vim-patch:8.2.5047: CurSearch highlight is often wrong

Problem:    CurSearch highlight is often wrong.
Solution:   Remember the last highlighted position and redraw when needed.

368137aa52

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/change.c

@@ -392,6 +392,10 @@ static void changed_common(buf_T *buf, linenr_T lnum, colnr_T col, linenr_T lnum
         }
       }
     }
+
+    if (wp == curwin && xtra != 0 && search_hl_has_cursor_lnum >= lnum) {
+      search_hl_has_cursor_lnum += xtra;
+    }
   }
 
   // Call update_screen() later, which checks out what needs to be redrawn,

src/nvim/drawscreen.c

@@ -1593,6 +1593,18 @@ static void win_update(win_T *wp)
         }
       }
     }
+
+    if (search_hl_has_cursor_lnum > 0) {
+      // CurSearch was used last time, need to redraw the line with it to
+      // avoid having two matches highlighted with CurSearch.
+      if (mod_top == 0 || mod_top > search_hl_has_cursor_lnum) {
+        mod_top = search_hl_has_cursor_lnum;
+      }
+      if (mod_bot == 0 || mod_bot < search_hl_has_cursor_lnum + 1) {
+        mod_bot = search_hl_has_cursor_lnum + 1;
+      }
+    }
+
     if (mod_top != 0 && hasAnyFolding(wp)) {
       // A change in a line can cause lines above it to become folded or
       // unfolded.  Find the top most buffer line that may be affected.
@@ -1651,6 +1663,7 @@ static void win_update(win_T *wp)
 
   wp->w_redraw_top = 0;  // reset for next time
   wp->w_redraw_bot = 0;
+  search_hl_has_cursor_lnum = 0;
 
   // When only displaying the lines at the top, set top_end.  Used when
   // window has scrolled down for msg_scrolled.

src/nvim/drawscreen.h

@@ -25,7 +25,11 @@ EXTERN bool updating_screen INIT( = false);
 /// must_redraw to be set.
 EXTERN bool redraw_not_allowed INIT( = false);
 
-EXTERN match_T screen_search_hl INIT( = { 0 });  ///< used for 'hlsearch' highlight matching
+/// used for 'hlsearch' highlight matching
+EXTERN match_T screen_search_hl INIT( = { 0 });
+
+/// last lnum where CurSearch was displayed
+EXTERN linenr_T search_hl_has_cursor_lnum INIT( = 0);
 
 #define W_ENDCOL(wp)   ((wp)->w_wincol + (wp)->w_width)
 #define W_ENDROW(wp)   ((wp)->w_winrow + (wp)->w_height)

src/nvim/match.c

@@ -706,6 +706,9 @@ int update_search_hl(win_T *wp, linenr_T lnum, colnr_T col, char **line, match_T
         // group.
         if (shl == search_hl && shl->has_cursor) {
           shl->attr_cur = win_hl_attr(wp, HLF_LC);
+          if (shl->attr_cur != shl->attr) {
+            search_hl_has_cursor_lnum = lnum;
+          }
         } else {
           shl->attr_cur = shl->attr;
         }