Refactor sage-location

[jdemeyer]

Some various clean-up of sage-location, in particular:

1. Don't use realpath() or abspath() everywhere. Just once should be more than sufficient.
2. Merge initialize_pkgconfig_files() and update_pkgconfig_files().
3. Improve the logic, i.e. install_moved() should not write the processor flags.
4. Improve structure by creating a new top-level function sage_relocate() which then calls the other functions.
5. Better documentation.

Follow-up tickets: #13407, #5155.

[ohanar]

According to the FHS, the location_file and cflags_file should live in SAGE_LOCAL/var/lib. Since you are already touching those lines, do you think we could set the location_file to SAGE_LOCAL/var/lib/sage/current-location.txt (and similarly for cflags_file)?

[jdemeyer]

Replying to ohanar:

According to the FHS, the location_file and cflags_file should live in SAGE_LOCAL/var/lib. Since you are already touching those lines, do you think we could set the location_file to SAGE_LOCAL/var/lib/sage/current-location.txt (and similarly for cflags_file)?

Not on this ticket.

[jdemeyer]

Replying to ohanar:

According to the FHS, the location_file and cflags_file should live in SAGE_LOCAL/var/lib.

I don't think there is /usr/var or /usr/local/var. I would vote for local/etc instead (which does exist, although it's rarely used).

[ohanar]

Replying to jdemeyer:

Replying to ohanar:

According to the FHS, the location_file and cflags_file should live in SAGE_LOCAL/var/lib.

I don't think there is /usr/var or /usr/local/var. I would vote for local/etc instead (which does exist, although it's rarely used).

-1, etc should be used for text configuration -- these files aren't configuration files, they are storing state information (which is precisely what var/lib is for).

At least according to the FHS, there shouldn't be an /usr/etc either. The FHS doesn't really cover prefixed environments, so I think it is fair to use relevant directories in / when necessary. (For instance, IMO, SAGE_ROOT/ipython/* should probably be installed into SAGE_LOCAL/etc somewhere).

[jdemeyer]

Replying to ohanar:

-1, etc should be used for text configuration -- these files aren't configuration files, they are storing state information (which is precisely what var/lib is for).

At least according to the FHS, there shouldn't be an /usr/etc either. The FHS doesn't really cover prefixed environments, so I think it is fair to use relevant directories in / when necessary. (For instance, IMO, SAGE_ROOT/ipython/* should probably be installed into SAGE_LOCAL/etc somewhere).

OK, /usr/etc isn't official either, so that part of the argument is moot.

Still (I know, bikeshedding) I think the description of etc as read-only configuration files fits these files much better than var's "state information". It's something which under normal usage of Sage does not change. It's equally read-only as the content of $SAGE_ROOT/local/bin.

Regardless, I prefer not to change this in this ticket because other tickets depend on it. I'd rather finish #5155 first and then think about where to put these files.

[dimpase]

Very nice. I noticed quite a speedup upon trying to move installations around.

[jdemeyer]

Replying to dimpase:

I noticed quite a speedup upon trying to move installations around.

A speed-up was never the intention of this ticket. Perhaps the speed-up is because files are opened only once instead of twice?