a problem with GAP package loading mechanism

[mohamed-barakat]

@ChrisJefferson's packages json fails to load:

julia> using GAP
julia> LoadPackageAndExposeGlobals( "json", Main, all_globals = true )
ERROR: cannot load package json
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] #LoadPackageAndExposeGlobals#9(::Bool, ::Bool, ::typeof(LoadPackageAndExposeGlobals), ::String, ::Module) at /Users/mo/.julia/dev/GAP/src/gap2.jl:116
 [3] (::getfield(GAP, Symbol("#kw##LoadPackageAndExposeGlobals")))(::NamedTuple{(:all_globals,),Tuple{Bool}}, ::typeof(LoadPackageAndExposeGlobals), ::String, ::Module) at ./none:0
 [4] top-level scope at REPL[2]:1

[ChrisJefferson]

Is there any way for me to understand what's actually going wrong? :)

[ThomasBreuer]

@mohamed-barakat I cannot reproduce this behaviour.
The error message comes from a call GAP.EvalString( "LoadPackage( \"json\" )" ).
If you start the GAP in question directly and call LoadPackage( "json" ), does the package load?
If not then perhaps recompiling the package helps.

[mohamed-barakat]

Thank you @ThomasBreuer for your comment. The package json properly loads in ~/.julia/dev/GAP/gap.sh but fails in julia:

~/.julia/dev/GAP (master)$ ./gap.sh
 ┌───────┐   GAP 4.10dev-2263-g9f330be of today
 │  GAP  │   https://www.gap-system.org
 └───────┘   Architecture: x86_64-apple-darwin18.6.0-julia64-kv7
 Configuration:  gmp 6.1.2, Julia GC, Julia 1.2.0
 Loading the library and packages ...
 Packages:   AClib 1.3.1, Alnuth 3.1.1, AtlasRep 2.1.0, AutoDoc 2019.07.24, AutPGrp 1.10.1, Browse 1.8.8, Carat 2.2.3, CRISP 1.4.4, Cryst 4.1.20, CrystCat 1.1.9,
             CTblLib 1.2.2, FactInt 1.6.2, FGA 1.4.0, Forms 1.2.5, GAPDoc 1.6.3, genss 1.6.6, IO 4.7.0, IRREDSOL 1.4, LAGUNA 3.9.3, orb 4.8.2, Polenta 1.3.8,
             Polycyclic 2.14, PrimGrp 3.3.2, RadiRoot 2.8, recog 1.3.2, ResClasses 4.7.2, SmallGrp 1.3, Sophus 1.24, SpinSym 1.5.1, TomLib 1.2.8, TransGrp 2.0.4,
             utils 0.65
 Try '??help' for help. See also '?copyright', '?cite' and '?authors'
gap> LoadPackage( "json" );
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Loading  json 2.0.0 (Reading and Writing JSON)
by Christopher Jefferson (http://caj.host.cs.st-andrews.ac.uk/).
Homepage: https://gap-packages.github.io/json/
Report issues at https://github.com/gap-packages/json/issues
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
true

julia> using GAP
 ┌───────┐   GAP 4.10dev-2263-g9f330be of today
 │  GAP  │   https://www.gap-system.org
 └───────┘   Architecture: x86_64-apple-darwin18.6.0-julia64-kv7
 Configuration:  gmp 6.1.2, Julia GC, Julia 1.2.0
 Loading the library and packages ...
 Packages:   GAPDoc 1.6.3, PrimGrp 3.3.2, SmallGrp 1.3, TransGrp 2.0.4
 Try '??help' for help. See also '?copyright', '?cite' and '?authors'

julia> GAP.Globals.SetInfoLevel(GAP.Globals.InfoPackageLoading,4);

julia> GAP.Globals.LoadPackage( GAP.julia_to_gap("json") )
#I  json: entering LoadPackage
#I  json: PackageAvailabilityInfo for version 2.0.0
#I  json: kernel functions for json are not available.
#I  json: PackageAvailabilityInfo: the AvailabilityTest function returned false
#I  json: PackageAvailabilityInfo: no installed version fits
#I  json: return from LoadPackage, package is not available
GAP: fail

[mohamed-barakat]

Together with @ThomasBreuer we figured out that GAP in julia is trying to load json from another path which was compiled for a different GAP although both versions of json coincide and the path for the correct json version is appearing first in EXTRA_GAPROOT.

I will therefore change the title of this issue.

[fingolfin]

If you have two copies of the same GAP package, with the same version in each, then GAP will pick one, and ignore the other, period. There is nothing GAP.jl can do about this. If at all, this is a GAP issue. But frankly, I am not sure how I'd deal with it on the GAP side either -- in the end, this is a very rare issue that only affects people who dabble with custom GAP root paths -- that's a tiny fraction of our user base, and all "power users".

I.e.: "Then don't do that!" ;-)

That said, if people have suggestions how to deal with this, then opening an issue at the GAP repository for this would be worthwhile.

But this is out of scope for GAP.jl

[mohamed-barakat]

I agree.