C/C++, fix lack of error stringification

[jakobandersen]

Feature or Bugfix

• Bugfix

Purpose

The switch to the new'ish logging facilities in the C and C++ domains was not quite correct. In a few places the logged exception was not stringified.

Detail

• Fixes TypeError in sphinx logging building CPython docs with Sphinx 3.0 #7423, hopefully. I have not yet been able to reproduced without venv.

[tk0miya]

I consider this is a bug of our logging module. So the following fix is better to me:

diff --git a/sphinx/util/logging.py b/sphinx/util/logging.py
index fbf161ec0..53053faaf 100644
--- a/sphinx/util/logging.py
+++ b/sphinx/util/logging.py
@@ -412,7 +412,7 @@ class WarningIsErrorFilter(logging.Filter):
                 message = record.msg  # use record.msg itself

             if location:
-                raise SphinxWarning(location + ":" + message)
+                raise SphinxWarning(location + ":" + str(message))
             else:
                 raise SphinxWarning(message)
         else:

What do you think?

[jakobandersen]

I looked a bit more into it, and it looks like the fix of @tk0miya is indeed the proper one.
While the top-level functions of the Python logging module definitely says
The documentation of the Python logging module says the first argument must be a format string (https://docs.python.org/3/library/logging.html#logging.debug), but that seems to be incorrect (https://docs.python.org/3/library/logging.html#logging.LogRecord.getMessage).
@tk0miya, do you your fix ready? otherwise I can make a new PR.

[tk0miya]

Okay, I'll do it later.