Add another doctest to connecting conversion maps

[lftabera]

between 4.7.x and 5.x series, the following error was introduced:

K = NumberField([x^2-2, x^2-3], 'a,b')
M = K.absolute_field('c')
M_to_K, K_to_M = M.structure()
M.register_coercion(K_to_M)
K.register_coercion(M_to_K)
M.coerce_map_from(QQ)
...
UnboundLocalError: local variable 'connecting' referenced before assignment

This error was fixed in #12919. We propose to add a new test to that fix.

CC: @simon-king-jena

Component: coercion

Author: Simon King, Luis Felipe Tabera Alonso

Reviewer: Keshav Kini, Marco Streng

Merged: sage-5.3.beta2

Issue created by migration from https://trac.sagemath.org/ticket/12990

[lftabera]

comment:1

The solution was found by Simon King discussing #12269

[lftabera]

Author: Simon King, Luis Felipe Tabera Alonso

[nbruin]

comment:3

OK, nevermind attachment: trac_12990.patch. Overlapping time windows! Just go with the first patch. The typo was introduced in #7420, which was merged in 4.3. Apparently changes after 4.7.1 made it so that the example in the ticket activates this code path.

[kini]

comment:4

patchbot: apply connecting.patch

[kini]

Reviewer: Keshav Kini

[kini]

comment:5

Looks good to go.

[jdemeyer]

comment:6

Looks like like a duplicate of #12919.

[kini]

comment:7

Well would you look at that... hmm. Maybe we can keep the doctest from this patch. I've posted a comment on #12919.

[lftabera]

comment:8

Yes, whis is a clear duplicate of #12919, however, I would like to keep also the doctest of this patch, 12919 doctest is a an ad-hoc class for testing the bug. In this patch is a "real-life" situation where the bug is triggered.

Should I clear the patch to keep only the doctest and possibli be merged?

[kini]

comment:9

Sounds good to me.

[mstreng]

Changed reviewer from Keshav Kini to Keshav Kini, Marco Streng

[mstreng]

comment:11

Attachment: connecting.patch.gz

[kini]

comment:12

Whoops, forgot about this ticket. Thanks for the positive review, mstreng.

[jdemeyer]

Merged: sage-5.3.beta2