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From: Jonathan Wakely <jwakely.gcc@gmail.com>
Date: Mon, 16 Aug 2021 12:55:39 +0100
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Subject: What should a std::error_code pretty printer show?
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I'm adding a GDB printer for std::error_code.What I have now prints
the category name as a quoted string, followed by the error value:

{"system": 0}
{"system": 1234}

If the category is std::generic_category() then it also shows the
strerror description:

{"generic": 13 "Permission denied"}

But I'd also like it to show the errno macro, but I'm not sure what's
the best way to show it.

Does this seem OK?

{"generic": 13 EACCES "Permission denied"}

I think that's a bit too verbose.

Would {"generic": EACCES} be better? You can always use ec.value() to
get the numeric value, and strerror to get the description if you want
those.