builtin/apply: move 'state' init into init_apply_state()

When the apply functionality will be libified, the 'struct apply_state'
will be used by different pieces of code.

To properly initialize a 'struct apply_state', let's provide a nice
and easy to use init_apply_state() function.

Let's also provide clear_apply_state() to release memory used by
'struct apply_state' members, so that a 'struct apply_state' instance
can be easily reused without leaking memory.

Note that clear_apply_state() does nothing for now, but it will later.

While at it, let's rename 'prefix_' parameter to 'prefix'.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Reviewed-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/apply.c

@@ -4522,7 +4522,25 @@ static int option_parse_directory(const struct option *opt,
 	return 0;
 }
 
-int cmd_apply(int argc, const char **argv, const char *prefix_)
+static void init_apply_state(struct apply_state *state, const char *prefix)
+{
+	memset(state, 0, sizeof(*state));
+	state->prefix = prefix;
+	state->prefix_length = state->prefix ? strlen(state->prefix) : 0;
+
+	git_apply_config();
+	if (apply_default_whitespace)
+		parse_whitespace_option(apply_default_whitespace);
+	if (apply_default_ignorewhitespace)
+		parse_ignorewhitespace_option(apply_default_ignorewhitespace);
+}
+
+static void clear_apply_state(struct apply_state *state)
+{
+	/* empty for now */
+}
+
+int cmd_apply(int argc, const char **argv, const char *prefix)
 {
 	int i;
 	int errs = 0;
@@ -4603,15 +4621,7 @@ int cmd_apply(int argc, const char **argv, const char *prefix_)
 		OPT_END()
 	};
 
-	memset(&state, 0, sizeof(state));
-	state.prefix = prefix_;
-	state.prefix_length = state.prefix ? strlen(state.prefix) : 0;
-
-	git_apply_config();
-	if (apply_default_whitespace)
-		parse_whitespace_option(apply_default_whitespace);
-	if (apply_default_ignorewhitespace)
-		parse_ignorewhitespace_option(apply_default_ignorewhitespace);
+	init_apply_state(&state, prefix);
 
 	argc = parse_options(argc, argv, state.prefix, builtin_apply_options,
 			apply_usage, 0);
@@ -4695,5 +4705,7 @@ int cmd_apply(int argc, const char **argv, const char *prefix_)
 			die(_("Unable to write new index file"));
 	}
 
+	clear_apply_state(&state);
+
 	return !!errs;
 }