feat(messages)!: graduate the 'msgsep' feature

The old behaviour (e.g. via `set display-=msgsep`) will not be available.
Assuming that messages always are being drawn on msg_grid
(or not drawn at all, and forwarded to `ext_messages` enabled UI)
will allows some simplifcations and enhancements moving forward.

18 files changed, 79 insertions, 420 deletions

diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 15fc551dd9..065fe1af70 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -2128,7 +2128,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 	security reasons.
 
 					*'display'* *'dy'*
-'display' 'dy'		string	(default "lastline,msgsep")
+'display' 'dy'		string	(default "lastline")
 			global
 	Change the way text is displayed.  This is a comma-separated list of
 	flags:
@@ -2140,10 +2140,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 			column of the last screen line.  Overrules "lastline".
 	uhex		Show unprintable characters hexadecimal as <xx>
 			instead of using ^C and ~C.
-	msgsep		When showing messages longer than 'cmdheight', only
-			scroll the message lines, not the entire screen. The
-			separator line is decorated by |hl-MsgSeparator| and
-			the "msgsep" flag of 'fillchars'.
+	msgsep		Obsolete flag. Allowed but takes no effect. |msgsep|
 
 	When neither "lastline" nor "truncate" is included, a last line that
 	doesn't fit is replaced with "@" lines.
diff --git a/runtime/doc/syntax.txt b/runtime/doc/syntax.txt
index 8ebe0f3569..74778addc7 100644
--- a/runtime/doc/syntax.txt
+++ b/runtime/doc/syntax.txt
@@ -5187,7 +5187,7 @@ ModeMsg		'showmode' message (e.g., "-- INSERT --").
 							*hl-MsgArea*
 MsgArea		Area for messages and cmdline.
 							*hl-MsgSeparator*
-MsgSeparator	Separator for scrolled messages, `msgsep` flag of 'display'.
+MsgSeparator	Separator for scrolled messages |msgsep|.
 							*hl-MoreMsg*
 MoreMsg		|more-prompt|
 							*hl-NonText*
diff --git a/runtime/doc/ui.txt b/runtime/doc/ui.txt
index 7ce6cd251f..5685979c82 100644
--- a/runtime/doc/ui.txt
+++ b/runtime/doc/ui.txt
@@ -608,12 +608,12 @@ tabs.
 	Close the window.
 
 ["msg_set_pos", grid, row, scrolled, sep_char] ~
-	Display messages on `grid`.  The grid will be displayed at `row` on the
-	default grid (grid=1), covering the full column width. `scrolled`
+	Display messages on `grid`.  The grid will be displayed at `row` on
+	the default grid (grid=1), covering the full column width. `scrolled`
 	indicates whether the message area has been scrolled to cover other
-	grids. It can be useful to draw a separator then ('display' msgsep
-	flag). The Builtin TUI draws a full line filled with `sep_char` and
-	|hl-MsgSeparator| highlight.
+	grids. It can be useful to draw a separator then |msgsep|. The Builtin
+	TUI draws a full line filled with `sep_char` ('fillchars' msgsep
+	field) and |hl-MsgSeparator| highlight.
 
 	When |ui-messages| is active, no message grid is used, and this event
 	will not be sent.
diff --git a/runtime/doc/vim_diff.txt b/runtime/doc/vim_diff.txt
index 672d064478..7c1658df76 100644
--- a/runtime/doc/vim_diff.txt
+++ b/runtime/doc/vim_diff.txt
@@ -38,7 +38,7 @@ centralized reference of the differences.
 - 'complete' excludes "i"
 - 'cscopeverbose' is enabled
 - 'directory' defaults to ~/.local/state/nvim/swap// (|xdg|), auto-created
-- 'display' defaults to "lastline,msgsep"
+- 'display' defaults to "lastline"
 - 'encoding' is UTF-8 (cf. 'fileencoding' for file-content encoding)
 - 'fillchars' defaults (in effect) to "vert:│,fold:·,sep:│"
 - 'formatoptions' defaults to "tcqj"
@@ -256,9 +256,8 @@ Normal commands:
 
