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* [Bug preprocessor/66322] New: Linus Torvalds: -Wswitch-bool produces dubious warnings, fails to notice really bad things
@ 2015-05-28  6:51 t.artem at mailcity dot com
  2015-05-28  8:14 ` [Bug c/66322] " manu at gcc dot gnu.org
                   ` (8 more replies)
  0 siblings, 9 replies; 10+ messages in thread
From: t.artem at mailcity dot com @ 2015-05-28  6:51 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66322

            Bug ID: 66322
           Summary: Linus Torvalds: -Wswitch-bool produces dubious
                    warnings, fails to notice really bad things
           Product: gcc
           Version: 5.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: t.artem at mailcity dot com
  Target Milestone: ---

From: https://lkml.org/lkml/2015/5/27/941

Btw, I'd actually like to see (possibly optionally) a warning for enum
types there too. Exactly because *type* based warnings very much make
sense, regardless of number of cases.

For example, try this:

    #include <stdbool.h>
    #include <stdio.h>

    enum a { one, two };
    int t(bool b, enum a e)
    {
        switch (b) {
        case true:
            printf("No arguments\n");
            /* fallthrough */
        case false:
            printf("\n");
        }
        switch (e) {
        case 0:
            printf("one");
            break;
        case two:
            printf("two");
            break;
        }
        return 0;
    }
and I'd argue that gcc-5.1 warns about TOTALLY THE WRONG THING.

It does that *stupid* warning:

    warning: switch condition has boolean value [-Wswitch-bool]

which is just idiotic and wrong.

The case statements are clearly boolean, there is absolutely nothing
wrong with that switch, and a compiler that warns about it is just
being f*cking moronic.

In contrast, that second switch() statement with the "case 0:" is
actually something that might well be worth warning for. I'd argue
that the code would clearly be more legible if it used "case one:"
instead.

So the new warning in gcc-5 seems to be just stupid. In general,
warnings that encourage you to write bad code are stupid. The above

    switch (boolean) {
    case true:
is *good* code, while the gcc documentation suggests that you should
cast it to "int" in order to avoid the warning, but anybody who
actually thinks that

    switch ((int)boolean) {
    switch 1:
is better, clearly has absolutely zero taste and is just objectively wrong.

Really. A warning where the very *documentation* tells you to do
stupid things is stupid.


^ permalink raw reply	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2022-01-11 21:00 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-05-28  6:51 [Bug preprocessor/66322] New: Linus Torvalds: -Wswitch-bool produces dubious warnings, fails to notice really bad things t.artem at mailcity dot com
2015-05-28  8:14 ` [Bug c/66322] " manu at gcc dot gnu.org
2015-05-28  9:29 ` mpolacek at gcc dot gnu.org
2015-05-28  9:38 ` mpolacek at gcc dot gnu.org
2015-05-28 10:31 ` nszabolcs at gmail dot com
2015-05-28 11:37 ` manu at gcc dot gnu.org
2015-06-22 18:16 ` mpolacek at gcc dot gnu.org
2015-06-29 13:13 ` mpolacek at gcc dot gnu.org
2015-10-22  9:14 ` mpolacek at gcc dot gnu.org
2022-01-11 21:00 ` pinskia at gcc dot gnu.org

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