help: fix leaking return value from `help_unknown_cmd()`

While `help_unknown_cmd()` would usually die on an unknown command, it
instead returns an autocorrected command when "help.autocorrect" is set.
But while the function is declared to return a string constant, it
actually returns an allocated string in that case. Callers thus aren't
aware that they have to free the string, leading to a memory leak.

Fix the function return type to be non-constant and free the returned
value at its only callsite.

Note that we cannot simply take ownership of `main_cmds.names[0]->name`
and then eventually free it. This is because the `struct cmdname` is
using a flex array to allocate the name, so the name pointer points into
the middle of the structure and thus cannot be freed.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 3 insertions, 4 deletions

diff --git a/help.c b/help.c
index 8b56cd6e25..8a830ba35c 100644
--- a/help.c
+++ b/help.c
@@ -612,7 +612,7 @@ static const char bad_interpreter_advice[] =
 	N_("'%s' appears to be a git command, but we were not\n"
 	"able to execute it. Maybe git-%s is broken?");
 
-const char *help_unknown_cmd(const char *cmd)
+char *help_unknown_cmd(const char *cmd)
 {
 	struct help_unknown_cmd_config cfg = { 0 };
 	int i, n, best_similarity = 0;
@@ -695,9 +695,8 @@ const char *help_unknown_cmd(const char *cmd)
 			; /* still counting */
 	}
 	if (cfg.autocorrect && n == 1 && SIMILAR_ENOUGH(best_similarity)) {
-		const char *assumed = main_cmds.names[0]->name;
-		main_cmds.names[0] = NULL;
-		cmdnames_release(&main_cmds);
+		char *assumed = xstrdup(main_cmds.names[0]->name);
+
 		fprintf_ln(stderr,
 			   _("WARNING: You called a Git command named '%s', "
 			     "which does not exist."),