builtin/apply: move 'state' check into check_apply_state()

To libify the apply functionality we should provide a function
to check that the values in a 'struct apply_state' instance are
coherent. Let's move the code to do that into a new
check_apply_state() function.

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

@@ -4679,11 +4679,38 @@ static void clear_apply_state(struct apply_state *state)
 	/* &state->fn_table is cleared at the end of apply_patch() */
 }
 
+static void check_apply_state(struct apply_state *state, int force_apply)
+{
+	int is_not_gitdir = !startup_info->have_repository;
+
+	if (state->apply_with_reject && state->threeway)
+		die("--reject and --3way cannot be used together.");
+	if (state->cached && state->threeway)
+		die("--cached and --3way cannot be used together.");
+	if (state->threeway) {
+		if (is_not_gitdir)
+			die(_("--3way outside a repository"));
+		state->check_index = 1;
+	}
+	if (state->apply_with_reject)
+		state->apply = state->apply_verbosely = 1;
+	if (!force_apply && (state->diffstat || state->numstat || state->summary || state->check || state->fake_ancestor))
+		state->apply = 0;
+	if (state->check_index && is_not_gitdir)
+		die(_("--index outside a repository"));
+	if (state->cached) {
+		if (is_not_gitdir)
+			die(_("--cached outside a repository"));
+		state->check_index = 1;
+	}
+	if (state->check_index)
+		state->unsafe_paths = 0;
+}
+
 int cmd_apply(int argc, const char **argv, const char *prefix)
 {
 	int i;
 	int errs = 0;
-	int is_not_gitdir = !startup_info->have_repository;
 	int force_apply = 0;
 	int options = 0;
 	int read_stdin = 1;
@@ -4763,28 +4790,7 @@ int cmd_apply(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, state.prefix, builtin_apply_options,
 			apply_usage, 0);
 
-	if (state.apply_with_reject && state.threeway)
+	check_apply_state(&state, force_apply);
-		die("--reject and --3way cannot be used together.");
-	if (state.cached && state.threeway)
-		die("--cached and --3way cannot be used together.");
-	if (state.threeway) {
-		if (is_not_gitdir)
-			die(_("--3way outside a repository"));
-		state.check_index = 1;
-	}
-	if (state.apply_with_reject)
-		state.apply = state.apply_verbosely = 1;
-	if (!force_apply && (state.diffstat || state.numstat || state.summary || state.check || state.fake_ancestor))
-		state.apply = 0;
-	if (state.check_index && is_not_gitdir)
-		die(_("--index outside a repository"));
-	if (state.cached) {
-		if (is_not_gitdir)
-			die(_("--cached outside a repository"));
-		state.check_index = 1;
-	}
-	if (state.check_index)
-		state.unsafe_paths = 0;
 
 	for (i = 0; i < argc; i++) {
 		const char *arg = argv[i];