tk-update update

[Ludovic Courtès]

Hello!

As you may have noticed, the ‘tk-update’ branch is not merged yet.

There’s one problem, manifesting itself in webkitgtk-2.4
(http://hydra.gnu.org/build/831334):

--8<---------------cut here---------------start------------->8---
  GEN      DerivedSources/WebCore/CommandLineAPIModuleSource.h
Traceback (most recent call last):
  File 
"/gnu/store/7lqv9lk5j0kg6yrhwqh5cbwqbibzmxgl-glib-2.46.1-bin/bin/gdbus-codegen",
 line 37, in <module>
    from codegen import codegen_main
  File 
"/gnu/store/fvg98wicda2ia6wxx90gfbs8ydy27qdi-glib-2.46.1/share/glib-2.0/codegen/codegen_main.py",
 line 28, in <module>
    from . import parser
  File 
"/gnu/store/fvg98wicda2ia6wxx90gfbs8ydy27qdi-glib-2.46.1/share/glib-2.0/codegen/parser.py",
 line 23, in <module>
    import xml.parsers.expat
  File 
"/gnu/store/5v7xrwnzz0d1h9qfwwq5aaj33a6d7xm1-python-3.4.3/lib/python3.4/xml/parsers/expat.py",
 line 4, in <module>
    from pyexpat import *
ImportError: dynamic module does not define init function (PyInit_pyexpat)
--8<---------------cut here---------------end--------------->8---

The problem can be reproduced this way:

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix environment --ad-hoc python-2 python-3 -- python3
Python 3.4.3 (default, Jan  1 1970, 00:00:01) 
[GCC 4.9.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.environ['PYTHONPATH']
'/gnu/store/q405y94pbnx028mygranaww5pnbqhnq1-python-2.7.10/lib/python2.7/site-packages:/gnu/store/q405y94pbnx028mygranaww5pnbqhnq1-python-2.7.10/lib/python2.7/lib-dynload:/gnu/store/5v7xrwnzz0d1h9qfwwq5aaj33a6d7xm1-python-3.4.3/lib/python3.4/site-packages:/gnu/store/5v7xrwnzz0d1h9qfwwq5aaj33a6d7xm1-python-3.4.3/lib/python3.4/lib-dynload:/home/ludo/.guix-profile/lib/python2.7/site-packages:/run/current-system/profile/lib/python2.7/site-packages'
>>> import pyexpat
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: dynamic module does not define init function (PyInit_pyexpat)
--8<---------------cut here---------------end--------------->8---

What happens is that as a consequence of d7572b4, which does:

@@ -215,7 +233,8 @@
     (native-search-paths
      (list (search-path-specification
             (variable "PYTHONPATH")
-            (files '("lib/python2.7/site-packages")))))
+            (files '("lib/python2.7/site-packages"
+                     "lib/python2.7/lib-dynload")))))
     (home-page "http://python.org";)
     (synopsis "High-level, dynamically-typed programming language")
     (description

… we end up with python2’s pyexpat.so in the search path, and python3
fails when it tries to load it.  (This change was done so that .so files
such as tkinter.so can be found even when they don’t lie under Python’s
prefix.)

My analysis is that it’s “reasonable” to expect breakage when mixing
python2 and python3 in the same environment, and that the problem here
is more that standalone programs like ‘gdbus-codegen’ should be wrapped
to have their PYTHONPATH set in stone.

What do people think?

If there’s consensus, we need to fix GLib in that branch, which means
rebuilding a lot of things again (604 packages.)

Thanks,
Ludo’.