Clean up import structure of coercion_model

[jdemeyer]

Currently, there is a base class CoercionModel defined in element.pyx and the real coercion model is a derived class CoercionModel_cache_maps in coerce.pyx. This is explained by a comment in element.pyx:

# We define this base class here to avoid circular cimports.

However, we can get rid of this circular import by forcing element to be imported first.

Then we can move the coercion model to coerce.pyx. This has the following advantages:

1. simpler code as the superfluous base class can be deleted.

2. making more sense as everything regarding the coercion model will be in coerce.pyx

3. better performance for Cython code that cimports the coercion model as it now has access to al cdef methods and attributes, not only those from the old CoercionModel base class.

[jdemeyer]

New commits:

​8934345

Clean up import structure of coercion_model

[tscrim]

LGTM.

[git]

Branch pushed to git repo; I updated commit sha1 and set ticket back to needs_review. New commits:

​bae7f8d

Do not use SageObject for latex

[jdemeyer]

There is an issue with docbuilding.

[git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

​7d17bb4

Lazy import of latex

[git]

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

​e71573d

Do not import SageObject in sage.misc.superseded

[tscrim]

Patchbots are green.

[chapoton]

arando is not exactly green...

[tscrim]

When I was looking at it, it looked like it was morally green with some sort of misbuild with giac. However, looking at all of the failures, there are some doctests that indicate an import error from this ticket.

[jdemeyer]

I suspect (but still need to confirm) that this is just a matter of rebuilding giacpy_sage. The API of element.pxd changed, so any package cimporting that needs to be recompiled.

[git]

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

​b61bd81

Force rebuild of giacpy_sage

[jdemeyer]

A rebuild of giacpy_sage fixes it indeed.

[jdemeyer]

This again shows why patchbots should install optional packages...

[tscrim]

A real green bot. Thanks.

[embray]

Retarging tickets optimistically to the next milestone. If you are responsible for this ticket (either its reporter or owner) and don't believe you are likely to complete this ticket before the next release (8.7) please retarget this ticket's milestone to sage-pending or sage-wishlist.

[vbraun]

[sagelib-8.6] Error compiling Cython file:
[sagelib-8.6] ------------------------------------------------------------
[sagelib-8.6] ...
[sagelib-8.6] from sage.structure.parent import Parent
[sagelib-8.6] from sage.rings.all import ZZ, QQ, RDF
[sagelib-8.6] 
[sagelib-8.6] from sage.groups.perm_gps.permgroup_element cimport PermutationGroupElement
[sagelib-8.6] from sage.combinat.permutation import Permutation
[sagelib-8.6] from sage.structure.element cimport coercion_model as cm
[sagelib-8.6] ^
[sagelib-8.6] ------------------------------------------------------------
[sagelib-8.6] 
[sagelib-8.6] sage/libs/gap/element.pyx:34:0: 'sage/structure/element/coercion_model.pxd' not found

[chapoton]

@vbraun: Volker, there was a conflict with #21020, that we fixed by letting #21020 depend on the present ticket. So now you can merge either #27021 only, or both #27021 and the new version of #21020

[jdemeyer]

If you want this to be merged, it should be set back to positive review.