On Mon, Jan 22, 2018 at 11:51:18PM +0000, Elia Pinto wrote: > This patch add explicit fallthrough compiler attribute > when needed on switch case statement eliminating > the compile warning [-Werror=implicit-fallthrough=]. > It does this by means of a macro that takes into account > the versions of the compilers that include that attribute. > > The fallthrough (or clang::fallthrough) attribute is used to annotate > intentional fall-through between switch labels. > Traditionally these are marked with a specific comment, but > this attribute is meant to replace comments with a more strict > annotation, which can be checked by the compiler (gcc-7 or clang). > The flags in question were introduced in gcc 7 and are also enabled > with -Wextra.
Hrm. Your subject says "fixes compile warnings", but don't we already compile cleanly with -Wimplicit-fallthrough after my 1cf01a34ea (consistently use "fallthrough" comments in switches, 2017-09-21)? Certainly the tip of "master" seems to pass for me on both gcc 7 and clang 4. You can pump the warning up to level 5 on gcc to insist on the attribute, but I think the comments are more readable (and it is not like we have a problem with false positive comments). > It would also have been possible to introduce a specific comment > accepted by gcc 7 instead of the fallthrough attribute for this warning, > but clang does not have a similar implementation. The macro replaces > the previous, not uniform, comments and can acts as a comment itself. Interestingly clang seems to accept -Wimplicit-fallthrough, but I could not get it to actually trigger a warning, even after removing some of the existing comments. What version of clang are you using? I'm certainly puzzled by the behavior I'm seeing. > diff --git a/apply.c b/apply.c > index 321a9fa68..a22fb2881 100644 > --- a/apply.c > +++ b/apply.c > @@ -1450,7 +1450,7 @@ static void recount_diff(const char *line, int size, > struct fragment *fragment) > switch (*line) { > case ' ': case '\n': > newlines++; > - /* fall through */ > + GIT_FALLTHROUGH; Ugh, the semi-colon there makes it look like it's actual code. If we go this route, I wonder if it's worth hiding it inside the macro. -Peff