 Options:
   'cpoptions'   flags: |cpo-_|
-  'display'     flags: "msgsep" minimizes scrolling when showing messages
   'guicursor'   works in the terminal
-  'fillchars'   flags: "msgsep" (see 'display'), "horiz", "horizup",
+  'fillchars'   flags: "msgsep", "horiz", "horizup",
                 "horizdown", "vertleft", "vertright", "verthoriz"
   'foldcolumn'  supports up to 9 dynamic/fixed columns
   'inccommand'  shows interactive results for |:substitute|-like commands
@@ -479,6 +478,11 @@ TUI:
 UI/Display:
   |Visual| selection highlights the character at cursor. |visual-use|
 
+  messages: When showing messages longer than 'cmdheight', only
+  scroll the message lines, not the entire screen. The
+  separator line is decorated by |hl-MsgSeparator| and
+  the "msgsep" flag of 'fillchars'. *msgsep*
+
 Vimscript compatibility:
   `count` does not alias to |v:count|
   `errmsg` does not alias to |v:errmsg|
diff --git a/src/nvim/drawscreen.c b/src/nvim/drawscreen.c
index 7ad4193058..15a7294496 100644
--- a/src/nvim/drawscreen.c
+++ b/src/nvim/drawscreen.c
@@ -428,74 +428,41 @@ int update_screen(void)
                         msg_grid.cols, false);
       }
     }
-    if (msg_use_msgsep()) {
-      msg_grid.throttled = false;
-      bool was_invalidated = false;
-
-      // UPD_CLEAR is already handled
-      if (type == UPD_NOT_VALID && !ui_has(kUIMultigrid) && msg_scrolled) {
-        was_invalidated = ui_comp_set_screen_valid(false);
-        for (int i = valid; i < Rows - p_ch; i++) {
-          grid_clear_line(&default_grid, default_grid.line_offset[i],
-                          Columns, false);
+    msg_grid.throttled = false;
+    bool was_invalidated = false;
+
+    // UPD_CLEAR is already handled
+    if (type == UPD_NOT_VALID && !ui_has(kUIMultigrid) && msg_scrolled) {
+      was_invalidated = ui_comp_set_screen_valid(false);
+      for (int i = valid; i < Rows - p_ch; i++) {
+        grid_clear_line(&default_grid, default_grid.line_offset[i],
+                        Columns, false);
+      }
+      FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
+        if (wp->w_floating) {
+          continue;
         }
-        FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
-          if (wp->w_floating) {
-            continue;
-          }
-          if (W_ENDROW(wp) > valid) {
-            // TODO(bfredl): too pessimistic. type could be UPD_NOT_VALID
-            // only because windows that are above the separator.
-            wp->w_redr_type = MAX(wp->w_redr_type, UPD_NOT_VALID);
-          }
-          if (!is_stl_global && W_ENDROW(wp) + wp->w_status_height > valid) {
-            wp->w_redr_status = true;
-          }
+        if (W_ENDROW(wp) > valid) {
+          // TODO(bfredl): too pessimistic. type could be UPD_NOT_VALID
+          // only because windows that are above the separator.
+          wp->w_redr_type = MAX(wp->w_redr_type, UPD_NOT_VALID);
         }
-        if (is_stl_global && Rows - p_ch - 1 > valid) {
-          curwin->w_redr_status = true;
+        if (!is_stl_global && W_ENDROW(wp) + wp->w_status_height > valid) {
+          wp->w_redr_status = true;
         }
       }
-      msg_grid_set_pos(Rows - (int)p_ch, false);
-      msg_grid_invalid = false;
-      if (was_invalidated) {
-        // screen was only invalid for the msgarea part.
-        // @TODO(bfredl): using the same "valid" flag
-        // for both messages and floats moving is bit of a mess.
-        ui_comp_set_screen_valid(true);
-      }
-    } else if (type != UPD_CLEAR) {
-      if (msg_scrolled > Rows - 5) {  // redrawing is faster
-        type = UPD_NOT_VALID;
-      } else {
-        check_for_delay(false);
-        grid_ins_lines(&default_grid, 0, msg_scrolled, Rows, 0, Columns);
-        FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
-          if (wp->w_floating) {
-            continue;
-          }
-          if (wp->w_winrow < msg_scrolled) {
-            if (W_ENDROW(wp) > msg_scrolled
-                && wp->w_redr_type < UPD_REDRAW_TOP
-                && wp->w_lines_valid > 0
-                && wp->w_topline == wp->w_lines[0].wl_lnum) {
-              wp->w_upd_rows = msg_scrolled - wp->w_winrow;
-              wp->w_redr_type = UPD_REDRAW_TOP;
-            } else {
-              wp->w_redr_type = UPD_NOT_VALID;
-              if (wp->w_winrow + wp->w_winbar_height <= msg_scrolled) {
-                wp->w_redr_status = true;
-              }
-            }
-          }
-        }
-        if (is_stl_global && Rows - p_ch - 1 <= msg_scrolled) {
-          curwin->w_redr_status = true;
-        }
-        redraw_cmdline = true;
-        redraw_tabline = true;
+      if (is_stl_global && Rows - p_ch - 1 > valid) {
+        curwin->w_redr_status = true;
       }
     }
+    msg_grid_set_pos(Rows - (int)p_ch, false);
+    msg_grid_invalid = false;
+    if (was_invalidated) {
+      // screen was only invalid for the msgarea part.
+      // @TODO(bfredl): using the same "valid" flag
+      // for both messages and floats moving is bit of a mess.
+      ui_comp_set_screen_valid(true);
+    }
     msg_scrolled = 0;
     msg_scrolled_at_flush = 0;
     need_wait_return = false;
@@ -526,9 +493,8 @@ int update_screen(void)
     default_grid.valid = true;
   }
 
