Add errors on separate lines for coverage

[MichaelChirico]

if (FALSE) error("failed");

Is not caught by Codecov because it doesn't build a proper AST for C code. So we have to put error branches on their own line to be properly detected by Codecov.

Only done this for error so far. A few more patterns could be included:

• warning
• STOP in fread.c
• Verbose output? Rprintf etc, not sure how important it is to cover these... I see about 100 more lines with DTPRINT and Rprintf
• ...

[codecov]

Codecov Report

Merging #4301 into master will increase coverage by <.01%.
The diff coverage is 99.74%.

@@            Coverage Diff             @@
##           master    #4301      +/-   ##
==========================================
+ Coverage   99.61%   99.61%   +<.01%     
==========================================
  Files          72       72              
  Lines       13916    14088     +172     
==========================================
+ Hits        13862    14034     +172     
  Misses         54       54

Impacted Files	Coverage Δ
src/fcast.c	100% <ø> (ø)	⬆️
src/ijoin.c	95.29% <ø> (ø)	⬆️
src/nafill.c	100% <ø> (ø)	⬆️
src/openmp-utils.c	100% <100%> (ø)	⬆️
src/assign.c	100% <100%> (ø)	⬆️
src/init.c	100% <100%> (ø)	⬆️
src/rbindlist.c	100% <100%> (ø)	⬆️
src/vecseq.c	100% <100%> (ø)	⬆️
src/dogroups.c	100% <100%> (ø)	⬆️
src/fmelt.c	99.22% <100%> (+0.21%)	⬆️
... and 15 more

---

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[MichaelChirico]

wow! 62% (176/285) of these branches were uncovered. looks like it's paying off already in terms of understanding spurious coverage.

[MichaelChirico]

!dec %chin% c('.', ',') is implied incorrect by L1179 of fread.c @ master:

dec='' not allowed. Should be '.' or ','

?fread is not as strict:

The decimal separator as in utils::read.csv. If not "." (default) then usually ",". See details.

Took a conservative approach for now, and blocked !dec %chin% c(',', '.'). But that broke two tests (1440 and 1444.2 here).

dec='1' and dec='*' ran without errors... happy to restore this to work, and change the error/message found in fread.c.

[MichaelChirico]

This function binary( isn't used anywhere... just for debugging?

[mattdowle]

Yes

[MichaelChirico]

Don't know how to cover this line so leaving this PR here:

      if (!firstJumpEnd)
        STOP(_("Single column input contains invalid quotes. Self healing only effective when ncol>1"));

[MichaelChirico]

Heads up that there will be a ton of conflicts between this one and #4306 (I count 20 at the moment). Let's merge this one first, since this one adds a bunch of internal errors.

[MichaelChirico]

@jangorecki any thoughts on the third point -- should we put verbose messaging on its own line as well?

[jangorecki]

@MichaelChirico I don't think it is so important. I would just keep that in mind when coding new stuff, but not necessarily touch all the existing one.

[mattdowle]

What would it take to make C coverage cover branches within one line; i.e. like R coverage already does?
I don't know which tool that would be -- whether it's something inside covr or inside gcc toolchain itself, @jimhester?
But that's the root cause. There would be much more bang-for-the-time to work on that? That way, coverage for all R packages using C code would be improved, not just data.table.
If there is something deeply insurmountable about doing that (e.g. a covr, gcc or clang developer stating that it's not just difficult but not possible in C) then I'd be much more comfortable splitting all our C lines given that justification I can point to. But I hope it's actually possible to get coverage within same-line C branches implemented. That would be awesome. Could even lead to a paper and conference presentation.