assert NOARG/NONEG behavior of parse-options callbacks

When we define a parse-options callback, the flags we put in the option
struct must match what the callback expects. For example, a callback
which does not handle the "unset" parameter should only be used with
PARSE_OPT_NONEG. But since the callback and the option struct are not
defined next to each other, it's easy to get this wrong (as earlier
patches in this series show).

Fortunately, the compiler can help us here: compiling with
-Wunused-parameters can show us which callbacks ignore their "unset"
parameters (and likewise, ones that ignore "arg" expect to be triggered
with PARSE_OPT_NOARG).

But after we've inspected a callback and determined that all of its
callers use the right flags, what do we do next? We'd like to silence
the compiler warning, but do so in a way that will catch any wrong calls
in the future.

We can do that by actually checking those variables and asserting that
they match our expectations. Because this is such a common pattern,
we'll introduce some helper macros. The resulting messages aren't
as descriptive as we could make them, but the file/line information from
BUG() is enough to identify the problem (and anyway, the point is that
these should never be seen).

Each of the annotated callbacks in this patch triggers
-Wunused-parameters, and was manually inspected to make sure all callers
use the correct options (so none of these BUGs should be triggerable).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/parse-options-cb.c b/parse-options-cb.c
index 6a61166..8c9edce 100644
--- a/parse-options-cb.c
+++ b/parse-options-cb.c
@@ -58,6 +58,8 @@ int parse_opt_verbosity_cb(const struct option *opt, const char *arg,
 {
 	int *target = opt->value;
 
+	BUG_ON_OPT_ARG(arg);
+
 	if (unset)
 		/* --no-quiet, --no-verbose */
 		*target = 0;
@@ -80,6 +82,8 @@ int parse_opt_commits(const struct option *opt, const char *arg, int unset)
 	struct object_id oid;
 	struct commit *commit;
 
+	BUG_ON_OPT_NEG(unset);
+
 	if (!arg)
 		return -1;
 	if (get_oid(arg, &oid))
@@ -110,6 +114,9 @@ int parse_opt_object_name(const struct option *opt, const char *arg, int unset)
 int parse_opt_tertiary(const struct option *opt, const char *arg, int unset)
 {
 	int *target = opt->value;
+
+	BUG_ON_OPT_ARG(arg);
+
 	*target = unset ? 2 : 1;
 	return 0;
 }