Ensure set object descriptions are reproducible.

[lamby]

Whilst working on the Reproducible Builds effort [0], we noticed
that sphinx could generate output that is not reproducible.

In particular, the rendering of set objects in default arguments
and elsewhere is currently non-determinstic. For example:

class A_Class(object):
    a_set = {'a', 'b', 'c'}

Might be rendered as any of:

 {'a', 'b', 'c'}
 {'a', 'c', 'b'}
 {'b', 'a', 'c'}
 {'b', 'c', 'a'}
 {'c', 'a', 'b'}
 {'c', 'b', 'a'}

Patch attached that sorts the contents of sets whilst rendering.
This is parallel to the dict key sorting.

This was originally filed in Debian as #895553 [1].

[0] https://reproducible-builds.org/
[1] https://bugs.debian.org/895553

[codecov]

Codecov Report

Merging #4834 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4834      +/-   ##
==========================================
+ Coverage   82.13%   82.15%   +0.02%     
==========================================
  Files         284      289       +5     
  Lines       37801    38141     +340     
  Branches     5857     5915      +58     
==========================================
+ Hits        31046    31333     +287     
- Misses       5443     5488      +45     
- Partials     1312     1320       +8

Impacted Files	Coverage Δ
tests/test_util_inspect.py	90.7% <100%> (+0.52%)	⬆️
sphinx/util/inspect.py	73.42% <100%> (+0.44%)	⬆️
sphinx/quickstart.py	0% <0%> (ø)
sphinx/__init__.py	60% <0%> (ø)
sphinx/search/__init__.py	96% <0%> (ø)
sphinx/errors.py	70% <0%> (ø)
sphinx/apidoc.py	0% <0%> (ø)

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[tk0miya]

I think values should be also processed for dicts contains set as a value.

[mitya57]

How about calling object_description recursively? And below too, replacerepr(x) with object_description(x).

[tk0miya]

Yes, object_description(object[key]) is better to me.

[mitya57]

Ok. This was my fault when I added the dict processing code, but I hope @lamby will fix it :)

[lamby]

Pushed, including the call to object_description in the dict handling too :)

[tk0miya]

This will be failed if members are not sortable:

>>> sorted({1, 2, 'str'})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '<' not supported between instances of 'str' and 'int'

>>> sorted({1, 2, object()})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '<' not supported between instances of 'object' and 'int'

[mitya57]

So a try…except is needed, like in the dict case.

[lamby]

Good shout. Have updated with a testcase.

[tk0miya]

LGTM! I'll merge this soon.

[lamby]

Thanks all!