display: unify cursorline and concealcursor redraw logic

There is various places where 'conceallevel' and 'concealcursor'
necessitates additional redraws. This tries to separate the different
cases and handle each accordingly:

  - Share code with 'cursorline' for the common case: vertical move of
    cursor within the same window (concealcursor not active)
  - Improve the logic for managing 'concealcursor' and switching modes:
    test for the case where the new mode behaves differently from the
    last one.
  - Clarify the special case for horizontal movement within a line when
    'concealcursor' is active, now there is an if-statement only for this
     and not hidden in larger check mostly for the first point.
  - Keep the special case for moving between windows as is.

6 files changed, 36 insertions, 75 deletions

diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 257a6ef112..bb3c0ec196 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -306,10 +306,6 @@ static void insert_enter(InsertState *s)
     }
   }
 
-  // Check if the cursor line needs redrawing before changing State. If
-  // 'concealcursor' is "n" it needs to be redrawn without concealing.
-  conceal_check_cursor_line();
-
   // When doing a paste with the middle mouse button, Insstart is set to
   // where the paste started.
   if (where_paste_started.lnum != 0) {
@@ -1381,9 +1377,7 @@ ins_redraw (
     int ready                   /* not busy with something */
 )
 {
-  linenr_T conceal_old_cursor_line = 0;
-  linenr_T conceal_new_cursor_line = 0;
-  int conceal_update_lines = FALSE;
+  bool conceal_cursor_moved = false;
 
   if (char_avail())
     return;
@@ -1406,11 +1400,7 @@ ins_redraw (
       update_curswant();
       ins_apply_autocmds(EVENT_CURSORMOVEDI);
     }
-    if (curwin->w_p_cole > 0) {
-      conceal_old_cursor_line = last_cursormoved.lnum;
-      conceal_new_cursor_line = curwin->w_cursor.lnum;
-      conceal_update_lines = TRUE;
-    }
+    conceal_cursor_moved = true;
     last_cursormoved = curwin->w_cursor;
   }
 
@@ -1452,17 +1442,9 @@ ins_redraw (
     }
   }
 
-  if ((conceal_update_lines
-       && (conceal_old_cursor_line != conceal_new_cursor_line
-           || conceal_cursor_line(curwin)))
-      || need_cursor_line_redraw) {
-    if (conceal_old_cursor_line != conceal_new_cursor_line) {
-      redrawWinline(curwin, conceal_old_cursor_line);
-    }
-    redrawWinline(curwin, conceal_new_cursor_line == 0
-                  ? curwin->w_cursor.lnum : conceal_new_cursor_line);
-    curwin->w_valid &= ~VALID_CROW;
-    need_cursor_line_redraw = false;
+  if (curwin->w_p_cole > 0 && conceal_cursor_line(curwin)
+      && conceal_cursor_moved) {
+    redrawWinline(curwin, curwin->w_cursor.lnum);
   }
 
   if (must_redraw) {
diff --git a/src/nvim/globals.h b/src/nvim/globals.h
index f749c119cd..2550fb8163 100644
--- a/src/nvim/globals.h
+++ b/src/nvim/globals.h
@@ -918,10 +918,6 @@ EXTERN disptick_T display_tick INIT(= 0);
  * cursor position in Insert mode. */
 EXTERN linenr_T spell_redraw_lnum INIT(= 0);
 
