problem when installing the package programmatically

[ThomasBreuer]

It makes sense to install a new version of a GAP package of which an older version is already loaded in the current GAP session.
If one installs the package with PackageManager's InstallPackage via a URL then PackageManager notices that the package documentation needs to be processed, and tries to build the package documentation.

Now the following happens in the case of the recog package.
The file makedoc.g reads the file regen_doc.g, and this file contains a check whether a perhaps already loaded version of recog has the same installation path as the version that is currently going to get installed; if not then an error is thrown.

This means that it is not possible to load one version of recog (which happens when GAP starts) and then to install a newer version of recog with InstallPackage via a URL.

I think that packages should not throw an error in the above situation, and that we should perhaps document this.

[ThomasBreuer]

Now I understand what is going on:

The code in regen_doc.g creates/updates some files in the doc directory, and the intended contents of these files depends on the source code of recog.
(Is it allowed at all to write files inside the package directory?)

What about the following:
We change makedoc.g such that it checks whether recog is already loaded. If yes then we start a new instance of GAP without packages, and read makedoc.g into this new GAP session.

Thus makedoc.g could look as follows.

if fail = LoadPackage("AutoDoc", ">= 2019.07.03") then
    ErrorNoReturn("AutoDoc 2019.07.03 or newer is required");
fi;

# if the current GAP session has already loaded recog then start a new session.
if IsBound( GAPInfo.PackagesLoaded.recog ) then
  Exec( Concatenation( GAPInfo.SystemCommandLine[1], " -A -b -c 'Read(\"./makedoc.g\");'" ) );
  QuitGap(true);
fi;

Read("regen_doc.g");

[...] # Here the data and commands for `AutoDoc` follow.

QuitGap(true);

(The QuitGap calls are new, I think they are in general recommended for makedoc.g.)

[ThomasBreuer]

After a discussion with @fingolfin:

• The recog package is the wrong place to solve this problem.
  It would be better if the PackageManager package always creates package documentation in a fresh GAP session in which no packages are loaded.
• One problem with the idea proposed above is that GAPInfo.SystemCommandLine does not contain the necessary information if one starts the GAP session from a Julia session, via the GAP.jl package: Currently GAPInfo.SystemCommandLine[1] is an empty string in this case.
  Thus we have to provide a solution that enables PackageManager to start a fresh GAP session.