[proposal] test coverage output

[RossComputerGuy]

It would be useful to have like a dot graphs generation or HTML output generation of a module's test coverage. Maybe it could show which lines have test failures along with the error? A lot of test frameworks have this ability and so having this could make it easier to determine what has been tested and what has not been tested.

[squeek502]

If you haven't seen it, here's a way to get coverage with status-quo Zig: https://zig.news/squeek502/code-coverage-for-zig-1dk1

Note also that both comptime and unreferenced functions make "accurate" coverage tricky.

Somewhat related (since built-in coverage would depend on instrumentation): #5484

[RossComputerGuy]

@squeek502 Yeah those do look nice but I believe something in Zig itself would be better imo. Those look like they rely on debug info and the symbol table. Using the actual Zig AST and/or the test runner could give better test coverage output.

[VisenDev]

Possibly related

#17821

[squeek502]

Duplicate of #352