Specify a julia binary instead of a julia prefix

[sebasguts]

and let julia collect the information about all other paths

[fingolfin]

This breaks all existing users of --with-julia, and also will complicate bisecting. At the very least, it'd be nice if we supported both giving a prefix or an executable path.

Ah, this remonds me: I think gc=julia should imply --with-julia. Not a request for this PR, it just should be done eventually

[codecov]

Codecov Report

Merging #3243 into master will decrease coverage by 7.93%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3243      +/-   ##
==========================================
- Coverage   85.09%   77.16%   -7.94%     
==========================================
  Files         695      688       -7     
  Lines      344336   338935    -5401     
==========================================
- Hits       293024   261524   -31500     
- Misses      51312    77411   +26099

Impacted Files	Coverage Δ
src/modules.h	16.66% <0%> (-83.34%)	⬇️
lib/ctbllatt.gi	4.94% <0%> (-79.62%)	⬇️
lib/ctblauto.gi	5.98% <0%> (-78.04%)	⬇️
lib/algliess.gi	5.95% <0%> (-72%)	⬇️
lib/proto.gi	13.4% <0%> (-71.14%)	⬇️
lib/ctblpope.gi	8% <0%> (-69.47%)	⬇️
lib/contfrac.gi	31.42% <0%> (-67.15%)	⬇️
src/saveload.c	3.26% <0%> (-64.58%)	⬇️
lib/lierep.gi	23.58% <0%> (-62.55%)	⬇️
lib/zlattice.gi	20.97% <0%> (-60.53%)	⬇️
... and 287 more

[coveralls]

Coverage decreased (-0.0004%) to 84.934% when pulling 29e0c60 on sebasguts:sg/use_julia_binary_for_config into c381e0c on gap-system:master.

[sebasguts]

@fingolfin I thought about making this backwards-compatible, but I decided against because I wanted to set a default.

--with-gc=julia kind of implies --with-julia= to be set, because the configure will fail. We could have a better error message, though. Or did you mean --with-julia should imply --with-gc=julia?

[fingolfin]

Backported to stable-4.10 in 3c74918

[olexandr-konovalov]

@sebasguts do you really mean [specify a prefix for a julia binary or a julia binary]?

[sebasguts]

Yes, I mean it that way.

You can either directly specify a julia binary, or its prefix, e.g., /usr/local

[olexandr-konovalov]

Ah, now I got it. Parsing plain text without parentheses or commas failed. Maybe

specify a prefix for a julia binary, or a julia binary

or

specify a julia binary or a prefix for a julia binary 

would be easier to read.

[sebasguts]

I think I understand the problem now, sorry. I will provide a PR for that.

[olexandr-konovalov]

See also #3316 for an updated comment.