find_hook: keep our own static buffer

The find_hook function returns the results of git_path,
which is a static buffer shared by other path-related calls.
Returning such a buffer is slightly dangerous, because it
can be overwritten by seemingly unrelated functions.

Let's at least keep our _own_ static buffer, so you can
only get in trouble by calling find_hook in quick
succession, which is less likely to happen and more obvious
to notice.

While we're at it, let's add some documentation of the
function's limitations.

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

run-command.c

@@ -797,11 +797,13 @@ int finish_async(struct async *async)
 
 const char *find_hook(const char *name)
 {
-	const char *path = git_path("hooks/%s", name);
-	if (access(path, X_OK) < 0)
-		path = NULL;
+	static struct strbuf path = STRBUF_INIT;
 
-	return path;
+	strbuf_reset(&path);
+	strbuf_git_path(&path, "hooks/%s", name);
+	if (access(path.buf, X_OK) < 0)
+		return NULL;
+	return path.buf;
 }
 
 int run_hook_ve(const char *const *env, const char *name, va_list args)

run-command.h

@@ -52,6 +52,11 @@ int start_command(struct child_process *);
 int finish_command(struct child_process *);
 int run_command(struct child_process *);
 
+/*
+ * Returns the path to the hook file, or NULL if the hook is missing
+ * or disabled. Note that this points to static storage that will be
+ * overwritten by further calls to find_hook and run_hook_*.
+ */
 extern const char *find_hook(const char *name);
 LAST_ARG_MUST_BE_NULL
 extern int run_hook_le(const char *const *env, const char *name, ...);