| Message ID | 20230831071945.GE3197751@coredump.intra.peff.net (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | more unused parameters in parseopt callbacks | expand |
Jeff King <peff@peff.net> writes: > There are a few parse-option callbacks that do not look at their "unset" > parameters, but also do not set PARSE_OPT_NONEG. At first glance this > seems like a bug, as we'd ignore "--no-if-exists", etc. > > But they do work fine, because when "unset" is true, then "arg" is NULL. > And all three functions pass "arg" on to helper functions which do the > right thing with the NULL. Yuck. That is ugly. > Note that this shortcut would not be correct if any callback used > PARSE_OPT_NOARG (in which case "arg" would be NULL but "unset" would be > false). But none of these do. That is even uglier. Unlike the BUG_ON_OPT_NEG() and BUG_ON_OPT_ARG() that catch discrepancies between options[] flags and the expectation by the callback function, there is no way for us to protect against such mistakes? > So the code is fine as-is. But we'll want to mark the unused "unset" > parameters to quiet -Wunused-parameter. OK. Thanks. > Signed-off-by: Jeff King <peff@peff.net> > --- > builtin/interpret-trailers.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/builtin/interpret-trailers.c b/builtin/interpret-trailers.c > index 6aadce6a1e..a5f9adf6b9 100644 > --- a/builtin/interpret-trailers.c > +++ b/builtin/interpret-trailers.c > @@ -24,19 +24,19 @@ static enum trailer_if_exists if_exists; > static enum trailer_if_missing if_missing; > > static int option_parse_where(const struct option *opt, > - const char *arg, int unset) > + const char *arg, int unset UNUSED) > { > return trailer_set_where(opt->value, arg); > } > > static int option_parse_if_exists(const struct option *opt, > - const char *arg, int unset) > + const char *arg, int unset UNUSED) > { > return trailer_set_if_exists(opt->value, arg); > } > > static int option_parse_if_missing(const struct option *opt, > - const char *arg, int unset) > + const char *arg, int unset UNUSED) > { > return trailer_set_if_missing(opt->value, arg); > }
On Thu, Aug 31, 2023 at 10:04:09AM -0700, Junio C Hamano wrote: > Jeff King <peff@peff.net> writes: > > > There are a few parse-option callbacks that do not look at their "unset" > > parameters, but also do not set PARSE_OPT_NONEG. At first glance this > > seems like a bug, as we'd ignore "--no-if-exists", etc. > > > > But they do work fine, because when "unset" is true, then "arg" is NULL. > > And all three functions pass "arg" on to helper functions which do the > > right thing with the NULL. > > Yuck. That is ugly. Yep. I wondered about adding a comment here warning about the situation, but it felt kind of content-less. Something like: /* if unset, arg is NULL and handled below */ trailer_set_where(opt->value, arg); > > Note that this shortcut would not be correct if any callback used > > PARSE_OPT_NOARG (in which case "arg" would be NULL but "unset" would be > > false). But none of these do. > > That is even uglier. Unlike the BUG_ON_OPT_NEG() and BUG_ON_OPT_ARG() > that catch discrepancies between options[] flags and the expectation > by the callback function, there is no way for us to protect against > such mistakes? I guess it would be something like: if (!unset && !arg) BUG("unexpected use of PARSE_OPT_OPTARG"); I think it is less important than those other ones, though, because the mistake here is the OPT_CALLBACK declaration adding a flag that the callback is not prepared to handle. Whereas in the other ones, the bug is that the declaration _forgot_ to use a flag, which is a much more likely bug. So I dunno. If it were more than this one case (well, three, but they are all of the same form) I'd be more worried. -Peff
diff --git a/builtin/interpret-trailers.c b/builtin/interpret-trailers.c index 6aadce6a1e..a5f9adf6b9 100644 --- a/builtin/interpret-trailers.c +++ b/builtin/interpret-trailers.c @@ -24,19 +24,19 @@ static enum trailer_if_exists if_exists; static enum trailer_if_missing if_missing; static int option_parse_where(const struct option *opt, - const char *arg, int unset) + const char *arg, int unset UNUSED) { return trailer_set_where(opt->value, arg); } static int option_parse_if_exists(const struct option *opt, - const char *arg, int unset) + const char *arg, int unset UNUSED) { return trailer_set_if_exists(opt->value, arg); } static int option_parse_if_missing(const struct option *opt, - const char *arg, int unset) + const char *arg, int unset UNUSED) { return trailer_set_if_missing(opt->value, arg); }
There are a few parse-option callbacks that do not look at their "unset" parameters, but also do not set PARSE_OPT_NONEG. At first glance this seems like a bug, as we'd ignore "--no-if-exists", etc. But they do work fine, because when "unset" is true, then "arg" is NULL. And all three functions pass "arg" on to helper functions which do the right thing with the NULL. Note that this shortcut would not be correct if any callback used PARSE_OPT_NOARG (in which case "arg" would be NULL but "unset" would be false). But none of these do. So the code is fine as-is. But we'll want to mark the unused "unset" parameters to quiet -Wunused-parameter. Signed-off-by: Jeff King <peff@peff.net> --- builtin/interpret-trailers.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)