[good-first-issue] Incomplete Cobertura XML spec support

[webknjaz]

Bug Report

The cobetura.xml file generated does not contain the lines-covered and lines-valid attributes. According to https://stackoverflow.com/a/71116722/595220, the spec is at https://github.com/cobertura/web/blob/master/htdocs/xml/coverage-04.dtd which has

<!ATTLIST coverage lines-covered    CDATA #REQUIRED>
<!ATTLIST coverage lines-valid      CDATA #REQUIRED>

I haven't checked ll

To Reproduce

Add --cobertura-xml-report to any MyPy invocation, grab the resulting XML file, and feed it to irongut/CodeCoverageSummary @ GHA.

Expected Behavior

Spec-compliant tools shouldn't crash when presented with a MyPy-produced coverage XML report advertising its compatibility with the Cobertura standard.

Actual Behavior

Tools like the irongut/CodeCoverageSummary action error out because of missing required XML attributes: irongut/CodeCoverageSummary#324. It fails upon checking for the presence of the lines-covered attribute in the <coverage> node with "Overall lines covered not found" in this case. But I looked further into their source code, and I saw that it'd also choke on missing lines-valid with "Overall lines valid not found".

I haven't checked any further but it might be a good idea to check the implementation against anything marked as #REQUIRED in said DTD spec.

Extra research

Looking into https://github.com/python/mypy/blob/fe15ee6/mypy/report.py#L597, it seems to me that the values that could be mapped to the missing attributes are already present in the class and the mapping should be straightforward:

self.total_lines -> lines-valid
self.covered_lines -> lines-covered

[x612skm]

Hey, I'm working into it! Thanks!

[webknjaz]

@hauntsaninja could you please assign this issue to @x612skm?