[PATCH] submodule: deprecate --recurse-submodules=""

[Alex Henrie <alexhenrie24@gmail.com>]

The unusual syntax --recurse-submodules="" (that is,
--recurse-submodules with an empty string argument) has been an
undocumented synonym of --recurse-submodules without an argument since
commit 8f0700dd33 (fetch/pull: Add the 'on-demand' value to the
--recurse-submodules option, 2011-03-06). Deprecate that syntax to avoid
confusion with the submodule.recurse config option, where
submodule.recurse="" is equivalent to --no-recurse-submodules.

The same thing was done for --rebase-merges="" in commit 33561f5170
(rebase: deprecate --rebase-merges="", 2023-03-25).

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
---
 submodule-config.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/submodule-config.c b/submodule-config.c
index 6a48fd12f6..8acb42744d 100644
--- a/submodule-config.c
+++ b/submodule-config.c
@@ -332,11 +332,17 @@ int option_fetch_parse_recurse_submodules(const struct option *opt,
 
 	if (unset) {
 		*v = RECURSE_SUBMODULES_OFF;
+	} else if (!arg) {
+		*v = RECURSE_SUBMODULES_ON;
 	} else {
-		if (arg)
-			*v = parse_fetch_recurse_submodules_arg(opt->long_name, arg);
-		else
-			*v = RECURSE_SUBMODULES_ON;
+		if (!*arg) {
+			warning(_("--recurse-submodules with an empty string "
+				  "argument is deprecated and will stop "
+				  "working in a future version of Git. Use "
+				  "--recurse-submodules without an argument "
+				  "instead, which does the same thing."));
+		}
+		*v = parse_fetch_recurse_submodules_arg(opt->long_name, arg);
 	}
 	return 0;
 }
-- 
2.41.0