checkout: pass "struct checkout_opts *" as const pointer

This struct contains various switches to system and it feels somewhat
safer to have the compiler reassure us that nowhere else changes it.

One field that is changed, writeout_error, is split out and passed as
another argument.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pclouds

builtin/checkout.c

@@ -33,7 +33,6 @@ struct checkout_opts {
 	int force;
 	int force_detach;
 	int writeout_stage;
-	int writeout_error;
 	int overwrite_ignore;
 
 	/* not set by parse_options */
@@ -216,7 +215,7 @@ static int checkout_merged(int pos, struct checkout *state)
 }
 
 static int checkout_paths(struct tree *source_tree, const char **pathspec,
-			  const char *prefix, struct checkout_opts *opts)
+			  const char *prefix, const struct checkout_opts *opts)
 {
 	int pos;
 	struct checkout state;
@@ -309,7 +308,8 @@ static int checkout_paths(struct tree *source_tree, const char **pathspec,
 	return errs;
 }
 
-static void show_local_changes(struct object *head, struct diff_options *opts)
+static void show_local_changes(struct object *head,
+			       const struct diff_options *opts)
 {
 	struct rev_info rev;
 	/* I think we want full paths, even if we're in a subdirectory. */
@@ -331,7 +331,8 @@ static void describe_detached_head(const char *msg, struct commit *commit)
 	strbuf_release(&sb);
 }
 
-static int reset_tree(struct tree *tree, struct checkout_opts *o, int worktree)
+static int reset_tree(struct tree *tree, const struct checkout_opts *o,
+		      int worktree, int *writeout_error)
 {
 	struct unpack_trees_options opts;
 	struct tree_desc tree_desc;
@@ -350,7 +351,7 @@ static int reset_tree(struct tree *tree, struct checkout_opts *o, int worktree)
 	init_tree_desc(&tree_desc, tree->buffer, tree->size);
 	switch (unpack_trees(1, &tree_desc, &opts)) {
 	case -2:
-		o->writeout_error = 1;
+		*writeout_error = 1;
 		/*
 		 * We return 0 nevertheless, as the index is all right
 		 * and more importantly we have made best efforts to
@@ -381,8 +382,10 @@ static void setup_branch_path(struct branch_info *branch)
 	branch->path = strbuf_detach(&buf, NULL);
 }
 
-static int merge_working_tree(struct checkout_opts *opts,
-			      struct branch_info *old, struct branch_info *new)
+static int merge_working_tree(const struct checkout_opts *opts,
+			      struct branch_info *old,
+			      struct branch_info *new,
+			      int *writeout_error)
 {
 	int ret;
 	struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
@@ -393,7 +396,7 @@ static int merge_working_tree(struct checkout_opts *opts,
 
 	resolve_undo_clear();
 	if (opts->force) {
-		ret = reset_tree(new->commit->tree, opts, 1);
+		ret = reset_tree(new->commit->tree, opts, 1, writeout_error);
 		if (ret)
 			return ret;
 	} else {
@@ -479,15 +482,17 @@ static int merge_working_tree(struct checkout_opts *opts,
 			o.verbosity = 0;
 			work = write_tree_from_memory(&o);
 
-			ret = reset_tree(new->commit->tree, opts, 1);
+			ret = reset_tree(new->commit->tree, opts, 1,
+					 writeout_error);
 			if (ret)
 				return ret;
 			o.ancestor = old->name;
 			o.branch1 = new->name;
 			o.branch2 = "local";
 			merge_trees(&o, new->commit->tree, work,
 				old->commit->tree, &result);
-			ret = reset_tree(new->commit->tree, opts, 0);
+			ret = reset_tree(new->commit->tree, opts, 0,
+					 writeout_error);
 			if (ret)
 				return ret;
 		}
@@ -514,7 +519,7 @@ static void report_tracking(struct branch_info *new)
 	strbuf_release(&sb);
 }
 
-static void update_refs_for_switch(struct checkout_opts *opts,
+static void update_refs_for_switch(const struct checkout_opts *opts,
 				   struct branch_info *old,
 				   struct branch_info *new)
 {
@@ -701,13 +706,13 @@ static void orphaned_commit_warning(struct commit *old, struct commit *new)
 	free(refs.objects);
 }
 
-static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
+static int switch_branches(const struct checkout_opts *opts, struct branch_info *new)
 {
 	int ret = 0;
 	struct branch_info old;
 	void *path_to_free;
 	unsigned char rev[20];
-	int flag;
+	int flag, writeout_error = 0;
 	memset(&old, 0, sizeof(old));
 	old.path = path_to_free = resolve_refdup("HEAD", rev, 0, &flag);
 	old.commit = lookup_commit_reference_gently(rev, 1);
@@ -725,7 +730,7 @@ static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
 		parse_commit(new->commit);
 	}
 
-	ret = merge_working_tree(opts, &old, new);
+	ret = merge_working_tree(opts, &old, new, &writeout_error);
 	if (ret) {
 		free(path_to_free);
 		return ret;
@@ -738,7 +743,7 @@ static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
 
 	ret = post_checkout_hook(old.commit, new->commit, 1);
 	free(path_to_free);
-	return ret || opts->writeout_error;
+	return ret || writeout_error;
 }
 
 static int git_checkout_config(const char *var, const char *value, void *cb)
@@ -910,7 +915,7 @@ static int parse_branchname_arg(int argc, const char **argv,
 	return argcount;
 }
 
-static int switch_unborn_to_new_branch(struct checkout_opts *opts)
+static int switch_unborn_to_new_branch(const struct checkout_opts *opts)
 {
 	int status;
 	struct strbuf branch_ref = STRBUF_INIT;