$TEXINPUTS provided from outside are dropped

[Natureshadow]

When specifying TEXINPUTS in the environment when calling sdaps (as done in the new Debian package to run the test suite without the package being installed, and after applying a patch that stops copying the classes to the project directory - see #27), they are dropped once something starts specifying its own TEXINPUTS inside the code.

It should instead be merged (PR follows).

[benzea]

I pushed a similar solution filtering possible duplicate entries for local directory and default search paths.

[davidmehren]

This commit broke the tests (and actually creating any new projects) for me.
In

sdaps/sdaps/utils/latex.py

Line 179 in a380a88

def compile(texfile, cwd, inputs=None):

input gets set to None and is then passed to run_engine which tries to execute extend() on it:

sdaps/sdaps/utils/latex.py

Line 163 in a380a88

inputs.extend(p for p in os.environ.get('TEXINPUTS', '').split(':') if p not in ['.', ''])

This fails and therefore breaks any LaTeX compilation with a error like

Error: An error occured in the setup routine. The survey directory still exists. You can for example check the questionnaire.log file for LaTeX compile errors.
Traceback (most recent call last):
  File "/home/david/Projekte/aur/sdaps-git/src/sdaps/sdaps/__init__.py", line 65, in main
    return cmdline['_func'](cmdline)
  File "/home/david/Projekte/aur/sdaps-git/src/sdaps/sdaps/cmdline/setup.py", line 45, in setup
    return setuptex.setup(cmdline['project'], cmdline['questionnaire.tex'], cmdline['additional_questions'], cmdline['add'])
  File "/home/david/Projekte/aur/sdaps-git/src/sdaps/sdaps/setuptex/__init__.py", line 104, in setup
    latex.compile('questionnaire.tex', cwd=survey.path())
  File "/home/david/Projekte/aur/sdaps-git/src/sdaps/sdaps/utils/latex.py", line 180, in compile
    run_engine(texfile, cwd, inputs)
  File "/home/david/Projekte/aur/sdaps-git/src/sdaps/sdaps/utils/latex.py", line 176, in run_engine
    preexec_fn=_preexec_fn)
  File "/usr/lib/python3.6/subprocess.py", line 267, in call
    with Popen(*popenargs, **kwargs) as p:
  File "/usr/lib/python3.6/subprocess.py", line 709, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.6/subprocess.py", line 1345, in _execute_child
    raise child_exception_type(err_msg)
subprocess.SubprocessError: Exception occurred in preexec_fn.

Just setting the default value of inputs to [] instead of None in compile should fix that, I think.

[benzea]

Oh, of course, I missed that follow up change and didn't run the tests!

I pushed the fix, thanks!