vim-patch:9.1.0137: <Del> in cmdline mode doesn't delete composing chars (#27636)

Problem:  <Del> in cmdline mode doesn't delete composing chars
Solution: Use mb_head_off() and mb_ptr2len() (zeertzjq)

closes: vim/vim#14095

https://github.com/vim/vim/commit/ff2b79d23956263ab0120623c37e0b4498be01db

2 files changed, 15 insertions, 3 deletions

diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index c396bbaae3..44a78711d2 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -1510,10 +1510,8 @@ static int command_line_erase_chars(CommandLineState *s)
   if (s->c == K_DEL && ccline.cmdpos != ccline.cmdlen) {
     ccline.cmdpos++;
   }
-
   if (s->c == K_DEL) {
-    CharBoundsOff bounds = utf_cp_bounds(ccline.cmdbuff, ccline.cmdbuff + ccline.cmdpos);
-    ccline.cmdpos += bounds.begin_off != 0 ? bounds.end_off : 0;
+    ccline.cmdpos += mb_off_next(ccline.cmdbuff, ccline.cmdbuff + ccline.cmdpos);
   }
 
   if (ccline.cmdpos > 0) {
diff --git a/src/nvim/mbyte.c b/src/nvim/mbyte.c
index cf206aa68b..c7a56209e4 100644
--- a/src/nvim/mbyte.c
+++ b/src/nvim/mbyte.c
@@ -1884,6 +1884,20 @@ void mb_copy_char(const char **const fp, char **const tp)
   *fp += l;
 }
 
+/// Return the offset from "p" to the first byte of a character.  When "p" is
+/// at the start of a character 0 is returned, otherwise the offset to the next
+/// character.  Can start anywhere in a stream of bytes.
+int mb_off_next(const char *base, const char *p)
+{
+  int head_off = utf_head_off(base, p);
+
+  if (head_off == 0) {
+    return 0;
+  }
+
+  return utfc_ptr2len(p - head_off) - head_off;
+}
+
 /// Returns the offset in bytes from "p_in" to the first and one-past-end bytes
 /// of the codepoint it points to.
 /// "p_in" can point anywhere in a stream of bytes.