Parent: fixes broken (implicit) invariant between ._element_constructor and self._element_init_pass_parent

[nthiery]

In Parent, there is a (previously implicit) invariant, namely that:

self._element_init_pass_parent == guess_pass_parent(between ._element_constructor)

This invariant was broken when self._element_constructor was set from
self.element_constructor by call. This made the parent not to be
passed properly to _element_constructor.

This patch fixes this (one line), and adds a corresponding doctest.
It also includes a related trivial fix to a line that is apparently never used in coerce_maps, and adds a comment about this.

The category patch #5891 depends heavily on this one, as this way of
setting _element_constructor becomes the default one for simple
parents.

CC: @sagetrac-sage-combinat

Component: coercion

Keywords: parents, element_constructor

Author: Nicolas M. Thiéry

Reviewer: Robert Bradshaw

Merged: 4.0.1.alpha0

Issue created by migration from https://trac.sagemath.org/ticket/5979

[nthiery]

Description changed:

--- 
+++ 
@@ -1,4 +1,4 @@
-In Parent, there is an implicit invariant, namely that
+In Parent, there is a (previously implicit) invariant, namely that:
 
 	self._element_init_pass_parent == guess_pass_parent(between ._element_constructor)
 

[nthiery]

Attachment: parent-element_constructor-fix-5979-submitted.patch.gz

[nthiery]

comment:3

I should mention that sage -testall passes smoothly with sage-3.4.2-alpha0 (except for a trivial broken test in interfaces.r which also fails before applying the patch).
Haven't tried it with sage-3.4.2 final (under compilation)

[nthiery]

Description changed:

--- 
+++ 
@@ -6,10 +6,11 @@
 self._element_constructor_ by __call__. This made the parent not to be
 passed properly to _element_constructor.
 
+This patch fixes this (one line), and adds a corresponding doctest.
+It also includes a related trivial fix to a line that is apparently never used in coerce_maps, and adds a comment about this.
+
 The category patch #5891 depends heavily on this one, as this way of
 setting _element_constructor becomes the default one for simple
 parents.
 
-By the way, this patch makes a related trivial fix to a line that is
-apparently never used in coerce_maps, and adds a comment about it.
 

[mwhansen]

comment:7

Merged in 4.0.1.alpha0.