pkg/52755: lang/python27 needs comp.tgz to find shared libraries

[Pierre Pronchery <khorben%defora.org@localhost>]

>Number:         52755
>Category:       pkg
>Synopsis:       ctypes.util.find_library() fails without the "comp" set
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Nov 22 23:55:00 +0000 2017
>Originator:     Pierre Pronchery <khorben%defora.org@localhost>
>Release:        NetBSD 7.1_STABLE
>Organization:
>Environment:
System: NetBSD hostname 7.1_STABLE NetBSD 7.1_STABLE (CGDROOT_XEN3_DOM0) amd64
Architecture: x86_64
Machine: amd64
>Description:
Many Python-based programs and packages will fail to work without the "comp"
set installed, since ctypes.util.find_library() will not find any library
without it being installed.

This is notably the case with sysutils/salt:

hostname# salt-key -F
Traceback (most recent call last):
  File "/usr/pkg/bin/salt-key", line 10, in <module>
    salt_key()
  File "/usr/pkg/lib/python2.7/site-packages/salt/scripts.py", line 361, in salt
_key
[...]
  File "/usr/pkg/lib/python2.7/site-packages/salt/utils/rsax931.py", line 49, in
 _load_libcrypto
    raise OSError('Cannot locate OpenSSL libcrypto')
OSError: Cannot locate OpenSSL libcrypto

The documentation for Python's ctypes says:

> On Linux, find_library tries to run external programs (/sbin/ldconfig, gcc,
> and objdump) to find the library file. It returns the filename of the library
> file. Here are sone examples: 

So I suppose on NetBSD it relies on gcc and objdump.

>How-To-Repeat:

hostname# ls /etc/mtree/set.comp
ls: /etc/mtree/set.comp: No such file or directory
hostname# python2.7 
Python 2.7.14 (default, Oct 24 2017, 00:11:35) 
[GCC 4.8.5] on netbsd7
Type "help", "copyright", "credits" or "license" for more information.
>>> import ctypes.util
>>> print ctypes.util.find_library("crypto")
None
>>> ^D
hostname# progress -f comp.tgz tar xzpf -        
100% |***********************************|   104 MiB   11.44 MiB/s    00:00 ETA
hostname# python2.7 
>>> import ctypes.util
>>> print ctypes.util.find_library("crypto")
libcrypto.so.8

>Fix:
To work around the problem, install the "comp" set. However I do not
think we can expect users to have to install it. I avoid installing it
as often as possible myself (notably for security reasons).

I am not sure what the proper fix should be:
- let lang/python* depend on an implementation of lang/gcc
- adding a message when installing lang/python*

I would clearly prefer the former.