setuptools_scm hides errors from git in some cases

[brianmay]

I don't understand what is going on here - it seemed to work last time I tried this. Don't understand why it can't find the git command under tox either - git is installed:

$ tox -e py35        
GLOB sdist-make: /home/brian/tree/karaage/python-tldap/setup.py
py35 inst-nodeps: /home/brian/tree/karaage/python-tldap/.tox/dist/python-tldap-0.3.19.dev1+ng49acbbf.d20161201.zip
py35 installed: Django==1.10.3,ldap3==1.4.0,passlib==1.7.0,pyasn1==0.1.9,python-tldap==0.3.19.dev1+ng49acbbf.d20161201,setuptools-scm==1.15.0,six==1.10.0
py35 runtests: PYTHONHASHSEED='1976067474'
py35 runtests: commands[0] | ./setup.py test
/home/brian/tree/karaage/python-tldap/.tox/py35/lib/python3.5/site-packages/setuptools_scm/utils.py:108: UserWarning: 'git' was not found
  warnings.warn("%r was not found" % name)
Traceback (most recent call last):
  File "/home/brian/tree/karaage/python-tldap/setup.py", line 71, in <module>
    test_suite="tldap.tests",
  File "/home/brian/.pyenv/versions/3.5.1/lib/python3.5/distutils/core.py", line 108, in setup
    _setup_distribution = dist = klass(attrs)
  File "/home/brian/tree/karaage/python-tldap/.tox/py35/lib/python3.5/site-packages/setuptools/dist.py", line 318, in __init__
    _Distribution.__init__(self, attrs)
  File "/home/brian/.pyenv/versions/3.5.1/lib/python3.5/distutils/dist.py", line 281, in __init__
    self.finalize_options()
  File "/home/brian/tree/karaage/python-tldap/.tox/py35/lib/python3.5/site-packages/setuptools/dist.py", line 376, in finalize_options
    ep.load()(self, ep.name, value)
  File "/home/brian/tree/karaage/python-tldap/.tox/py35/lib/python3.5/site-packages/setuptools_scm/integration.py", line 19, in version_keyword
    dist.metadata.version = get_version(**value)
  File "/home/brian/tree/karaage/python-tldap/.tox/py35/lib/python3.5/site-packages/setuptools_scm/__init__.py", line 117, in get_version
    parsed_version = _do_parse(root, parse)
  File "/home/brian/tree/karaage/python-tldap/.tox/py35/lib/python3.5/site-packages/setuptools_scm/__init__.py", line 95, in _do_parse
    "use git+https://github.com/user/proj.git#egg=proj" % root)
LookupError: setuptools-scm was unable to detect version for '/home/brian/tree/karaage/python-tldap'.

Make sure you're either building from a fully intact git repository or PyPI tarballs. Most other sources (such as GitHub's tarballs, a git checkout without the .git folder) don't contain the necessary metadata and will not work.

For example, if you're using pip, instead of https://github.com/user/proj/archive/master.zip use git+https://github.com/user/proj.git#egg=proj
ERROR: InvocationError: '/home/brian/tree/karaage/python-tldap/setup.py test'
_________________________________________________________________ summary __________________________________________________________________
ERROR:   py35: commands failed

[brianmay]

Oh, looks like it is something weird to do with a python wrapper I have around git, simplified version that causes the failure:

#!/usr/bin/python
import os
import sys
import subprocess

home = os.environ['HOME']
os.execvp("/usr/bin/git", ["/usr/bin/git"] + sys.argv[1:])

If I delete the os.environ['HOME'] lookup it works. Weird. So starting to think this may not be setuptools_scm issue, unless it is doing something truly weird when searching for git.

[brianmay]

Oh, what I imagine is happening is the HOME environment variable isn't set, so this results in the process generating an exception - which setuptools_scm conveniently hides.

I am just going to assume that is the problem, and close this ticket.

[brianmay]

Having said that I really don't like it when applications silently hide errors like this; if git was broken, I want to know about it.

[RonnyPfannschmidt]

fixed as sidecar of #339