-  // After disabling msgsep the grid might not have been deallocated yet,
-  // hence we also need to check msg_grid.chars
-  if (type == UPD_NOT_VALID && (msg_use_grid() || msg_grid.chars)) {
+  // might need to clear space on default_grid for the message area.
+  if (type == UPD_NOT_VALID && clear_cmdline && !ui_has(kUIMessages)) {
     grid_fill(&default_grid, Rows - (int)p_ch, Rows, 0, Columns, ' ', ' ', 0);
   }
 
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index 73ce92c823..5591b5f55d 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -6124,9 +6124,6 @@ static void ex_redrawstatus(exarg_T *eap)
   } else {
     status_redraw_curbuf();
   }
-  if (msg_scrolled && !msg_use_msgsep() && (State & MODE_CMDLINE)) {
-    return;  // redraw later
-  }
 
   RedrawingDisabled = 0;
   p_lz = false;
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index d1d0fe3f2a..6883dc5b14 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -775,7 +775,7 @@ static uint8_t *command_line_enter(int firstc, long count, int indent, bool init
 
   // Redraw the statusline in case it uses the current mode using the mode()
   // function.
-  if (!cmd_silent && (msg_scrolled == 0 || msg_use_msgsep())) {
+  if (!cmd_silent) {
     bool found_one = false;
 
     FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
diff --git a/src/nvim/message.c b/src/nvim/message.c
index d6835e04eb..fef5055c84 100644
--- a/src/nvim/message.c
+++ b/src/nvim/message.c
@@ -153,8 +153,7 @@ void msg_grid_set_pos(int row, bool scrolled)
 
 bool msg_use_grid(void)
 {
-  return default_grid.chars && msg_use_msgsep()
-         && !ui_has(kUIMessages);
+  return default_grid.chars && !ui_has(kUIMessages);
 }
 
 void msg_grid_validate(void)
@@ -172,19 +171,17 @@ void msg_grid_validate(void)
     xfree(msg_grid.dirty_col);
     msg_grid.dirty_col = xcalloc((size_t)Rows, sizeof(*msg_grid.dirty_col));
 
