Type check coverage reports need more love

[gvanrossum]

The report generating code (using command-line flags like --html-report dir or --xml-report dir) has some issues.

• There are no tests
• No report is generated for files not under the current directory
• When errors are reported, the top level index.html is not generated
• There's an undeclared dependency on lxml (Declare dependency on lxml #1001)
• The use of XSLT is dubious (Don't use XSLT in report generator #909)
• It needs docs (Document the HTML/XML report generator #912)
• Feature request to add hover text to html reports: Add hover text with explanations to html report #313

[mthuurne]

Another issue with the reports is that they are incomplete when there is cached information. I have to remove the .mypy_cache directory to get a full report, otherwise modules that have been checked before are omitted from the report.

[JukkaL]

@mthuurne That would be easy to fix by disabling incremental mode when generating reports.

[mthuurne]

Indeed adding --no-incremental helps. Would it be useful to automatically disable incremental mode when a report is requested? I would be willing to write a patch for that.

[gvanrossum]

@mthuurne If you submit a patch for that it would fix #5103. It would be very welcome!

[mthuurne]

See pull request #6076 for patch.