BLD: Use Azure pipelines for linting

At the moment we have the script ci/lint.sh for validating PEP-8 and other linting. The script has several validations in the form of:

   echo "Linting *.py"
    flake8 pandas --filename=*.py --exclude pandas/_libs/src --ignore=C406,C408,C409,E402,E731,E741,W503
    if [ $? -ne "0" ]; then
        RET=1
    fi

If I’m not wrong, moving all those to the azure-pipelines configuration would have two advantages.

First, the code would be simpler, as all the bash stuff would be automatically managed, and we’ld simply have:

  - script: flake8 pandas --filename=*.py --exclude pandas/_libs/src --ignore=C406,C408,C409,E402,E731,E741,W503
displayName: 'Linting *.py'

Second is that when one of those fails, it’ll be faster to see which is the reason for the fail in the azure pipeline dashboard, instead of having to go into the details of the travis log.

Does this make sense? @jreback @TomAugspurger @chrisrpatterson @jeremyepling

[datapythonista]

Made some progress on this, and managed to make flake8 generate the correct output:

https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=437&view=logs

It really improves the clarity of the errors (and even much more compared to our current solution, in the travis log). But still some issues:

• cpplint doesn’t seem to allow custom output (it has a --output parameter that can be emacs, vs7, eclipse… but not a custom one)
• The number of errors reported by azure is wrong. We’ve got like 50 errors in the first failing step if we enter the log, but in the preview there are 11, and it says we’ve got just 11. Weird
• The link is not created. I see there is a ##vso[task.setendpoint]value option in https://github.com/Microsoft/vsts-tasks/blob/master/docs/authoring/commands.md, but it’s unclear how this needs to be used.

We probably don’t want to change the flake8 format in setup.cfg (would change it when flake8 is run locally too). But in any case, doesn’t seem to work, as the %(path)s are rendered by ConfigParser, and it fails to install flake8 in azure.

[gfyoung]

it’ll be faster to see which is the reason for the fail in the azure pipeline dashboard, instead of having to go into the details of the travis log.

FYI @pandas-dev/pandas-core : the reason why we can’t view the pipeline dashboard for Travis is because we don’t have the Travis GitHub app enabled on this repository.

Unfortunately, there is no way to migrate from travis-ci.org to travis-ci.com at the moment, which is pre-requisite for using the GitHub app.