fortran extensions on OSX, issue with defining LDFLAGS

I ran into a problem while trying to build a conda package (https://github.com/praxes/hedm-conda-recipes/tree/master/imaged11) for a project with fortran extensions. python setup.py build works fine, but if`conda build`` simply invokes that same command, I get a string of errors about f2py not finding python symbols:

[...]
compiling Fortran sources
Fortran f77 compiler: /Users/darren/.conda/envs/_build/bin/gfortran -Wall -g -ffixed-form -fno-second-underscore -arch x86_64 -fPIC -O3 -funroll-loops
Fortran f90 compiler: /Users/darren/.conda/envs/_build/bin/gfortran -fopenmp -O2 -arch x86_64 -fPIC -O3 -funroll-loops
Fortran fix compiler: /Users/darren/.conda/envs/_build/bin/gfortran -Wall -g -ffixed-form -fno-second-underscore -fopenmp -O2 -arch x86_64 -fPIC -O3 -funroll-loops
creating build/temp.macosx-10.5-x86_64-2.7/fsrc
compile options: '-Ibuild/src.macosx-10.5-x86_64-2.7 -I/Users/darren/.conda/envs/_build/lib/python2.7/site-packages/numpy/core/include -I/Users/darren/.conda/envs/_build/include/python2.7 -c'
gfortran:f90: fsrc/fImageD11.f90
/Users/darren/.conda/envs/_build/bin/gfortran -Wall -g -Wl,-rpath,/Users/darren/.conda/envs/_build/lib -arch x86_64 build/temp.macosx-10.5-x86_64-2.7/build/src.macosx-10.5-x86_64-2.7/fImageD11module.o build/temp.macosx-10.5-x86_64-2.7/build/src.macosx-10.5-x86_64-2.7/fortranobject.o build/temp.macosx-10.5-x86_64-2.7/fsrc/fImageD11.o -L/Users/darren/.conda/envs/_build/lib/gcc/x86_64-apple-darwin11.4.2/4.8.5 -L/Users/darren/.conda/envs/_build/lib -lgomp -lpthread -lgfortran -o build/lib.macosx-10.5-x86_64-2.7/ImageD11/fImageD11.so
Undefined symbols for architecture x86_64:
  "_PyArg_ParseTupleAndKeywords", referenced from:
      _f2py_rout_fImageD11_compute_xlylzl in fImageD11module.o
      _f2py_rout_fImageD11_assign in fImageD11module.o
      _f2py_rout_fImageD11_compute_gv in fImageD11module.o
  "_PyCObject_AsVoidPtr", referenced from:
      _initfImageD11 in fImageD11module.o
      _F2PyCapsule_AsVoidPtr in fortranobject.o
  "_PyCObject_FromVoidPtr", referenced from:
      _fortran_getattr in fortranobject.o
      _F2PyCapsule_FromVoidPtr in fortranobject.o
[...]

What I found was that conda build defines LDFLAGS= -Wl,-rpath,/Users/darren/.conda/envs/_build/lib -arch x86_64, and if I unset LDFLAGS in my conda recipe’s build script, the package will compile. I asked about it on the conda mailing list, and someone replied that it appears f2py does not extend user-defined LDFLAGS, but instead let’s user-defined LDFLAGS overwrite its own (https://lists.macosforge.org/pipermail/macports-users/2010-November/022574.html), which on osx include “-undefined dynamic_lookup -bundle”. As it stands, it appears that anyone who needs to build a conda package on osx that includes fortran extensions will have to add the following to their build scripts:

LDFLAGS="$LDFLAGS -undefined dynamic_lookup -bundle"

Could f2py or numpy distutils extend user’s LDFLAGS with these required settings?

[isuruf]

Question: is it just annoying, or does it actually prevent some things you want to do?

At conda-forge, we set some LDFLAGS for external libraries to be found (-L$PREFIX/lib) and flags like -headerpad_max_install_names. This is done for all packages using compilers, not just python packages. Flags in LDFLAGS env var is meant to be appended in every other build system including python’s distutils, so that’s why conda-forge sets it.

[charris]

Done in #12551 I think.