vim-patch:8.2.4724: current instance of last search pattern not easily spotted

Problem:    Current instance of last search pattern not easily spotted.
Solution:   Add CurSearch highlighting. (closes vim/vim#10133)

a43993897a

Some code is superseded by later patches that are already ported.

Co-authored-by: LemonBoy <thatlemon@gmail.com>

runtime/doc/news.txt

@@ -47,6 +47,8 @@ EDITOR
 
 • The order in which signs are placed was changed. Higher priority signs will
   now appear left of lower priority signs.
+• |hl-CurSearch| now behaves the same as Vim and no longer updates on every
+  cursor movement.
 
 EVENTS
 

runtime/doc/syntax.txt

@@ -4969,8 +4969,9 @@ ColorColumn	Used for the columns set with 'colorcolumn'.
 Conceal		Placeholder characters substituted for concealed
 		text (see 'conceallevel').
 							*hl-CurSearch*
-CurSearch	Used for highlighting a search pattern under the cursor
-		(see 'hlsearch').
+CurSearch	Current match for the last search pattern (see 'hlsearch').
+		Note: This is correct after a search, but may get outdated if
+		changes are made or the screen is redrawn.
 						*hl-Cursor* *hl-lCursor*
 Cursor		Character under the cursor.
 lCursor		Character under the cursor when |language-mapping|

runtime/doc/vim_diff.txt

@@ -539,8 +539,6 @@ Functions:
 Highlight groups:
 - |hl-ColorColumn|, |hl-CursorColumn| are lower priority than most other
   groups
-- |hl-CurSearch| highlights match under cursor instead of last match found
-  using |n| or |N|
 - |hl-CursorLine| is low-priority unless foreground color is set
 - |hl-VertSplit| superseded by |hl-WinSeparator|
 - Highlight groups names are allowed to contain `@` characters.

src/nvim/move.c

@@ -153,7 +153,6 @@ static void redraw_for_cursorline(win_T *wp)
 /// Redraw when w_virtcol changes and
 /// - 'cursorcolumn' is set, or
 /// - 'cursorlineopt' contains "screenline", or
-/// - "CurSearch" highlight is in use, or
 /// - 'concealcursor' is active, or
 /// - Visual mode is active.
 static void redraw_for_cursorcolumn(win_T *wp)
@@ -173,10 +172,8 @@ static void redraw_for_cursorcolumn(win_T *wp)
     return;
   }
 
-  if (wp->w_p_cuc
-      || (win_hl_attr(wp, HLF_LC) != win_hl_attr(wp, HLF_L) && using_hlsearch())) {
-    // When 'cursorcolumn' is set or "CurSearch" is in use
-    // need to redraw with UPD_SOME_VALID.
+  if (wp->w_p_cuc) {
+    // When 'cursorcolumn' is set need to redraw with UPD_SOME_VALID.
     redraw_later(wp, UPD_SOME_VALID);
   } else if (wp->w_p_cul && (wp->w_p_culopt_flags & CULOPT_SCRLINE)) {
     // When 'cursorlineopt' contains "screenline" need to redraw with UPD_VALID.

src/nvim/normal.c

@@ -3973,6 +3973,12 @@ static void nv_next(cmdarg_T *cap)
     normal_search(cap, 0, NULL, 0, SEARCH_MARK | cap->arg, NULL);
     cap->count1 -= 1;
   }
+
+  // Redraw the window to refresh the highlighted matches.
+  if (i > 0 && p_hls && !no_hlsearch
+      && win_hl_attr(curwin, HLF_LC) != win_hl_attr(curwin, HLF_L)) {
+    redraw_later(curwin, UPD_SOME_VALID);
+  }
 }
 
 /// Search for "pat" in direction "dir" ('/' or '?', 0 for repeat).
@@ -3984,6 +3990,7 @@ static void nv_next(cmdarg_T *cap)
 static int normal_search(cmdarg_T *cap, int dir, char *pat, size_t patlen, int opt, int *wrapped)
 {
   searchit_arg_T sia;
+  pos_T const prev_cursor = curwin->w_cursor;
 
   cap->oap->motion_type = kMTCharWise;
   cap->oap->inclusive = false;
@@ -4007,6 +4014,11 @@ static int normal_search(cmdarg_T *cap, int dir, char *pat, size_t patlen, int o
       foldOpenCursor();
     }
   }
+  // Redraw the window to refresh the highlighted matches.
+  if (!equalpos(curwin->w_cursor, prev_cursor) && p_hls && !no_hlsearch
+      && win_hl_attr(curwin, HLF_LC) != win_hl_attr(curwin, HLF_L)) {
+    redraw_later(curwin, UPD_SOME_VALID);
+  }
 
   // "/$" will put the cursor after the end of the line, may need to
   // correct that here

src/nvim/search.c

@@ -4322,9 +4322,3 @@ bool search_was_last_used(void)
 {
   return last_idx == 0;
 }
-
-/// @return  true if 'hlsearch' highlight is currently in use.
-bool using_hlsearch(void)
-{
-  return spats[last_idx].pat != NULL && p_hls && !no_hlsearch;
-}