vim-patch:9.0.1602: stray character visible if marker on top of double-wide char (#23897)

Problem:    Stray character is visible if 'smoothscroll' marker is displayed
            on top of a double-wide character.
Solution:   When overwriting a double-width character with the 'smoothscroll'
            marker clear the second half. (closes vim/vim#12469)

https://github.com/vim/vim/commit/ecb87dd7d3f7b9291092a7dd8fae1e59b9903252

1 files changed, 11 insertions, 8 deletions

diff --git a/src/nvim/grid.c b/src/nvim/grid.c
index aa542c5a2f..f2ceb2ac24 100644
--- a/src/nvim/grid.c
+++ b/src/nvim/grid.c
@@ -500,8 +500,6 @@ static int grid_char_needs_redraw(ScreenGrid *grid, size_t off_from, size_t off_
 void grid_put_linebuf(ScreenGrid *grid, int row, int coloff, int endcol, int clear_width,
                       int rlflag, win_T *wp, int bg_attr, bool wrap)
 {
-  size_t max_off_from;
-  size_t max_off_to;
   int col = 0;
   bool redraw_next;                         // redraw_this for next character
   bool clear_next = false;
@@ -519,6 +517,7 @@ void grid_put_linebuf(ScreenGrid *grid, int row, int coloff, int endcol, int cle
     endcol = grid->cols;
   }
 
+  const size_t max_off_from = (size_t)grid->cols;
   grid_adjust(&grid, &row, &coloff);
 
   // Safety check. Avoids clang warnings down the call stack.
@@ -529,8 +528,7 @@ void grid_put_linebuf(ScreenGrid *grid, int row, int coloff, int endcol, int cle
 
   size_t off_from = 0;
   size_t off_to = grid->line_offset[row] + (size_t)coloff;
-  max_off_from = linebuf_size;
-  max_off_to = grid->line_offset[row] + (size_t)grid->cols;
+  const size_t max_off_to = grid->line_offset[row] + (size_t)grid->cols;
 
   // Take care of putting "<<<" on the first line for 'smoothscroll'.
   if (topline && wp->w_skipcol > 0
@@ -538,18 +536,23 @@ void grid_put_linebuf(ScreenGrid *grid, int row, int coloff, int endcol, int cle
       && *get_showbreak_value(wp) == NUL
       // do not overwrite the 'listchars' "precedes" text with "<<<"
       && !(wp->w_p_list && wp->w_p_lcs_chars.prec != 0)) {
-    int off = 0;
-    int skip = 0;
+    size_t off = 0;
+    size_t skip = 0;
     if (wp->w_p_nu && wp->w_p_rnu) {
       // do not overwrite the line number, change "123 text" to
       // "123>>>xt".
-      while (skip < wp->w_width_inner && ascii_isdigit(*linebuf_char[off])) {
+      while (skip < max_off_from && ascii_isdigit(*linebuf_char[off])) {
         off++;
         skip++;
       }
     }
 
-    for (int i = 0; i < 3 && i + skip < wp->w_width_inner; i++) {
+    for (size_t i = 0; i < 3 && i + skip < max_off_from; i++) {
+      if (line_off2cells(linebuf_char, off, max_off_from) > 1) {
+        // When the first half of a double-width character is
+        // overwritten, change the second half to a space.
+        schar_from_ascii(linebuf_char[off + 1], ' ');
+      }
       schar_from_ascii(linebuf_char[off], '<');
       linebuf_attr[off] = HL_ATTR(HLF_AT);
       off++;