-    // Tricky: allow resize while pager is active
-    int pos = msg_scrolled ? msg_grid_pos : max_rows;
+    // Tricky: allow resize while pager or ex mode is active
+    int pos = MAX(max_rows - msg_scrolled, 0);
+    msg_grid.throttled = false;  // don't throttle in 'cmdheight' area
+    msg_grid_set_pos(pos, msg_scrolled);
     ui_comp_put_grid(&msg_grid, pos, 0, msg_grid.rows, msg_grid.cols,
                      false, true);
     ui_call_grid_resize(msg_grid.handle, msg_grid.cols, msg_grid.rows);
 
-    msg_grid.throttled = false;  // don't throttle in 'cmdheight' area
     msg_scrolled_at_flush = msg_scrolled;
     msg_grid.focusable = false;
     msg_grid_adj.target = &msg_grid;
-    if (!msg_scrolled) {
-      msg_grid_set_pos(max_rows, false);
-    }
   } else if (!should_alloc && msg_grid.chars) {
     ui_comp_remove_grid(&msg_grid);
     grid_free(&msg_grid);
@@ -2336,13 +2333,6 @@ int msg_scrollsize(void)
   return msg_scrolled + (int)p_ch + ((p_ch > 0 || msg_scrolled > 1) ? 1 : 0);
 }
 
-bool msg_use_msgsep(void)
-{
-  // the full-screen scroll behavior doesn't really make sense with
-  // 'ext_multigrid'
-  return (dy_flags & DY_MSGSEP) || p_ch == 0 || ui_has(kUIMultigrid);
-}
-
 bool msg_do_throttle(void)
 {
   return msg_use_grid() && !(rdb_flags & RDB_NOTHROTTLE);
@@ -2355,23 +2345,19 @@ void msg_scroll_up(bool may_throttle, bool zerocmd)
     msg_grid.throttled = true;
   }
   msg_did_scroll = true;
-  if (msg_use_msgsep()) {
-    if (msg_grid_pos > 0) {
-      msg_grid_set_pos(msg_grid_pos - 1, !zerocmd);
-
-      // When displaying the first line with cmdheight=0, we need to draw over
-      // the existing last line of the screen.
-      if (zerocmd && msg_grid.chars) {
-        grid_clear_line(&msg_grid, msg_grid.line_offset[0], msg_grid.cols, false);
-      }
-    } else {
-      grid_del_lines(&msg_grid, 0, 1, msg_grid.rows, 0, msg_grid.cols);
-      memmove(msg_grid.dirty_col, msg_grid.dirty_col + 1,
-              (size_t)(msg_grid.rows - 1) * sizeof(*msg_grid.dirty_col));
-      msg_grid.dirty_col[msg_grid.rows - 1] = 0;
+  if (msg_grid_pos > 0) {
+    msg_grid_set_pos(msg_grid_pos - 1, !zerocmd);
+
+    // When displaying the first line with cmdheight=0, we need to draw over
+    // the existing last line of the screen.
+    if (zerocmd && msg_grid.chars) {
+      grid_clear_line(&msg_grid, msg_grid.line_offset[0], msg_grid.cols, false);
     }
   } else {
-    grid_del_lines(&msg_grid_adj, 0, 1, Rows, 0, Columns);
+    grid_del_lines(&msg_grid, 0, 1, msg_grid.rows, 0, msg_grid.cols);
+    memmove(msg_grid.dirty_col, msg_grid.dirty_col + 1,
+            (size_t)(msg_grid.rows - 1) * sizeof(*msg_grid.dirty_col));
+    msg_grid.dirty_col[msg_grid.rows - 1] = 0;
   }
 