-/* Set when the cursor line needs to be redrawn. */
-EXTERN int need_cursor_line_redraw INIT(= FALSE);
-
-
 #ifdef USE_MCH_ERRMSG
 // Grow array to collect error messages in until they can be displayed.
 EXTERN garray_T error_ga INIT(= GA_EMPTY_INIT_VALUE);
diff --git a/src/nvim/move.c b/src/nvim/move.c
index f2c8996050..07b355e603 100644
--- a/src/nvim/move.c
+++ b/src/nvim/move.c
@@ -105,14 +105,14 @@ void reset_cursorline(void)
 // Redraw when w_cline_row changes and 'relativenumber' or 'cursorline' is set.
 static void redraw_for_cursorline(win_T *wp)
 {
-  if ((wp->w_p_rnu || wp->w_p_cul)
+  if ((wp->w_p_rnu || win_cursorline_standout(wp))
       && (wp->w_valid & VALID_CROW) == 0
       && !pum_visible()) {
     if (wp->w_p_rnu) {
       // win_line() will redraw the number column only.
       redraw_win_later(wp, VALID);
     }
-    if (wp->w_p_cul) {
+    if (win_cursorline_standout(wp)) {
       if (wp->w_redr_type <= VALID && wp->w_last_cursorline != 0) {
         // "w_last_cursorline" may be outdated, worst case we redraw
         // too much.  This is optimized for moving the cursor around in
@@ -2207,7 +2207,7 @@ void do_check_cursorbind(void)
         int restart_edit_save = restart_edit;
         restart_edit = true;
         check_cursor();
-        if (curwin->w_p_cul || curwin->w_p_cuc) {
+        if (win_cursorline_standout(curwin) || curwin->w_p_cuc) {
           validate_cursor();
         }
         restart_edit = restart_edit_save;
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index 21c902a68e..32fa502940 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -64,12 +64,9 @@
 
 typedef struct normal_state {
   VimState state;
-  linenr_T conceal_old_cursor_line;
-  linenr_T conceal_new_cursor_line;
   bool command_finished;
   bool ctrl_w;
   bool need_flushbuf;
-  bool conceal_update_lines;
   bool set_prevcount;
   bool previous_got_int;             // `got_int` was true
   bool cmdwin;                       // command-line window normal mode
@@ -1201,12 +1198,6 @@ static void normal_check_cursor_moved(NormalState *s)
       apply_autocmds(EVENT_CURSORMOVED, NULL, NULL, false, curbuf);
     }
 
-    if (curwin->w_p_cole > 0) {
-      s->conceal_old_cursor_line = last_cursormoved.lnum;
-      s->conceal_new_cursor_line = curwin->w_cursor.lnum;
-      s->conceal_update_lines = true;
-    }
-
     last_cursormoved = curwin->w_cursor;
   }
 }
@@ -1246,24 +1237,11 @@ static void normal_redraw(NormalState *s)
   update_topline();
   validate_cursor();
 
-  // TODO(bfredl): this logic is only used for 'concealcursor', not
-  // 'cursorline'. Maybe we can eliminate this check (and in edit.c) by
-  // checking for 'concealcursor' wherever we check for 'cursorline'
-  if (s->conceal_update_lines
-      && (s->conceal_old_cursor_line !=
-        s->conceal_new_cursor_line
-        || conceal_cursor_line(curwin)
-        || need_cursor_line_redraw)) {
-    if (s->conceal_old_cursor_line !=
-        s->conceal_new_cursor_line
-        && s->conceal_old_cursor_line <=
-        curbuf->b_ml.ml_line_count) {
-      redrawWinline(curwin, s->conceal_old_cursor_line);
-    }
-
-    redrawWinline(curwin, s->conceal_new_cursor_line);
-    curwin->w_valid &= ~VALID_CROW;
-    need_cursor_line_redraw = false;
+  // If the cursor moves horizontally when 'concealcursor' is active, then the
+  // current line needs to be redrawn in order to calculate the correct
+  // cursor position.
+  if (curwin->w_p_cole > 0 && conceal_cursor_line(curwin)) {
+    redrawWinline(curwin, curwin->w_cursor.lnum);
   }
 
