Teach Test() to abort test if ctrl-C is pressed

[fingolfin]

This is a bit of a hack, but seems to work very well in practice. You can even resume the test with return if you want (but the interrupted line will still lead to diffs).

An arguably "better" (but much more complicated) solution would be to add a flag which the kernel uses to signal to the error handler that the error is a user interrupt; then we could support seamlessly resuming of the interrupted test. But this requires further work, e.g. re-redirecting input/output temporarily, saving and restoring BreakOnError and more. Not sure that this would be worth it. In the meantime, this simple solution already gets us most of the benefit.

Resolves #1879

[codecov]

Codecov Report

Merging #2900 into master will decrease coverage by <.01%.
The diff coverage is 40%.

@@            Coverage Diff             @@
##           master    #2900      +/-   ##
==========================================
- Coverage   83.73%   83.72%   -0.01%     
==========================================
  Files         680      680              
  Lines      346376   346636     +260     
==========================================
+ Hits       290046   290234     +188     
- Misses      56330    56402      +72

Impacted Files	Coverage Δ
lib/test.gi	64.31% <40%> (-0.28%)	⬇️
src/hpc/c_type1.c	83.12% <0%> (-1.29%)	⬇️
src/objects.c	80.53% <0%> (-0.69%)	⬇️
src/c_type1.c	84.04% <0%> (-0.64%)	⬇️
src/objset.c	84.49% <0%> (-0.23%)	⬇️
src/compiler.c	88.13% <0%> (-0.03%)	⬇️
src/weakptr.c	99.2% <0%> (ø)	⬆️
lib/read4.g	100% <0%> (ø)	⬆️
src/hpc/tls.h	66.66% <0%> (ø)	⬆️
src/precord.c	94.88% <0%> (ø)	⬆️
... and 8 more

[ChrisJefferson]

Could you add a brief comment that explains this code. I know it's in the git commit, but I feel this is subtle enough that it should be in the code.

[fingolfin]

Good point; comment added

[olexandr-konovalov]

That's a very handy feature! Been there hitting ctrl-C a dozen times trying to terminate the test. I've tested this with entering return, quit and QUIT in the break loop, all work as expected.

[ChrisJefferson]

I've got one more comment. Should we check the string starts with Error, user interrupt? searching through the source, there are things like "user interrupt in sleep" and "user interrupt while printing". Do we want to catch those too?

[fingolfin]

@ChrisJefferson changed to use StartsWith(res, "Error, user interrupt") as test.

[stevelinton]

Looks good to me. If we were going to do something lass hacky it would make sense to solve the bigger problem of understanding why any code execution did not complete and being able to deal with it.