Provide SQL line table even if running coveragepy in branch coverage mode

[fkromer]

Is your feature request related to a problem? Please describe.

coveragepy provides the line table if run in line coverage mode and the arc table when run in branch coverage mode. python-tia depends on the line to context_id mapping in the line table and should be able to access this data even if coveragepy is run in branch coverage mode.

Describe the solution you'd like

Provide an option to enable line table generation in addition to arc table generation. This prevents from runtime overheads for users which don't need both tables and allows data availability for those which need it.

[nedbat]

Would a SQLite view work for you?

    create view line (file_id, context_id, lineno) as 
    select file_id, context_id, fromno from arc where fromno > 0 
    union
    select file_id, context_id, tono from arc where tono > 0;

[fkromer]

I'm using a simple wrapper for the SQL database access. A SQLite view is not suitable for me. This would require to run coveragepy twice to get both tables I guess. However I'd prefer to have either (1) the line info contained in the arc table as well or (2) the line table generated in addition to the arc table when coveragepy is run in branch coverage mode.

[nedbat]

I don't understand why you would need to run coverage twice. Maybe I didn't explain enough: my idea is that the schema depends on whether you are measuring branch coverage. If not, then you have a line table and no arc table. If you measure branch coverage, then you have an arc table and a line view. So either way you could select from line. It seems pointless to store the data twice, in both the arc table and the line table.

[fkromer]

Ah, I understand. Right, storing the data twice makes no sense. Should work for me. Btw: This request is not urgent because I need it for a spare time project only.

[Bachmann1234]

Howdy! I was poking around the pre release tag.

I thew this view into a branch https://github.com/Bachmann1234/coveragepy/tree/line_view and ran it against a project of mine

I was going to write some tests and spin up a PR but first I wanted to confirm this was the solution you wanted.

[nedbat]

I'm not sure what to do with this request. As of now, the line table is not a simple thing to work with. The line numbers are stored in a packed binary format, so we can't mimic it with a view based on the arc table any more.