ls-tree: simplify prefix handling

git ls-tree has two prefixes: The one handed to cmd_ls_tree(), i.e. the
current subdirectory in the repository (if any) and the "display" prefix
used by the show_tree_*() functions.  The option --full-name clears the
last one, i.e. it shows full paths, and --full-tree clears both, i.e. it
acts as if the command was started in the root of the repository.

The show_tree_*() functions use the ls_tree_options members chomp_prefix
and ls_tree_prefix to determine their prefix values.  Calculate it once
in cmd_ls_tree() instead, once the main prefix value is finalized.

This allows chomp_prefix to become a local variable.  Stop using
strlen(3) to determine its initial value -- we only care whether we got
a non-empty string, not precisely how long it is.

Rename ls_tree_prefix to prefix to demonstrate that we converted all
users and because the ls_tree_ part is no longer necessary since
030a3d5d9e (ls-tree: use a "struct options", 2023-01-12) turned it from
a global variable to a struct member.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/ls-tree.c

@@ -50,8 +50,7 @@ struct ls_tree_options {
 		LS_SHOW_TREES = 1 << 2,
 	} ls_options;
 	struct pathspec pathspec;
-	int chomp_prefix;
-	const char *ls_tree_prefix;
+	const char *prefix;
 	const char *format;
 };
 
@@ -128,8 +127,7 @@ static int show_tree_fmt(const struct object_id *oid, struct strbuf *base,
 			strbuf_add_unique_abbrev(&sb, oid, options->abbrev);
 		else if (skip_prefix(format, "(path)", &format)) {
 			const char *name;
-			const char *prefix = options->chomp_prefix ?
-					     options->ls_tree_prefix : NULL;
+			const char *prefix = options->prefix;
 			struct strbuf sbuf = STRBUF_INIT;
 			size_t baselen = base->len;
 
@@ -173,7 +171,7 @@ static void show_tree_common_default_long(struct ls_tree_options *options,
 					  const char *pathname,
 					  const size_t baselen)
 {
-	const char *prefix = options->chomp_prefix ? options->ls_tree_prefix : NULL;
+	const char *prefix = options->prefix;
 
 	strbuf_addstr(base, pathname);
 
@@ -258,7 +256,7 @@ static int show_tree_name_only(const struct object_id *oid, struct strbuf *base,
 	if (early >= 0)
 		return early;
 
-	prefix = options->chomp_prefix ? options->ls_tree_prefix : NULL;
+	prefix = options->prefix;
 	strbuf_addstr(base, pathname);
 	if (options->null_termination) {
 		struct strbuf sb = STRBUF_INIT;
@@ -345,6 +343,7 @@ int cmd_ls_tree(int argc, const char **argv, const char *prefix)
 	struct object_id oid;
 	struct tree *tree;
 	int i, full_tree = 0;
+	int chomp_prefix = prefix && *prefix;
 	read_tree_fn_t fn = NULL;
 	enum ls_tree_cmdmode cmdmode = MODE_DEFAULT;
 	int null_termination = 0;
@@ -366,7 +365,7 @@ int cmd_ls_tree(int argc, const char **argv, const char *prefix)
 			    MODE_NAME_STATUS),
 		OPT_CMDMODE(0, "object-only", &cmdmode, N_("list only objects"),
 			    MODE_OBJECT_ONLY),
-		OPT_SET_INT(0, "full-name", &options.chomp_prefix,
+		OPT_SET_INT(0, "full-name", &chomp_prefix,
 			    N_("use full path names"), 0),
 		OPT_BOOL(0, "full-tree", &full_tree,
 			 N_("list entire tree; not just current directory "
@@ -381,18 +380,15 @@ int cmd_ls_tree(int argc, const char **argv, const char *prefix)
 	int ret;
 
 	git_config(git_default_config, NULL);
-	options.ls_tree_prefix = prefix;
-	if (prefix)
-		options.chomp_prefix = strlen(prefix);
 
 	argc = parse_options(argc, argv, prefix, ls_tree_options,
 			     ls_tree_usage, 0);
 	options.null_termination = null_termination;
 
-	if (full_tree) {
-		options.ls_tree_prefix = prefix = NULL;
-		options.chomp_prefix = 0;
-	}
+	if (full_tree)
+		prefix = NULL;
+	options.prefix = chomp_prefix ? prefix : NULL;
+
 	/*
 	 * We wanted to detect conflicts between --name-only and
 	 * --name-status, but once we're done with that subsequent