Take advantage of .coverage being a SQLite database

[simonw]

The .coverage file generated by running pytest-cov is now a SQLite database!

I could do something interesting with this. Maybe after each test run for a new commit I could store that database file somewhere?

Lots of interesting challenges here.

I got a change into coveragepy last year which helps make the custom SQL functions available for doing fun things in Datasette: nedbat/coveragepy#868

Bigger challenge: if I have a DB file for every commit, that's hundreds (potentially thousands) of DB files. Datasette isn't designed to handle thousands of files like that.

So, do I figure out how to have Datasette open a file on-command for just a single request? Or, an easier option, do I copy data from those files into a single database with a modified schema to include the commit hash in each table row?

(Following on from #841 and #844)

[simonw]

Filed a related issue with some ideas against coveragepy here: nedbat/coveragepy#999

[simonw]

On closer inspection, I don't know if there's that much useful stuff you can do with the data from .coverage on its own.

Consider the following query against a .coverage run against Datasette itself:

select file_id, context_id, numbits_to_nums(numbits) from line_bits

It looks like this tells me which lines of which files were executed during the test run. But... without the actual source code, I don't think I can calculate the coverage percentage for each file. I don't want to count comment lines or whitespace as untested for example, and I don't know how many lines were in the file.

If I'm right that it's not possible to calculate percentage coverage from just the .coverage data then I'll need to do something a bit more involved - maybe parsing the coverage.xml report and loading that into my own schema?

[simonw]

Here's the plugin that adds those custom SQLite functions:

from datasette import hookimpl
from coverage.numbits import register_sqlite_functions


@hookimpl
def prepare_connection(conn):
    register_sqlite_functions(conn)

[simonw]

I'm happy enough with https://codecov.io/gh/simonw/datasette that I'm not going to spend any more time on this.