GNU bug report logs - #75964
Switching the Emacs build to -Wswitch-enum in src/

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Message #170 received at 75964 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Pip Cet <pipcet <at> protonmail.com>
Cc: acorallo <at> gnu.org, eggert <at> cs.ucla.edu, 75964 <at> debbugs.gnu.org,
 monnier <at> iro.umontreal.ca, stefankangas <at> gmail.com
Subject: Re: bug#75964: Switching the Emacs build to -Wswitch-enum in src/
Date: Tue, 04 Feb 2025 14:24:32 +0200

> Date: Mon, 03 Feb 2025 21:15:38 +0000
> From: Pip Cet <pipcet <at> protonmail.com>
> Cc: Eli Zaretskii <eliz <at> gnu.org>, eggert <at> cs.ucla.edu, 75964 <at> debbugs.gnu.org, stefankangas <at> gmail.com, Andrea Corallo <acorallo <at> gnu.org>
> 
> "Stefan Monnier" <monnier <at> iro.umontreal.ca> writes:
> 
> >> enum ABC abc;
> >> switch (abc) {
> >> case A:
> >>   /* handle case A */
> >>   break;
> >> default:
> >>   /* we know this must be case C */
> >>   /* handle case C */
> >>   break;
> >> }
> >
> > I think this just suggests we should refrain from using `default:`
> 
> Switching over an enum without a default: label will generate
> fall-through code, for those cases in which the enum variable has a
> value that's not in the enumeration.

What is "fall-through code" in this context, and why is it bad that
the compiler will generate such code?

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