Keep `MRB_STR_ASCII` flag in some methods of `String`

include/mruby/string.h

@@ -107,7 +107,6 @@ MRB_API mrb_int mrb_str_strlen(mrb_state*, struct RString*);
 #define MRB_STR_EMBED_LEN_SHIFT 6
 
 void mrb_gc_free_str(mrb_state*, struct RString*);
-MRB_API void mrb_str_modify(mrb_state*, struct RString*);
 
 /*
  * Finds the index of a substring in a string
@@ -454,6 +453,14 @@ mrb_value mrb_str_inspect(mrb_state *mrb, mrb_value str);
 
 mrb_bool mrb_str_beg_len(mrb_int str_len, mrb_int *begp, mrb_int *lenp);
 mrb_value mrb_str_byte_subseq(mrb_state *mrb, mrb_value str, mrb_int beg, mrb_int len);
+void mrb_str_modify_keep_ascii(mrb_state *mrb, struct RString *s);
+
+MRB_INLINE void
+mrb_str_modify(mrb_state *mrb, struct RString *s)
+{
+  mrb_str_modify_keep_ascii(mrb, s);
+  RSTR_UNSET_ASCII_FLAG(s);
+}
 
 #ifdef MRB_UTF8_STRING
 mrb_int mrb_utf8_len(const char *str, mrb_int byte_len);

src/string.c

@@ -706,11 +706,10 @@ mrb_locale_from_utf8(const char *utf8, int len)
 }
 #endif
 
-MRB_API void
-mrb_str_modify(mrb_state *mrb, struct RString *s)
+void
+mrb_str_modify_keep_ascii(mrb_state *mrb, struct RString *s)
 {
   mrb_check_frozen(mrb, s);
-  RSTR_UNSET_ASCII_FLAG(s);
   if (RSTR_SHARED_P(s)) {
     mrb_shared_string *shared = s->as.heap.aux.shared;
 
@@ -1339,7 +1338,7 @@ mrb_str_capitalize_bang(mrb_state *mrb, mrb_value str)
   mrb_bool modify = FALSE;
   struct RString *s = mrb_str_ptr(str);
 
-  mrb_str_modify(mrb, s);
+  mrb_str_modify_keep_ascii(mrb, s);
   if (RSTR_LEN(s) == 0 || !RSTR_PTR(s)) return mrb_nil_value();
   p = RSTR_PTR(s); pend = RSTR_PTR(s) + RSTR_LEN(s);
   if (ISLOWER(*p)) {
@@ -1398,7 +1397,7 @@ mrb_str_chomp_bang(mrb_state *mrb, mrb_value str)
   struct RString *s = mrb_str_ptr(str);
 
   argc = mrb_get_args(mrb, "|S", &rs);
-  mrb_str_modify(mrb, s);
+  mrb_str_modify_keep_ascii(mrb, s);
   len = RSTR_LEN(s);
   if (argc == 0) {
     if (len == 0) return mrb_nil_value();
@@ -1497,7 +1496,7 @@ mrb_str_chop_bang(mrb_state *mrb, mrb_value str)
 {
   struct RString *s = mrb_str_ptr(str);
 
-  mrb_str_modify(mrb, s);
+  mrb_str_modify_keep_ascii(mrb, s);
   if (RSTR_LEN(s) > 0) {
     mrb_int len;
 #ifdef MRB_UTF8_STRING
@@ -1566,7 +1565,7 @@ mrb_str_downcase_bang(mrb_state *mrb, mrb_value str)
   mrb_bool modify = FALSE;
   struct RString *s = mrb_str_ptr(str);
 
-  mrb_str_modify(mrb, s);
+  mrb_str_modify_keep_ascii(mrb, s);
   p = RSTR_PTR(s);
   pend = RSTR_PTR(s) + RSTR_LEN(s);
   while (p < pend) {
@@ -2536,7 +2535,7 @@ mrb_str_upcase_bang(mrb_state *mrb, mrb_value str)
   char *p, *pend;
   mrb_bool modify = FALSE;
 
-  mrb_str_modify(mrb, s);
+  mrb_str_modify_keep_ascii(mrb, s);
   p = RSTRING_PTR(str);
   pend = RSTRING_END(str);
   while (p < pend) {