Add command line option --packagedirs and GAP function ExtendPackageDirectories() to make it easier to use custom packages

[lgoettgens]

Resurrection of and thus closes #933. Work towards oscar-system/GAP.jl#1092.

Please see the above linked PRs/issues for the motivation of this change.

This currently only contains the changes from @fingolfin in 2016 and some documentation adaptions. I am still working on the cmd line option.

I noticed that for root dirs the corresponding function is called ExtendRootDirectories(), but they are stored in GAPInfo.RootPaths. In #933, there was a mix of GAPInfo.PackageDirectories and GAPInfo.PackagePaths. Do you have any preference here @fingolfin ?

[lgoettgens]

This now has a cmd line argument part for --packagedirs. It does not have the semicolon magic as -l, as it is not clear to me what this should mean in this case. Should it skip the pkg subdirs of the gap roots? But what is with roots added later using ExtendRootDirectories()?

And what is there else to do here?

[fingolfin]

Thank you for working on this! I have no preference between GAPInfo.PackageDirectories and GAPInfo.PackagePaths

[ThomasBreuer]

The code looks o.k., modulo the hints that were already given.
I have added a few comments about the documentation.

[ThomasBreuer]

I have suggested changes to the description of the new command line option. (I hope I got it right.)

[fingolfin]

Thank you, looks great to me!

Perhaps we can get some native speakers like @james-d-mitchell or @ChrisJefferson to have a look at the text before merging, so I'll wait a bit with that (but in the end, things can be improved in a follow-up PR, too)

[schnellecom]

I also think that this addition is valuable, in particular during the development of GAP packages.
In that scenario: What happens, if a package is loaded through --packagedirs, then the package is changed and then loaded again? I can imagine that if the package is completely reloaded this would be helpful for testing newly implemented parts of a package in developement.

[fingolfin]

Reloading packages is completely unrelated to this PR, though, and not generally supported by GAP. (Limited support for reloading individual files exists; but not for changing from where a package is loaded)

[fingolfin]

There is also a CI failure, probably a direct result of the changes in here and the solution may be to adjust the test, once we understand why it changed:

  ########> Diff in /home/runner/work/gap/gap/tst/testinstall/package.tst:
  635
  # Input is:
  Last( GAPInfo.PackagesInfo.mockpkg ).InstallationPath =
       GAPInfo.PackagesLoaded.mockpkg[1];
  # Expected output:
  true
  # But found:
  false
  ########

That said, GAP CI is currently broken (see issue #5884)

[lgoettgens]

This error only occurrs in some of the CI jobs. At least CI / testinstall - - ubuntu-latest runs this as well and succeeds. Furthermore, I cannot reproduce this locally (at lest not with ./gap tst/testinstall.g) on my Arch Linux system

[ThomasBreuer]

I cannot reproduce this problem locally.
If we have no better idea then we could change the testfile for debugging purposes, such that we see the objects
List( GAPInfo.PackagesInfo.mockpkg, x -> x.InstallationPath ) and GAPInfo.PackagesLoaded.mockpkg.

[fingolfin]

Note that in the CI setup there may be additional symlinks to/for pkg subdirs, which may affect this:

dev/ci.sh:103:    rm -f pkg && ln -sf . pkg
dev/ci.sh:320:    ln -s $SRCDIR/pkg $GAPPREFIX/share/gap/pkg

Perhaps one or both should go resp. be replaced by usage of --packagedirs?

BTW, there are also failures in the GAP.jl tests

[lgoettgens]

Note that in the CI setup there may be additional symlinks to/for pkg subdirs, which may affect this:

dev/ci.sh:103:    rm -f pkg && ln -sf . pkg
dev/ci.sh:320:    ln -s $SRCDIR/pkg $GAPPREFIX/share/gap/pkg

Perhaps one or both should go resp. be replaced by usage of --packagedirs?

Thanks for the hint. Indeed, the first one should use --packagedirs instead.

BTW, there are also failures in the GAP.jl tests

These are due to the way I used to interpret a packagedir both as the directory of a package and as a directory that contains packages with directories. This should be fixed in the most recent commit.

[fingolfin]

I applied a few minor tweaks to the documentation and even more minor ones to the code. Assuming CI passes I think this is good to go.