fix(drawline): don't draw beyond end of window (#29035)

src/nvim/drawline.c

@@ -1596,6 +1596,10 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
         // hide virt_text on text hidden by 'nowrap' or 'smoothscroll'
         decor_redraw_col(wp, (colnr_T)(ptr - line) - 1, wlv.off, true, &decor_state);
       }
+      if (wlv.col >= grid->cols) {
+        wlv.col = wlv.off = grid->cols;
+        goto end_check;
+      }
     }
 
     if (cul_screenline && wlv.filler_todo <= 0
@@ -2650,13 +2654,6 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
         conceal_cursor_used = conceal_cursor_line(curwin);
       }
 
-      // When the window is too narrow draw all "@" lines.
-      if (leftcols_width >= wp->w_grid.cols && is_wrapped) {
-        win_draw_end(wp, schar_from_ascii('@'), true, wlv.row, wp->w_grid.rows, HLF_AT);
-        set_empty_rows(wp, wlv.row);
-        wlv.row = endrow;
-      }
-
       break;
     }
 
@@ -2844,10 +2841,12 @@ int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, int col_rows, s
       }
     }
 
+end_check:
     // At end of screen line and there is more to come: Display the line
     // so far.  If there is no more to display it is caught above.
     if (wlv.col >= grid->cols && (!has_foldtext || virt_line_offset >= 0)
-        && (*ptr != NUL
+        && (wlv.col <= leftcols_width
+            || *ptr != NUL
             || wlv.filler_todo > 0
             || (wp->w_p_list && wp->w_p_lcs_chars.eol != NUL && lcs_eol_todo)
             || (wlv.n_extra != 0 && (wlv.sc_extra != NUL || *wlv.p_extra != NUL))

test/functional/ui/screen_basic_spec.lua

@@ -4,6 +4,7 @@ local Screen = require('test.functional.ui.screen')
 
 local spawn, set_session, clear = n.spawn, n.set_session, n.clear
 local feed, command = n.feed, n.command
+local exec = n.exec
 local insert = n.insert
 local eq = t.eq
 local fn, api = n.fn, n.api
@@ -819,3 +820,39 @@ it("showcmd doesn't cause empty grid_line with redrawdebug=compositor #22593", f
   ]],
   }
 end)
+
+it("scrolling in narrow window doesn't draw over separator #29033", function()
+  clear()
+  local screen = Screen.new(60, 8)
+  screen:attach()
+  feed('100Oa<Esc>gg')
+  exec([[
+    set number nowrap
+    vsplit
+    set scrollbind
+    wincmd l
+    set scrollbind
+    wincmd |
+  ]])
+  screen:expect([[
+    {8: }│{8:  1 }^a                                                     |
+    {8: }│{8:  2 }a                                                     |
+    {8: }│{8:  3 }a                                                     |
+    {8: }│{8:  4 }a                                                     |
+    {8: }│{8:  5 }a                                                     |
+    {8: }│{8:  6 }a                                                     |
+    {2:< }{3:[No Name] [+]                                             }|
+                                                                |
+  ]])
+  feed('<C-F>')
+  screen:expect([[
+    {8: }│{8:  5 }^a                                                     |
+    {8: }│{8:  6 }a                                                     |
+    {8: }│{8:  7 }a                                                     |
+    {8: }│{8:  8 }a                                                     |
+    {8: }│{8:  9 }a                                                     |
+    {8: }│{8: 10 }a                                                     |
+    {2:< }{3:[No Name] [+]                                             }|
+                                                                |
+  ]])
+end)