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#75964
Switching the Emacs build to -Wswitch-enum in src/
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"Eli Zaretskii" <eliz <at> gnu.org> writes:
>> Date: Sun, 02 Feb 2025 12:50:15 +0000
>> From: Pip Cet <pipcet <at> protonmail.com>
>> Cc: 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>
>>
>> Looking at bidi.c, I find bidi_get_type, which is essentially a single
>> switch statement, much easier to read than the new long switch statement
>> in in bidi_find_bracket_pairs:
>>
>> switch (bidi_it->type)
>> {
>> case STRONG_L:
>> flag = ((embedding_level & 1) == 0
>> ? FLAG_EMBEDDING_INSIDE
>> : FLAG_OPPOSITE_INSIDE);
>> l2r_seen = true;
>> break;
>> case STRONG_R:
>> case WEAK_EN:
>> case WEAK_AN:
>> flag = ((embedding_level & 1) == 1
>> ? FLAG_EMBEDDING_INSIDE
>> : FLAG_OPPOSITE_INSIDE);
>> r2l_seen = true;
>> break;
>> case UNKNOWN_BT:
>> case WEAK_BN:
>> case NEUTRAL_B:
>> case STRONG_AL:
>> case LRE:
>> case LRO:
>> case RLE:
>> case RLO:
>> case PDF:
>> case LRI:
>> case RLI:
>> case FSI:
>> case PDI:
>> case WEAK_ES:
>> case WEAK_ET:
>> case WEAK_CS:
>> case WEAK_NSM:
>> case NEUTRAL_S:
>> case NEUTRAL_WS:
>> case NEUTRAL_ON:
>> default: break;
>> }
>
> This is an example of code where some value of an enumeration need
> special handling, and the rest don't need any handling at all. IMO,
> we should ask ourselves what are we trying to accomplish by spelling
> out all of the "other" values instead of just 'default'? If we only
> care for a handful of values, what kind of errors could slip us if we
> use 'default'?
As someone who's not very familiar with the bidi code, I would feel most
comfortable if this switch, with all cases, were in an inline function
which decides whether we set l2r_seen, r2l_seen, or neither, in this
context. Ideally, in my case, with further comments, though trying to
understand this code without studying the Unicode Bidirectional
Algorithm will always be foolish...
However, I think bidi.c is the file I most strongly feel would not
benefit from -Wswitch-enum.
>> I think that could be rewritten to be more readable in a number of ways,
>> including, of course, putting a #pragma in.
>
> IMO, the way it should be rewritten (or not) depends on the answer to
> the above question.
Agreed.
Pip
This bug report was last modified 127 days ago.
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