   grid_fill(&msg_grid_adj, Rows - 1, Rows, 0, Columns, ' ', ' ', HL_ATTR(HLF_MSG));
@@ -2436,21 +2422,17 @@ void msg_reset_scroll(void)
   }
   // TODO(bfredl): some duplicate logic with update_screen(). Later on
   // we should properly disentangle message clear with full screen redraw.
-  if (msg_use_grid()) {
-    msg_grid.throttled = false;
-    // TODO(bfredl): risk for extra flicker i e with
-    // "nvim -o has_swap also_has_swap"
-    msg_grid_set_pos(Rows - (int)p_ch, false);
-    clear_cmdline = true;
-    if (msg_grid.chars) {
-      // non-displayed part of msg_grid is considered invalid.
-      for (int i = 0; i < MIN(msg_scrollsize(), msg_grid.rows); i++) {
-        grid_clear_line(&msg_grid, msg_grid.line_offset[i],
-                        msg_grid.cols, false);
-      }
+  msg_grid.throttled = false;
+  // TODO(bfredl): risk for extra flicker i e with
+  // "nvim -o has_swap also_has_swap"
+  msg_grid_set_pos(Rows - (int)p_ch, false);
+  clear_cmdline = true;
+  if (msg_grid.chars) {
+    // non-displayed part of msg_grid is considered invalid.
+    for (int i = 0; i < MIN(msg_scrollsize(), msg_grid.rows); i++) {
+      grid_clear_line(&msg_grid, msg_grid.line_offset[i],
+                      msg_grid.cols, false);
     }
-  } else {
-    redraw_all_later(UPD_NOT_VALID);
   }
   msg_scrolled = 0;
   msg_scrolled_at_flush = 0;
diff --git a/src/nvim/option_defs.h b/src/nvim/option_defs.h
index e27607d7a8..4e48c992c2 100644
--- a/src/nvim/option_defs.h
+++ b/src/nvim/option_defs.h
@@ -492,7 +492,7 @@ EXTERN unsigned dy_flags;
 #define DY_LASTLINE             0x001
 #define DY_TRUNCATE             0x002
 #define DY_UHEX                 0x004
-// code should use msg_use_msgsep() to check if msgsep is active
+// legacy flag, not used
 #define DY_MSGSEP               0x008
 EXTERN int p_ed;                // 'edcompatible'
 EXTERN char *p_ead;             // 'eadirection'
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index 048d9e112b..82fd0d7428 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -660,7 +660,7 @@ return {
       deny_duplicates=true,
       redraw={'all_windows'},
       varname='p_dy',
-      defaults={if_true="lastline,msgsep"}
+      defaults={if_true="lastline"}
     },
     {
       full_name='eadirection', abbreviation='ead',
diff --git a/test/functional/core/fileio_spec.lua b/test/functional/core/fileio_spec.lua
index a589d088a4..d1ff5b8036 100644
--- a/test/functional/core/fileio_spec.lua
+++ b/test/functional/core/fileio_spec.lua
@@ -166,7 +166,7 @@ describe('fileio', function()
       [3] = {bold = true, foreground = Screen.colors.SeaGreen4}
     })
     screen:attach()
-    command("set display-=msgsep shortmess-=F")
+    command("set shortmess-=F")
 
