fix(mouse): click after eol with conceal and virtual text (#27897)

Problem:  Wrong cursor position when clicking after end of line with
          'virtualedit', conceal and virtual text.
Solution: Always fill linebuf_vcol[] for the columns to clear.

src/nvim/drawline.c

@@ -300,7 +300,6 @@ static void draw_virt_text(win_T *wp, buf_T *buf, int col_off, int *end_col, int
       if (vt->pos == kVPosEndOfLine && do_eol) {
         state->eol_col = col + 1;
       }
-      // TODO(zeertzjq): set values in linebuf_vcol[]
       *end_col = MAX(*end_col, col);
     }
     if (!vt || !(vt->flags & kVTRepeatLinebreak)) {
@@ -2571,6 +2570,10 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
         decor_redraw_eol(wp, &decor_state, &wlv.line_attr, wlv.col + eol_skip);
       }
 
+      for (int i = wlv.col; i < grid->cols; i++) {
+        linebuf_vcol[wlv.off + (i - wlv.col)] = wlv.vcol + (i - wlv.col);
+      }
+
       if (((wp->w_p_cuc
             && wp->w_virtcol >= vcol_hlc(wlv) - eol_hl_off
             && wp->w_virtcol < grid->cols * (ptrdiff_t)(wlv.row - startrow + 1) + start_col
@@ -2596,8 +2599,7 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
 
         while (wlv.col < grid->cols) {
           linebuf_char[wlv.off] = schar_from_ascii(' ');
-          linebuf_vcol[wlv.off] = wlv.vcol;
+
-          wlv.col++;
           advance_color_col(&wlv, vcol_hlc(wlv));
 
           int col_attr = base_attr;
@@ -2616,7 +2618,9 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
           col_attr = hl_combine_attr(col_attr, wlv.line_attr);
 
           linebuf_attr[wlv.off] = col_attr;
+          // linebuf_vcol[] already filled by the for loop above
           wlv.off++;
+          wlv.col++;
 
           if (vcol_hlc(wlv) >= rightmost_vcol) {
             break;
@@ -2857,13 +2861,17 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
 
       int draw_col = wlv.col - wlv.boguscols;
 
+      for (int i = draw_col; i < grid->cols; i++) {
+        linebuf_vcol[wlv.off + (i - draw_col)] = wlv.vcol - 1;
+      }
+
       // Apply 'cursorline' highlight.
       if (wlv.boguscols != 0 && (wlv.line_attr_lowprio != 0 || wlv.line_attr != 0)) {
         int attr = hl_combine_attr(wlv.line_attr_lowprio, wlv.line_attr);
         while (draw_col < grid->cols) {
           linebuf_char[wlv.off] = schar_from_char(' ');
           linebuf_attr[wlv.off] = attr;
-          linebuf_vcol[wlv.off] = wlv.vcol - 1;
+          // linebuf_vcol[] already filled by the for loop above
           wlv.off++;
           draw_col++;
         }

test/functional/ui/mouse_spec.lua

@@ -34,6 +34,7 @@ describe('ui/mouse/input', function()
       [6] = { foreground = Screen.colors.Grey100, background = Screen.colors.Red },
       [7] = { bold = true, foreground = Screen.colors.SeaGreen4 },
       [8] = { foreground = Screen.colors.Brown },
+      [9] = { background = Screen.colors.DarkGrey, foreground = Screen.colors.LightGrey },
     })
     command('set mousemodel=extend')
     feed('itesting<cr>mouse<cr>support and selection<esc>')
@@ -1638,6 +1639,59 @@ describe('ui/mouse/input', function()
     end)
   end)
 
+  it('virtual text does not change cursor placement on concealed line', function()
+    command('%delete')
+    insert('aaaaaaaaaa|hidden|bbbbbbbbbb|hidden|cccccccccc')
+    command('syntax match test /|hidden|/ conceal cchar=X')
+    command('set conceallevel=2 concealcursor=n virtualedit=all')
+    screen:expect([[
+      aaaaaaaaaa{9:X}bbbbbbb       |
+      bbb{9:X}ccccccccc^c           |
+      {0:~                        }|*2
+                               |
+    ]])
+    api.nvim_input_mouse('left', 'press', '', 0, 0, 22)
+    screen:expect([[
+      aaaaaaaaaa{9:X}bbbbbb^b       |
+      bbb{9:X}cccccccccc           |
+      {0:~                        }|*2
+                               |
+    ]])
+    api.nvim_input_mouse('left', 'press', '', 0, 1, 16)
+    screen:expect([[
+      aaaaaaaaaa{9:X}bbbbbbb       |
+      bbb{9:X}cccccccccc  ^         |
+      {0:~                        }|*2
+                               |
+    ]])
+
+    api.nvim_buf_set_extmark(0, api.nvim_create_namespace(''), 0, 0, {
+      virt_text = { { '?', 'ErrorMsg' } },
+      virt_text_pos = 'right_align',
+      virt_text_repeat_linebreak = true,
+    })
+    screen:expect([[
+      aaaaaaaaaa{9:X}bbbbbbb      {6:?}|
+      bbb{9:X}cccccccccc  ^        {6:?}|
+      {0:~                        }|*2
+                               |
+    ]])
+    api.nvim_input_mouse('left', 'press', '', 0, 0, 22)
+    screen:expect([[
+      aaaaaaaaaa{9:X}bbbbbb^b      {6:?}|
+      bbb{9:X}cccccccccc          {6:?}|
+      {0:~                        }|*2
+                               |
+    ]])
+    api.nvim_input_mouse('left', 'press', '', 0, 1, 16)
+    screen:expect([[
+      aaaaaaaaaa{9:X}bbbbbbb      {6:?}|
+      bbb{9:X}cccccccccc  ^        {6:?}|
+      {0:~                        }|*2
+                               |
+    ]])
+  end)
+
   it('getmousepos() works correctly', function()
     local winwidth = api.nvim_get_option_value('winwidth', {})
     -- Set winwidth=1 so that window sizes don't change.