vim-patch:8.1.2214: too much is redrawn when 'cursorline' is set

Problem:    Too much is redrawn when 'cursorline' is set.
Solution:   Don't do a complete redraw. (closes vim/vim#5079)
11a58af66f

src/nvim/change.c

@@ -290,14 +290,21 @@ static void changed_common(linenr_T lnum, colnr_T col, linenr_T lnume,
         set_topline(wp, wp->w_topline);
       }
 
-      // Relative numbering may require updating more.  Cursor line
-      // highlighting probably needs to be updated if it's below the
-      // change (or is using screenline highlighting).
-      if (wp->w_p_rnu
-          || ((wp->w_p_cul && lnum <= wp->w_last_cursorline)
-              || (wp->w_p_culopt_flags & CULOPT_SCRLINE))) {
+      // Relative numbering may require updating more.
+      if (wp->w_p_rnu) {
         redraw_later(wp, SOME_VALID);
       }
+
+      // Cursor line highlighting probably need to be updated with
+      // "VALID" if it's below the change.
+      // If the cursor line is inside the change we need to redraw more.
+      if (wp->w_p_cul) {
+        if (xtra == 0) {
+          redraw_later(wp, VALID);
+        } else if (lnum <= wp->w_last_cursorline) {
+          redraw_later(wp, SOME_VALID);
+        }
+      }
     }
   }
 

src/nvim/normal.c

@@ -1275,25 +1275,19 @@ static void normal_redraw(NormalState *s)
     redrawWinline(curwin, curwin->w_cursor.lnum);
   }
 
-  if (curwin->w_p_cul && curwin->w_p_wrap
-      && (curwin->w_p_culopt_flags & CULOPT_SCRLINE)) {
-    must_redraw = NOT_VALID;
+  // Might need to update for 'cursorline'.
+  // When 'cursorlineopt' is "screenline" need to redraw always.
+  if (curwin->w_p_cul
+      && (curwin->w_last_cursorline != curwin->w_cursor.lnum
+          || (curwin->w_p_culopt_flags & CULOPT_SCRLINE))
+      && !char_avail()) {
+    redraw_later(curwin, VALID);
   }
 
   if (VIsual_active) {
     update_curbuf(INVERTED);  // update inverted part
   } else if (must_redraw) {
-    // Might need some more update for the cursorscreen line.
-    // TODO(vim): can we optimized this?
-    if (curwin->w_p_cul
-        && curwin->w_p_wrap
-        && (curwin->w_p_culopt_flags & CULOPT_SCRLINE)
-        && !char_avail()) {
-      update_screen(VALID);
-    }
-    else {
-      update_screen(0);
-    }
+    update_screen(0);
   } else if (redraw_cmdline || clear_cmdline) {
     showmode();
   }

src/nvim/screen.c

@@ -1371,7 +1371,9 @@ static void win_update(win_T *wp, Providers *providers)
                         // match in fixed position might need redraw
                         // if lines were inserted or deleted
                         || (wp->w_match_head != NULL
-                            && buf->b_mod_xlines != 0)))))) {
+                            && buf->b_mod_xlines != 0)))))
+        || (wp->w_p_cul && (lnum == wp->w_cursor.lnum
+                            || lnum == wp->w_last_cursorline))) {
       if (lnum == mod_top) {
         top_to_mod = false;
       }