MR11: Lazy initialization of libgap

[sagetrac-gitlab-bot]

E. Madison Bray (@embray) opened a merge request at https://gitlab.com/sagemath/sage/merge_requests/11:

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Previously the `Gap` class that implements the (effectively singleton) `libgap` instance variable in `sage.libs.gap.libgap` called `initialize()` (the function which initializes libgap for the process) in its `__init__` method.

Because of this, it was impossible to import it without causing libgap to be initialized, creating slowdown during Sage initialization.  The tradeoff is that most code in Sage that uses the libgap interface has to awkwardly use inline imports of `from sage.libs.gap.libgap import libgap` all over the place.

I would like to do away with that, especially for work on [#18267](https://github.com/sagemath/sage-prod/issues/18267).

This removes `initialize()` from `Gap.__init__()` and instead carefully places calls to `initialize()` just in the few places where it's absolutely crucial to ensure libgap is initialized first (specifically in code paths that users and developers are actually intended to use directly; it is not added directly to every single function that uses GAP objects).

This sacrifices some simplicity in implementation of the libgap interface for simplicity in using it, which I think is crucial for updating more code in Sage to use it over the pexpect interface.

Component: interfaces

Author: Erik Bray

Branch/Commit: e687ee6

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/27680

[sagetrac-gitlab-bot]

comment:2

New commits added to merge request. I updated the commit SHA-1. This was a forced push. New commits:

de4332b	Change libgap initialization to work lazily. Don't initialize() in Gap.__init__ but only just before libgap actually needs to be initialized.
e687ee6	This test no longer makes sense in light of lazy initialization of libgap

[sagetrac-gitlab-bot]

Changed commit from a756429 to e687ee6

[embray]

Changed author from E. Madison Bray to Erik Bray

[embray]

comment:3

Apparently my gitlab display name is not the same as my canonical name in Sage's build stuff. Perhaps we could add both.

[dimpase]

Reviewer: Dima Pasechnik

[dimpase]

comment:4

looks good. send it to the bots.

[vbraun]

Changed branch from u/galois/mrs/11/u/embray/libgap/lazy-initialization to e687ee6