Reduce pum redraws from edit.c by delaying undisplay of pum

This makes it possible for the compositor to compare the old pum with
the new position, and only clear what is necessary.

src/nvim/edit.c

@@ -473,6 +473,8 @@ static void insert_enter(InsertState *s)
     o_lnum = curwin->w_cursor.lnum;
   }
 
+  pum_check_clear();
+
   foldUpdateAfterInsert();
   // When CTRL-C was typed got_int will be set, with the result
   // that the autocommands won't be executed. When mapped got_int
@@ -1447,6 +1449,7 @@ ins_redraw (
     redrawWinline(curwin, curwin->w_cursor.lnum);
   }
 
+  pum_check_clear();
   if (must_redraw) {
     update_screen(0);
   } else if (clear_cmdline || redraw_cmdline) {
@@ -2490,20 +2493,10 @@ void set_completion(colnr_T startcol, list_T *list)
 static pumitem_T *compl_match_array = NULL;
 static int compl_match_arraysize;
 
+
 /*
  * Update the screen and when there is any scrolling remove the popup menu.
  */
-static void ins_compl_upd_pum(void)
-{
-  int h;
-
-  if (compl_match_array != NULL) {
-    h = curwin->w_cline_height;
-    update_screen(0);
-    if (h != curwin->w_cline_height)
-      ins_compl_del_pum();
-  }
-}
 
 /*
  * Remove any popup menu.
@@ -2511,7 +2504,7 @@ static void ins_compl_upd_pum(void)
 static void ins_compl_del_pum(void)
 {
   if (compl_match_array != NULL) {
-    pum_undisplay();
+    pum_undisplay(false);
     xfree(compl_match_array);
     compl_match_array = NULL;
   }
@@ -4305,17 +4298,14 @@ ins_compl_next (
   }
 
   if (!allow_get_expansion) {
-    /* may undisplay the popup menu first */
-    ins_compl_upd_pum();
-
-    /* redraw to show the user what was inserted */
+    // redraw to show the user what was inserted
     update_screen(0);
 
-    /* display the updated popup menu */
+    // display the updated popup menu
     ins_compl_show_pum();
 
-    /* Delete old text to be replaced, since we're still searching and
-     * don't want to match ourselves!  */
+    // Delete old text to be replaced, since we're still searching and
+    // don't want to match ourselves!
     ins_compl_delete();
   }
 
@@ -4862,8 +4852,6 @@ static int ins_complete(int c, bool enable_pum)
   save_w_leftcol = curwin->w_leftcol;
   n = ins_compl_next(true, ins_compl_key2count(c), insert_match, false);
 
-  /* may undisplay the popup menu */
-  ins_compl_upd_pum();
 
   if (n > 1)            /* all matches have been found */
     compl_matches = n;
@@ -7939,7 +7927,6 @@ static void ins_mouse(int c)
 static void ins_mousescroll(int dir)
 {
   win_T *const old_curwin = curwin;
-  bool did_scroll = false;
   pos_T tpos = curwin->w_cursor;
 
   if (mouse_row >= 0 && mouse_col >= 0) {
@@ -7969,7 +7956,6 @@ static void ins_mousescroll(int dir)
     } else {
         mouse_scroll_horiz(dir);
     }
-    did_scroll = true;
   }
 
   curwin->w_redr_status = TRUE;
@@ -7977,14 +7963,6 @@ static void ins_mousescroll(int dir)
   curwin = old_curwin;
   curbuf = curwin->w_buffer;
 
-  /* The popup menu may overlay the window, need to redraw it.
-   * TODO: Would be more efficient to only redraw the windows that are
-   * overlapped by the popup menu. */
-  if (pum_visible() && did_scroll) {
-    redraw_all_later(NOT_VALID);
-    ins_compl_show_pum();
-  }
-
   if (!equalpos(curwin->w_cursor, tpos)) {
     start_arrow(&tpos);
     can_cindent = true;

src/nvim/popupmnu.c

@@ -42,6 +42,7 @@ static int pum_row;                 // top row of pum
 static int pum_col;                 // left column of pum
 
 static bool pum_is_visible = false;
+static bool pum_is_drawn = false;
 static bool pum_external = false;
 
 static ScreenGrid pum_grid = SCREEN_GRID_INIT;
@@ -88,6 +89,7 @@ void pum_display(pumitem_T *array, int size, int selected, bool array_changed)
     // Mark the pum as visible already here,
     // to avoid that must_redraw is set when 'cursorcolumn' is on.
     pum_is_visible = true;
+    pum_is_drawn = true;
     validate_cursor_col();
     above_row = 0;
     below_row = cmdline_row;
@@ -730,6 +732,8 @@ static int pum_set_selected(int n, int repeat)
 
             // Update the screen before drawing the popup menu.
             // Enable updating the status lines.
+            // TODO(bfredl): can simplify, get rid of the flag munging?
+            // or at least eliminate extra redraw before win_enter()?
             pum_is_visible = false;
             update_screen(0);
             pum_is_visible = true;
@@ -759,17 +763,27 @@ static int pum_set_selected(int n, int repeat)
 }
 
 /// Undisplay the popup menu (later).
-void pum_undisplay(void)
+void pum_undisplay(bool immediate)
 {
   pum_is_visible = false;
   pum_array = NULL;
 
-  if (pum_external) {
-    ui_call_popupmenu_hide();
-  } else {
-    ui_comp_remove_grid(&pum_grid);
-    // TODO(bfredl): consider the possibility of keeping float grids allocated.
-    grid_free(&pum_grid);
+  if (immediate) {
+    pum_check_clear();
+  }
+}
+
+void pum_check_clear(void)
+{
+  if (!pum_is_visible && pum_is_drawn) {
+    if (pum_external) {
+      ui_call_popupmenu_hide();
+    } else {
+      ui_comp_remove_grid(&pum_grid);
+      // TODO(bfredl): consider keeping float grids allocated.
+      grid_free(&pum_grid);
+    }
+    pum_is_drawn = false;
   }
 }
 

src/nvim/screen.c

@@ -7203,7 +7203,6 @@ void screen_resize(int width, int height)
       } else {
         update_topline();
         if (pum_drawn()) {
-          redraw_later(NOT_VALID);
           ins_compl_show_pum();
         }
         update_screen(NOT_VALID);