parse-options: allow positivation of options starting, with no-

Long options can be negated by adding no- right after the leading
two dashes. This is useful e.g. to override options set by aliases.

For options that are defined to start with no- already, this looks
a bit funny. Allow such options to also be negated by removing the
prefix.

The following thirteen options are affected:

	apply          --no-add
	bisect--helper --no-checkout
	checkout-index --no-create
	clone          --no-checkout --no-hardlinks
	commit         --no-verify   --no-post-rewrite
	format-patch   --no-binary
	hash-object    --no-filters
	read-tree      --no-sparse-checkout
	revert         --no-commit
	show-branch    --no-name
	update-ref     --no-deref

The following five are NOT affected because they are defined with
PARSE_OPT_NONEG or the non-negated version is defined as well:

	branch       --no-merged
	format-patch --no-stat             --no-numbered
	update-index --no-assume-unchanged --no-skip-worktree

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 20 insertions, 12 deletions

diff --git a/Documentation/technical/api-parse-options.txt b/Documentation/technical/api-parse-options.txt
index 4b92514f60..2527b7e8d7 100644
--- a/Documentation/technical/api-parse-options.txt
+++ b/Documentation/technical/api-parse-options.txt
@@ -39,7 +39,8 @@ The parse-options API allows:
 * Short options may be bundled, e.g. `-a -b` can be specified as `-ab`.
 
 * Boolean long options can be 'negated' (or 'unset') by prepending
-  `no-`, e.g. `\--no-abbrev` instead of `\--abbrev`.
+  `no-`, e.g. `\--no-abbrev` instead of `\--abbrev`. Conversely,
+  options that begin with `no-` can be 'negated' by removing it.
 
 * Options and non-option arguments can clearly be separated using the `\--`
   option, e.g. `-a -b \--option \-- \--this-is-a-file` indicates that
diff --git a/parse-options.c b/parse-options.c
index f0098eb8ea..8906841665 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -193,13 +193,14 @@ static int parse_long_opt(struct parse_opt_ctx_t *p, const char *arg,
 		arg_end = arg + strlen(arg);
 
 	for (; options->type != OPTION_END; options++) {
-		const char *rest;
-		int flags = 0;
+		const char *rest, *long_name = options->long_name;
+		int flags = 0, opt_flags = 0;
 
-		if (!options->long_name)
+		if (!long_name)
 			continue;
 
-		rest = skip_prefix(arg, options->long_name);
+again:
+		rest = skip_prefix(arg, long_name);
 		if (options->type == OPTION_ARGUMENT) {
 			if (!rest)
 				continue;
@@ -212,7 +213,7 @@ static int parse_long_opt(struct parse_opt_ctx_t *p, const char *arg,
 		}
 		if (!rest) {
 			/* abbreviated? */
-			if (!strncmp(options->long_name, arg, arg_end - arg)) {
+			if (!strncmp(long_name, arg, arg_end - arg)) {
 is_abbreviated:
 				if (abbrev_option) {
 					/*
@@ -227,7 +228,7 @@ is_abbreviated:
 				if (!(flags & OPT_UNSET) && *arg_end)
 					p->opt = arg_end + 1;
 				abbrev_option = options;
-				abbrev_flags = flags;
+				abbrev_flags = flags ^ opt_flags;
 				continue;
 			}
 			/* negation allowed? */
@@ -239,12 +240,18 @@ is_abbreviated:
 				goto is_abbreviated;
 			}
 			/* negated? */
-			if (strncmp(arg, "no-", 3))
+			if (prefixcmp(arg, "no-")) {
+				if (!prefixcmp(long_name, "no-")) {
+					long_name += 3;
+					opt_flags |= OPT_UNSET;
+					goto again;
+				}
 				continue;
+			}
 			flags |= OPT_UNSET;
-			rest = skip_prefix(arg + 3, options->long_name);
+			rest = skip_prefix(arg + 3, long_name);
 			/* abbreviated and negated? */
-			if (!rest && !prefixcmp(options->long_name, arg + 3))
+			if (!rest && !prefixcmp(long_name, arg + 3))
 				goto is_abbreviated;
 			if (!rest)
 				continue;
@@ -254,7 +261,7 @@ is_abbreviated:
 				continue;
 			p->opt = rest + 1;
 		}
-		return get_value(p, options, flags);
+		return get_value(p, options, flags ^ opt_flags);
 	}
 
 	if (ambiguous_option)
diff --git a/t/t0040-parse-options.sh b/t/t0040-parse-options.sh
index ca25e588ca..a44bcb9b39 100755
--- a/t/t0040-parse-options.sh
+++ b/t/t0040-parse-options.sh
@@ -107,7 +107,7 @@ test_expect_success 'OPT_BOOL() negation #2' 'check boolean: 0 -D --no-no-doubt'
 test_expect_success 'OPT_BOOL() no negation #1' 'check_unknown --fear'
 test_expect_success 'OPT_BOOL() no negation #2' 'check_unknown --no-no-fear'
 
-test_expect_failure 'OPT_BOOL() positivation' 'check boolean: 0 -D --doubt'
+test_expect_success 'OPT_BOOL() positivation' 'check boolean: 0 -D --doubt'
 
 cat > expect << EOF
 boolean: 2