improve and document GAP and libgap memory customisation

[dimpase]

it's a FAQ, how to do this. Should be fixed, and a working solution provided.

one can test this by exporting env.vars
SAGE_GAP_MEMORY and/or SAGE_GAP_COMMAND (details in the branch`), before testing, e.g.

 $ export SAGE_GAP_MEMORY="500m"
 $ make test

CC: @kiwifb

Component: interfaces

Author: Dima Pasechnik

Branch/Commit: e6ef4fe

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/34041

[dimpase]

Author: Dima Pasechnik

[dimpase]

New commits:

b914324

allow overriding GAP memory defaults via env.vars

[dimpase]

Branch: u/dimpase/interfaces/gap_allow_memory_settings

[dimpase]

Commit: b914324

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

6a2dcc0

fix docs rst syntax

[sagetrac-git]

Changed commit from b914324 to 6a2dcc0

[mkoeppe]

comment:4

-1 on using os.getenv directly; this should go through sage.env

[mkoeppe]

comment:5

Also, the naming scheme used by sage.interfaces gives SAGE_GAP_COMMAND, not SAGE_PEXPECT_GAP_COMMAND, see #33405

[dimpase]

comment:7

Replying to @mkoeppe:

-1 on using os.getenv directly; this should go through sage.env

downstreams don't like sage.env, do they?

[mkoeppe]

comment:8

The module sage.env is our general interface to access such variables

[kiwifb]

comment:9

I love sage.env. In fact, I had my own equivalent of sage.env in sage-on-gentoo before there was one in vanilla sage. Of course that doesn't mean you should put anything and everything in there.

Now, I am not really against using os.getenv directly in code to change a behavior on the fly. But if you do, it should fall back to a sensible default or nothing if it is not defined. sage.env arguably serves as a single stop to collect such variables that ensure consistent use. But I wouldn't be to bothered if the branch was going as is.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

e6ef4fe

use sage.env, SAGE_PEXPECT_.. -> SAGE_GAP_COMMAND

[sagetrac-git]

Changed commit from 6a2dcc0 to e6ef4fe

[mkoeppe]

comment:12

Thanks for making this change, LGTM

[mkoeppe]

comment:13

(but I haven't tested it, so let's wait for the patchbot or the Build&test workflow)

[mkoeppe]

comment:15

Tested locally, seems to work fine. I was able to provoke errors in the testsuite by setting a low memory limit

[mkoeppe]

Reviewer: Matthias Koeppe

[vbraun]

Changed branch from u/dimpase/interfaces/gap_allow_memory_settings to e6ef4fe