Figure out workaround for too long shebang lines

[nailor]

Due to the shebang manipulation the shebang lines can grow a lot in size, depending on the project name and installation location.

Unfortunately shebang line usually limits to 127 characters and the only way to tweak it is to recompile the kernel. Proper workaround might be to ship a custom shebang runner with this

[guilhem]

@nailor We can use this http://virtualenv.readthedocs.org/en/latest/virtualenv.html#making-environments-relocatable

I using it to do same thing than dh-virtualenv but manually.
shebang become:

#!/usr/bin/env python2.7

import os; activate_this=os.path.join(os.path.dirname(os.path.realpath(__file__)), 'activate_this.py'); exec(compile(open(activate_this).read(), activate_this, 'exec'), dict(__file__=activate_this)); del os, activate_this

[jhermann]

This would also be an elegant solution for #48, btw. The "--system-site-packages" handling would have to be investigated, though – but for a debianzed virtualenv, having the system packages available is not the worst thing that can happen.

Also, referencing /usr/bin/python* directly might be the better choice, I don't really want an activated virtualenv in my home influence a package-installed app.

[nailor]

@guilhem: I'm not too big fan of the --relocatable flag. It is on the way out of virtualenv (well, has been like that for a loooooong time) plus there are some issues with it. Possibly the activate_this.py trick might work, but feels a bit ugly (limited to bin directory only, for example, though this is a thing that can be worked around). While the 127 can be kind annoying, don't really know how real problem this is. Anyway, definitely something we could experiment with!

@jhermann: Pointing to system python might be problematic regarding python paths etc. System packages should be available via a flag, but by default they can cause a lot of confusion.

[jhermann]

Including a modified version of https://github.com/jordansissel/shebang (that uses the shebang executable location to allow relative references to the wanted command) might help.

[nailor]

@jhermann That still has the problem of the line being longer than 127 characters, which is set in the kernel by BINPRM_BUF_SIZE.

[jhermann]

OK, slight variation then, install the launcher tool to e.g. /usr/bin/dh-venv-launch, and have it examine the script for its containing directory, then tack on the requested binary (i.e. "python") relative to that. That does require a sub-package of dh-virtualenv (e.g. dh-virtualenv-runtime or dh-virtualenv-support) that also gets deployed to the target machines once (created packages would Depend on that, and share it).

Bang paths would look like this (always):

    #!/usr/bin/dh-venv-launch python

POC:

    $ head -99 *.sh
    ==> launch.sh <==
    #!/bin/bash
    interpreter="$1"; shift
    script="$1"; shift
    exec $(dirname "$script")"/$interpreter" "$script" "$@"

    ==> test.sh <==
    #!launch.sh python
    print("Yay!")

    $ ./test.sh 
    Yay!

[nailor]

Closing this as not sure if fixing this after the upcoming default install path change makes any sense.