     command("e Xtest-overwrite-forced")
     screen:expect([[
diff --git a/test/functional/legacy/cmdline_spec.lua b/test/functional/legacy/cmdline_spec.lua
index 49e3825693..88912b9cd4 100644
--- a/test/functional/legacy/cmdline_spec.lua
+++ b/test/functional/legacy/cmdline_spec.lua
@@ -172,83 +172,6 @@ describe('cmdline', function()
                                     |
     ]])
   end)
-
-  -- oldtest: Test_redrawstatus_in_autocmd()
-  it(':redrawstatus in cmdline mode', function()
-    local screen = Screen.new(60, 8)
-    screen:set_default_attr_ids({
-      [0] = {bold = true, foreground = Screen.colors.Blue},  -- NonText
-      [1] = {bold = true, reverse = true},  -- MsgSeparator, StatusLine
-    })
-    screen:attach()
-    exec([[
-      set laststatus=2
-      set statusline=%=:%{getcmdline()}
-      autocmd CmdlineChanged * redrawstatus
-      set display-=msgsep
-    ]])
-    -- :redrawstatus is postponed if messages have scrolled
-    feed([[:echo "one\ntwo\nthree\nfour"<CR>]])
-    feed(':foobar')
-    screen:expect([[
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {1:                               :echo "one\ntwo\nthree\nfour"}|
-      one                                                         |
-      two                                                         |
-      three                                                       |
-      four                                                        |
-      :foobar^                                                     |
-    ]])
-    -- it is not postponed if messages have not scrolled
-    feed('<Esc>:for in in range(3)')
-    screen:expect([[
-                                                                  |
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {1:                                         :for in in range(3)}|
-      :for in in range(3)^                                         |
-    ]])
-    -- with cmdheight=1 messages have scrolled when typing :endfor
-    feed('<CR>:endfor')
-    screen:expect([[
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {1:                                         :for in in range(3)}|
-      :for in in range(3)                                         |
-      :  :endfor^                                                  |
-    ]])
-    feed('<CR>:set cmdheight=2<CR>')
-    -- with cmdheight=2 messages haven't scrolled when typing :for or :endfor
-    feed(':for in in range(3)')
-    screen:expect([[
-                                                                  |
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {1:                                         :for in in range(3)}|
-      :for in in range(3)^                                         |
-                                                                  |
-    ]])
-    feed('<CR>:endfor')
-    screen:expect([[
-                                                                  |
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {0:~                                                           }|
-      {1:                                                    ::endfor}|
-      :for in in range(3)                                         |
-      :  :endfor^                                                  |
-    ]])
-  end)
 end)
 
 describe('cmdwin', function()
diff --git a/test/functional/ui/cmdline_spec.lua b/test/functional/ui/cmdline_spec.lua
index 1528b5307d..8003947078 100644
--- a/test/functional/ui/cmdline_spec.lua
+++ b/test/functional/ui/cmdline_spec.lua
@@ -822,7 +822,7 @@ describe('statusline is redrawn on entering cmdline', function()
     ]]}
   end)
 
-  it('with scrolled messages and msgsep', function()
+  it('with scrolled messages', function()
     screen:try_resize(35,14)
     exec([[
       let g:count = 0
@@ -904,70 +904,6 @@ describe('statusline is redrawn on entering cmdline', function()
     ]]}
   end)
 
-  it('but not with scrolled messages without msgsep', function()
-    screen:try_resize(35,10)
-    exec([[
-      let g:count = 0
-      autocmd CmdlineEnter * let g:count += 1
-      set display-=msgsep
-      set statusline=%{mode()}%{g:count}
-    ]])
-    feed(':echoerr doesnotexist<cr>')
-    screen:expect{grid=[[
-      {1:~                                  }|
-      {1:~                                  }|
-      {1:~                                  }|
-      {1:~                                  }|
-      {1:~                                  }|
-      {3:c1                                 }|
-      {4:E121: Undefined variable: doesnotex}|
-      {4:ist}                                |
-      {5:Press ENTER or type command to cont}|
-      {5:inue}^                               |
-    ]]}
-    feed(':echoerr doesnotexist<cr>')
-    screen:expect{grid=[[
-      {1:~                                  }|
-      {1:~                                  }|
-      {3:c1                                 }|
-      {4:E121: Undefined variable: doesnotex}|
-      {4:ist}                                |
-      {5:Press ENTER or type command to cont}|
-      {4:E121: Undefined variable: doesnotex}|
-      {4:ist}                                |
-      {5:Press ENTER or type command to cont}|
-      {5:inue}^                               |
-    ]]}
-
-    feed(':echoerr doesnotexist<cr>')
-    screen:expect{grid=[[
-      {4:E121: Undefined variable: doesnotex}|
-      {4:ist}                                |
-      {5:Press ENTER or type command to cont}|
-      {4:E121: Undefined variable: doesnotex}|
-      {4:ist}                                |
-      {5:Press ENTER or type command to cont}|
-      {4:E121: Undefined variable: doesnotex}|
-      {4:ist}                                |
-      {5:Press ENTER or type command to cont}|
-      {5:inue}^                               |
-    ]]}
-
-    feed('<cr>')
-    screen:expect{grid=[[
-      ^                                   |
-      {1:~                                  }|
-      {1:~                                  }|
-      {1:~                                  }|
-      {1:~                                  }|
-      {1:~                                  }|
-      {1:~                                  }|
-      {1:~                                  }|
-      {3:n3                                 }|
-                                         |
-    ]]}
-  end)
-
   describe('if custom statusline is set by', function()
     before_each(function()
       command('set statusline=')
diff --git a/test/functional/ui/embed_spec.lua b/test/functional/ui/embed_spec.lua
index 92f5beebf5..e7addd1b85 100644
--- a/test/functional/ui/embed_spec.lua
+++ b/test/functional/ui/embed_spec.lua
@@ -82,20 +82,6 @@ local function test_embed(ext_linegrid)
       eq(Screen.colors.Green, screen.default_colors.rgb_bg)
     end}
   end)
-
-  it("set display-=msgsep before first redraw", function()
-    startup('--cmd', 'set display-=msgsep')
-    screen:expect{grid=[[
-      ^                                                            |
-      {3:~                                                           }|
-      {3:~                                                           }|
-      {3:~                                                           }|
-      {3:~                                                           }|
-      {3:~                                                           }|
-      {3:~                                                           }|
-                                                                  |
-    ]]}
-  end)
 end
 
