cli: read optional config from YAMLLINT_CONFIG

[jbergstroem]

This is a "minor" abi break (?) since empty configs are disregarded instead of failing.

Fixes: #107

[coveralls]

Coverage decreased (-0.1%) to 98.043% when pulling e52c1ac on jbergstroem:feature/environment-read into e4e99f0 on adrienverge:master.

[coveralls]

Coverage decreased (-0.1%) to 98.043% when pulling e52c1ac on jbergstroem:feature/environment-read into e4e99f0 on adrienverge:master.

[coveralls]

Coverage decreased (-0.1%) to 98.043% when pulling e52c1ac on jbergstroem:feature/environment-read into e4e99f0 on adrienverge:master.

[jbergstroem]

So, my minor logic change now left us with a few uncovered branches. Suggestions on how to tackle this? Add tests? Different route for handling the parsing of environment variables?

[jbergstroem]

@adrienverge any input on above?

[adrienverge]

Hi Johan, thanks, this looks good.

The API break is not problematic in my opinion, as empty config data resulted in an error.

Could you explain your comment on the few uncovered branches? I didn't get it.

About tests:

• test_run_with_empty_config() should be changed to run without error (on an existing file), as this is the new behaviour.
• Please add a case for checking that -d option overrides the environment.

[adrienverge]

Also, using -d '' should be a way to cancel the use of $YAMLLINT_CONFIG, what do you think? We would need a test for that.

[adrienverge]

@jbergstroem if you want to continue on this pull request, using YAMLLINT_CONFIG_DATA instead of YAMLLINT_CONFIG would be consistent with the new feature from #255 (review).