MAINT: add warning to numpy.distutils for LDFLAGS append behavior.

See gh-7427

1 files changed, 13 insertions, 2 deletions

diff --git a/numpy/distutils/fcompiler/environment.py b/numpy/distutils/fcompiler/environment.py
index 489784580..4238f35cb 100644
--- a/numpy/distutils/fcompiler/environment.py
+++ b/numpy/distutils/fcompiler/environment.py
@@ -1,6 +1,7 @@
 from __future__ import division, absolute_import, print_function
 
 import os
+import warnings
 from distutils.dist import Distribution
 
 __metaclass__ = type
@@ -54,8 +55,18 @@ class EnvironmentConfig(object):
         if envvar is not None:
             envvar_contents = os.environ.get(envvar)
             if envvar_contents is not None:
-                if var and append and os.environ.get('NPY_DISTUTILS_APPEND_FLAGS', '0') == '1':
-                    var = var + [envvar_contents]
+                if var and append:
+                    if os.environ.get('NPY_DISTUTILS_APPEND_FLAGS', '0') == '1':
+                        var = var + [envvar_contents]
+                    else:
+                        var = envvar_contents
+                        if 'NPY_DISTUTILS_APPEND_FLAGS' not in os.environ.keys():
+                            msg = "{} is used as is, not appended ".format(envvar) + \
+                                  "to flags already defined " + \
+                                  "by numpy.distutils! Use NPY_DISTUTILS_APPEND_FLAGS=1 " + \
+                                  "to obtain appending behavior instead (this " + \
+                                  "behavior will become default in a future release)."
+                            warnings.warn(msg, UserWarning, stacklevel=3)
                 else:
                     var = envvar_contents
         if confvar is not None and self._conf: