[RFC PATCH] parse-options: disallow double-negations of options starting with no-

[Jacob Keller <jacob.e.keller@intel.com>]

From: Jacob Keller <jacob.keller@gmail.com>

Many options can be negated by prefixing the option with "no-", for
example "--3way" can be prefixed with "--no-3way" to disable it. Since
0f1930c58754 ("parse-options: allow positivation of options
starting, with no-", 2012-02-25) we have also had support to negate
options which start with "no-" by using the positive wording.

This leads to the confusing (and non-documented) case that you can still
prefix options beginning with "no-" by a second "no-" to negate them.
That is, we allow "no-no-hardlinks" to negate the "no-hardlinks" option.

This can be confusing to the user so lets just disallow the
double-negative forms. If the long_name begins with "no-" then we simply
don't allow the regular negation format, and only allow the option to be
negated by the positive form.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
---
I started going about implementing an OPT_NEGBOOL as suggested by Peff,
but realized this might just be simpler, and we already support the
positive format for the negation, so we don't lose expressiveness. We
*might* want to tie this to an option flag instead so that it only kicks
in if the option specifically requests it. Thoughts?

 parse-options.c          | 3 +++
 t/t0040-parse-options.sh | 5 ++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/parse-options.c b/parse-options.c
index a23a1e67f04f..8e024c569f52 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -299,6 +299,9 @@ static int parse_long_opt(struct parse_opt_ctx_t *p, const char *arg,
 				}
 				continue;
 			}
+			/* avoid double-negate on long_name */
+			if (starts_with(long_name, "no-"))
+				continue;
 			flags |= OPT_UNSET;
 			if (!skip_prefix(arg + 3, long_name, &rest)) {
 				/* abbreviated and negated? */
diff --git a/t/t0040-parse-options.sh b/t/t0040-parse-options.sh
index 74d2cd76fe56..abccfa5f265f 100755
--- a/t/t0040-parse-options.sh
+++ b/t/t0040-parse-options.sh
@@ -88,7 +88,6 @@ test_expect_success 'OPT_BOOL() is idempotent #1' 'check boolean: 1 --yes --yes'
 test_expect_success 'OPT_BOOL() is idempotent #2' 'check boolean: 1 -DB'
 
 test_expect_success 'OPT_BOOL() negation #1' 'check boolean: 0 -D --no-yes'
-test_expect_success 'OPT_BOOL() negation #2' 'check boolean: 0 -D --no-no-doubt'
 
 test_expect_success 'OPT_BOOL() no negation #1' 'check_unknown_i18n --fear'
 test_expect_success 'OPT_BOOL() no negation #2' 'check_unknown_i18n --no-no-fear'
@@ -392,4 +391,8 @@ test_expect_success '--no-verbose resets multiple verbose to 0' '
 	test-parse-options --expect="verbose: 0" -v -v -v --no-verbose
 '
 
+test_expect_success 'double negation not accepted' '
+	test_must_fail test-parse-options --expect="boolean: 0" --no-no-doubt
+'
+
 test_done
-- 
2.12.2.882.g942b4cedeff1.dirty