bpo-36235: Fix CFLAGS in distutils customize_compiler() (GH-12236) (GH-12349)

Fix CFLAGS in customize_compiler() of distutils.sysconfig: when the
CFLAGS environment variable is defined, don't override CFLAGS variable with
the OPT variable anymore.

Initial patch written by David Malcolm.

Co-Authored-By: David Malcolm <dmalcolm@redhat.com>
(cherry picked from commit 86082c22d23285995a32aabb491527c9f5629556)

3 files changed, 33 insertions, 4 deletions

diff --git a/Lib/distutils/sysconfig.py b/Lib/distutils/sysconfig.py
index de7da1d413..8f49dac6b1 100644
--- a/Lib/distutils/sysconfig.py
+++ b/Lib/distutils/sysconfig.py
@@ -171,8 +171,8 @@ def customize_compiler(compiler):
                 _osx_support.customize_compiler(_config_vars)
                 _config_vars['CUSTOMIZED_OSX_COMPILER'] = 'True'
 
-        (cc, cxx, opt, cflags, ccshared, ldshared, so_ext, ar, ar_flags) = \
-            get_config_vars('CC', 'CXX', 'OPT', 'CFLAGS',
+        (cc, cxx, cflags, ccshared, ldshared, so_ext, ar, ar_flags) = \
+            get_config_vars('CC', 'CXX', 'CFLAGS',
                             'CCSHARED', 'LDSHARED', 'SO', 'AR',
                             'ARFLAGS')
 
@@ -196,7 +196,7 @@ def customize_compiler(compiler):
         if 'LDFLAGS' in os.environ:
             ldshared = ldshared + ' ' + os.environ['LDFLAGS']
         if 'CFLAGS' in os.environ:
-            cflags = opt + ' ' + os.environ['CFLAGS']
+            cflags = cflags + ' ' + os.environ['CFLAGS']
             ldshared = ldshared + ' ' + os.environ['CFLAGS']
         if 'CPPFLAGS' in os.environ:
             cpp = cpp + ' ' + os.environ['CPPFLAGS']
diff --git a/Lib/distutils/tests/test_sysconfig.py b/Lib/distutils/tests/test_sysconfig.py
index eb4d27c39e..2be5d245f9 100644
--- a/Lib/distutils/tests/test_sysconfig.py
+++ b/Lib/distutils/tests/test_sysconfig.py
@@ -8,8 +8,9 @@ import sys
 import textwrap
 
 from distutils import sysconfig
+from distutils.ccompiler import get_default_compiler
 from distutils.tests import support
-from test.test_support import TESTFN
+from test.test_support import TESTFN, swap_item
 
 class SysconfigTestCase(support.EnvironGuard,
                         unittest.TestCase):
@@ -50,6 +51,30 @@ class SysconfigTestCase(support.EnvironGuard,
         python_h = os.path.join(inc_dir, "Python.h")
         self.assertTrue(os.path.isfile(python_h), python_h)
 
+    @unittest.skipUnless(get_default_compiler() == 'unix',
+                         'not testing if default compiler is not unix')
+    def test_customize_compiler(self):
+        os.environ['AR'] = 'my_ar'
+        os.environ['CC'] = 'my_cc'
+        os.environ['ARFLAGS'] = '--myarflags'
+        os.environ['CFLAGS'] = '--mycflags'
+
+        # make sure AR gets caught
+        class compiler:
+            compiler_type = 'unix'
+
+            def set_executables(self, **kw):
+                self.exes = kw
+
+        # Make sure that sysconfig._config_vars is initialized
+        sysconfig.get_config_vars()
+
+        comp = compiler()
+        with swap_item(sysconfig._config_vars, 'CFLAGS', '--sysconfig-cflags'):
+            sysconfig.customize_compiler(comp)
+        self.assertEqual(comp.exes['archiver'], 'my_ar --myarflags')
+        self.assertEqual(comp.exes['compiler'], 'my_cc --sysconfig-cflags --mycflags')
+
     def test_parse_makefile_base(self):
         self.makefile = test.test_support.TESTFN
         fd = open(self.makefile, 'w')
diff --git a/Misc/NEWS.d/next/Library/2019-03-08-13-32-21.bpo-36235._M72wU.rst b/Misc/NEWS.d/next/Library/2019-03-08-13-32-21.bpo-36235._M72wU.rst
new file mode 100644
index 0000000000..59df98c101
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-03-08-13-32-21.bpo-36235._M72wU.rst
@@ -0,0 +1,4 @@
+Fix ``CFLAGS`` in ``customize_compiler()`` of ``distutils.sysconfig``: when
+the ``CFLAGS`` environment variable is defined, don't override ``CFLAGS``
+variable with the ``OPT`` variable anymore. Initial patch written by David
+Malcolm.