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This is a bit of a tangent, but: There are a whole bunch of places in
layout, and probably elsewhere, where we have the following catch-22:
if you have a switch statement over the values of an enumeration, gcc
and clang (with -Wall) will warn you about enumeration values that are
not handled, but only if there is no default: clause. In basically
all of the instances I know about, "default: MOZ_CRASH()" would be
appropriate, but has been omitted in the name of continuing to get
that warning (many of these enumerations do regularly get new values
added).
I had been meaning for some time to file a feature request with the
gcc people for some way to get the warning even with the default case
present, but it turns out it's already there: -Wswitch-enum.
$ cat test.c
enum Foo { Bar, Baz, Quux };
extern void a(void);
extern void b(void);
extern void c(void);
void dispatch_1(enum Foo x)
{
switch (x) {
case Bar: a(); break;
case Baz: b(); break;
default: __builtin_trap();
}
}
void dispatch_2(enum Foo x)
{
switch (x) {
case Bar: a(); break;
case Baz: b(); break;
}
}
$ gcc -Wall -Wextra -fsyntax-only test.c
test.c: In function ‘dispatch_2’:
test.c:18:3: warning: enumeration value ‘Quux’ not handled in switch
[-Wswitch]
switch (x) {
^
$ gcc -Wall -Wextra -Wswitch-enum -fsyntax-only test.c
test.c: In function ‘dispatch_1’:
test.c:9:3: warning: enumeration value ‘Quux’ not handled in switch
[-Wswitch-enum]
switch (x) {
^
test.c: In function ‘dispatch_2’:
test.c:18:3: warning: enumeration value ‘Quux’ not handled in switch
[-Wswitch]
switch (x) {
^
Similarly for clang. Dunno about MSVC, but the cases of this that I
know about are all in OS-independent code so it wouldn't be a problem.
The downside of turning this on would be that any switch statements
that *deliberately* include only a subset of the enumerators, plus a
default case, would now have to be expanded to cover all the
enumerators. I would try it and report on how unpleasant that turns
out to be, but my development box has taken to corrupting its
filesystem if I merely do a 'hg update', so I'm kind of stuck, there.
Anyone interested in trying it?
zw
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