   if (VIsual_active) {
@@ -6500,9 +6478,6 @@ void may_start_select(int c)
  */
 static void n_start_visual_mode(int c)
 {
-  // Check for redraw before changing the state.
-  conceal_check_cursor_line();
-
   VIsual_mode = c;
   VIsual_active = true;
   VIsual_reselect = true;
@@ -7072,8 +7047,6 @@ static void nv_g_cmd(cmdarg_T *cap)
  */
 static void n_opencmd(cmdarg_T *cap)
 {
-  linenr_T oldline = curwin->w_cursor.lnum;
-
   if (!checkclearopq(cap->oap)) {
     if (cap->cmdchar == 'O')
       /* Open above the first line of a folded sequence of lines */
@@ -7092,10 +7065,7 @@ static void n_opencmd(cmdarg_T *cap)
                      has_format_option(FO_OPEN_COMS)
                      ? OPENLINE_DO_COM : 0,
                      0)) {
-      if (curwin->w_p_cole > 0 && oldline != curwin->w_cursor.lnum) {
-        redrawWinline(curwin, oldline);
-      }
-      if (curwin->w_p_cul) {
+      if (win_cursorline_standout(curwin)) {
         // force redraw of cursorline
         curwin->w_valid &= ~VALID_CROW;
       }
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index 68d95decff..a3f1f00db2 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -151,6 +151,8 @@ static bool send_grid_resize = false;
 /// Highlight ids are no longer valid. Force retransmission
 static bool highlights_invalid = false;
 
+static bool conceal_cursor_used = false;
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "screen.c.generated.h"
 #endif
@@ -505,19 +507,28 @@ int conceal_cursor_line(win_T *wp)
   return vim_strchr(wp->w_p_cocu, c) != NULL;
 }
 
-/*
- * Check if the cursor line needs to be redrawn because of 'concealcursor'.
- */
+// Check if the cursor line needs to be redrawn because of 'concealcursor'.
+//
+// When cursor is moved at the same time, both lines will be redrawn regardless.
 void conceal_check_cursor_line(void)
 {
-  if (curwin->w_p_cole > 0 && conceal_cursor_line(curwin)) {
-    need_cursor_line_redraw = TRUE;
-    /* Need to recompute cursor column, e.g., when starting Visual mode
-     * without concealing. */
-    curs_columns(TRUE);
+  bool should_conceal = conceal_cursor_line(curwin);
+  if (curwin->w_p_cole > 0 && (conceal_cursor_used != should_conceal)) {
+    redrawWinline(curwin, curwin->w_cursor.lnum);
+    // Need to recompute cursor column, e.g., when starting Visual mode
+    // without concealing. */
+    curs_columns(true);
   }
 }
 
+/// Whether cursorline is drawn in a special way
+///
+/// If true, both old and new cursorline will need
+/// need to be redrawn when moving cursor within windows.
+bool win_cursorline_standout(win_T *wp)
+{
+  return wp->w_p_cul || (wp->w_p_cole > 0 && !conceal_cursor_line(wp));
+}
 
 /*
  * Update a single window.
@@ -1942,6 +1953,7 @@ static void fold_line(win_T *wp, long fold_count, foldinfo_T *foldinfo, linenr_T
     curwin->w_cline_height = 1;
     curwin->w_cline_folded = true;
     curwin->w_valid |= (VALID_CHEIGHT|VALID_CROW);
+    conceal_cursor_used = conceal_cursor_line(curwin);
   }
 }
 
@@ -3960,6 +3972,7 @@ win_line (
         curwin->w_cline_height = row - startrow;
         curwin->w_cline_folded = false;
         curwin->w_valid |= (VALID_CHEIGHT|VALID_CROW);
+        conceal_cursor_used = conceal_cursor_line(curwin);
       }
 
       break;
diff --git a/src/nvim/window.c b/src/nvim/window.c
index 35ca5c61e8..3cadfe612a 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -3547,7 +3547,7 @@ void win_goto(win_T *wp)
     redrawWinline(owp, owp->w_cursor.lnum);
   }
   if (curwin->w_p_cole > 0 && !msg_scrolled) {
-    need_cursor_line_redraw = true;
+    redrawWinline(curwin, curwin->w_cursor.lnum);
   }
 }