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.
