Fixed a bug in intersphinx failure reporting

[lsaffre]

Subject: fix a bug in intersphinx reporting failures

I had a published Sphinx doctree at http://de.presto.lino-framework.org with an invalid :xfile:objects.inv file so that intersphinx was not able to read it. It said::

ValueError: unknown or unsupported inventory version: ValueError(u'invalid inventory header: ',)

This message is not the problem (I guess it was because that site was generated with another Sphinx version, but that's unrelevant). My problem is that this error was never reported. It was never reported because :func:sphinx.ext.intersphinx.fetch_inventories does something forbidden::

try:
   ...
except Exception as err:
    err.args = ('intersphinx inventory %r not fetchable due to %s: %s',
                inv, err.__class__, err)  # LS20190306
    raise
try:
    ...
except Exception as err:
    err.args = ('intersphinx inventory %r not readable due to %s: %s',
                inv, err.__class__.__name__, err)  # LS20190306

To fix my problem, I replaced both lines::

    err.args = (msgtpl, inv, err.__class__, err)

by::

    err.args = (msgtpl, inv, err.__class__, str(err))

The problem might occur only when there is an additional exception "intersphinx inventory has moved" involved. Here is the output before the bugfix::

loading intersphinx inventory from http://de.presto.lino-framework.org...
intersphinx inventory has moved: http://de.presto.lino-framework.org -> http://de.presto.lino-framework.org/
WARNING: failed to reach any of the inventories with the following issues:
intersphinx inventory 'http://de.presto.lino-framework.org' not readable due to ValueError: ('intersphinx inventory %r not readable due to %s: %s', 'http://de.presto.lino-framework.org', 'ValueError',  ValueError(...))

Another problem fixed en passant was that intersphinx later reports every failure as a separate call to :func:warning and when tolerate_warnings is False, we see only the first warning.

[codecov]

Codecov Report

Merging #6139 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #6139      +/-   ##
==========================================
- Coverage   82.67%   82.67%   -0.01%     
==========================================
  Files         272      272              
  Lines       39301    39300       -1     
  Branches     5877     5877              
==========================================
- Hits        32493    32492       -1     
  Misses       5473     5473              
  Partials     1335     1335

Impacted Files	Coverage Δ
sphinx/ext/intersphinx.py	88.23% <100%> (-0.06%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b58d0e8...c0ed808. Read the comment docs.

[tk0miya]

LGTM. But could you rebase this into 1.8 branch? Then I'll merge this into next release.
Thanks,

[lsaffre]

Seems that my brain is too small for this task. But I tried and created a new pull request #6148
Does this help?

[tk0miya]

Merged #6148 instead.