir = self.tmp_dir
@@ -518,13 +504,7 @@ class BuildExtTestCase(TempdirManager,
 
 
 def test_suite():
-    src = _get_source_filename()
-    if not os.path.exists(src):
-        if support.verbose:
-            print('test_build_ext: Cannot find source code (test'
-                  ' must run in python build dir)')
-        return unittest.TestSuite()
-    else: return unittest.makeSuite(BuildExtTestCase)
+    return unittest.makeSuite(BuildExtTestCase)
 
 if __name__ == '__main__':
     support.run_unittest(test_suite())