Provide `install_hints` for FriCAS

[slel]

Attempting to use an optional package with pexpect interface which is not installed displays whatever the method install_hints provides. This method was not provided by the FriCAS interface, resulting in a unnecessarily difficult to understand error message.

The particular error using limit with algorithm="fricas" in the original report has a different reason, which was fixed in #26068.

Old description:

When FriCAS is not present, we get the following error when trying to compute a limit using FriCAS:

sage: limit(cos(x), x=0, algorithm='fricas')
Traceback (most recent call last)
...
UnboundLocalError: local variable 'l' referenced before assignment

The error message should instead say that FriCAS was not found, and ideally hint at running sage -i fricas in the terminal.

CC: @mantepse @slel

Component: packages: optional

Keywords: FriCAS

Author: Martin Rubey

Branch/Commit: 4fa2a98

Reviewer: Frédéric Chapoton

Issue created by migration from https://trac.sagemath.org/ticket/27323

[mantepse]

comment:1

Great idea! Did you test with or without #26068?

[mantepse]

comment:2

Actually, it would make much more sense to have this message on (failed) startup of FriCAS, that is in interfaces.fricas.FriCAS.__init__ or interfaces.fricas.FriCAS._start.

Unfortunately, it is hard to uninstall fricas.

[mantepse]

comment:3

Wouldn't it be even better to do this for all Expect interfaces?

Oh, this actually exists and is called install_hints. I will provide a fix shortly.

[mantepse]

Branch: u/mantepse/check_for_fricas_when_algorithm_fricas

[mantepse]

New commits:

4828d6c

add install_hints for fricas

[mantepse]

Commit: 4828d6c

[mantepse]

Author: Martin Rubey

[7ed8c4ca-6d56-4ae9-953a-41e42b4ed313]

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

46a3fca

fix typos

[7ed8c4ca-6d56-4ae9-953a-41e42b4ed313]

Changed commit from 4828d6c to 46a3fca

[mantepse]

Description changed:

--- 
+++ 
@@ -1,3 +1,9 @@
+Attempting to use an optional package with pexpect interface which is not installed displays whatever the method `install_hints` provides.  This method was not provided by the FriCAS interface, resulting in a unnecessarily difficult to understand error message.
+
+The particular error using `limit` with `algorithm="fricas"` in the original report has a different reason, which was fixed in #26068.
+
+Old description:
+
 When FriCAS is not present, we get the following error when trying
 to compute a limit using FriCAS:

[embray]

comment:8

Ticket retargeted after milestone closed (if you don't believe this ticket is appropriate for the Sage 8.8 release please retarget manually)

[fchapoton]

comment:9

There remains a "Giac" in your "Fricas" hints..

[7ed8c4ca-6d56-4ae9-953a-41e42b4ed313]

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

4fa2a98

Giac -> FriCAS

[7ed8c4ca-6d56-4ae9-953a-41e42b4ed313]

Changed commit from 46a3fca to 4fa2a98

[mantepse]

comment:11

Thank you!

[fchapoton]

comment:12

ok, let it be

[fchapoton]

Reviewer: Frédéric Chapoton

[vbraun]

Changed branch from u/mantepse/check_for_fricas_when_algorithm_fricas to 4fa2a98