 describe('--embed UI on startup (ext_linegrid=true)', function() test_embed(true) end)
diff --git a/test/functional/ui/highlight_spec.lua b/test/functional/ui/highlight_spec.lua
index 5ffe9ddaad..504a38d591 100644
--- a/test/functional/ui/highlight_spec.lua
+++ b/test/functional/ui/highlight_spec.lua
@@ -1560,17 +1560,6 @@ describe("MsgSeparator highlight and msgsep fillchar", function()
         1 %a   "[No Name]"                    line 1    |
       {3:Press ENTER or type command to continue}^           |
     ]])
-
-    -- when display doesn't contain msgsep, these options have no effect
-    feed_command("set display-=msgsep")
-    feed_command("ls")
-    screen:expect([[
-      {1:~                                                 }|
-      {1:~                                                 }|
-      :ls                                               |
-        1 %a   "[No Name]"                    line 1    |
-      {3:Press ENTER or type command to continue}^           |
-    ]])
   end)
 
   it("and MsgArea", function()
diff --git a/test/functional/ui/messages_spec.lua b/test/functional/ui/messages_spec.lua
index d6dfcf2aa9..0898d7fe75 100644
--- a/test/functional/ui/messages_spec.lua
+++ b/test/functional/ui/messages_spec.lua
@@ -1200,28 +1200,6 @@ vimComment     xxx match /\s"[^\-:.%#=*].*$/ms=s+1,lc=1  excludenl contains=@vim
   it('prints lines in Ex mode correctly with a burst of carriage returns #19341', function()
     command('set number')
     meths.buf_set_lines(0, 0, 0, true, {'aaa', 'bbb', 'ccc'})
-    command('set display-=msgsep')
-    feed('gggQ<CR><CR>1<CR><CR>vi')
-    screen:expect([[
-      Entering Ex mode.  Type "visual" to go to Normal mode.      |
-      {11:  2 }bbb                                                     |
-      {11:  3 }ccc                                                     |
-      :1                                                          |
-      {11:  1 }aaa                                                     |
-      {11:  2 }bbb                                                     |
-      :vi^                                                         |
-    ]])
-    feed('<CR>')
-    screen:expect([[
-      {11:  1 }aaa                                                     |
-      {11:  2 }^bbb                                                     |
-      {11:  3 }ccc                                                     |
-      {11:  4 }                                                        |
-      {1:~                                                           }|
-      {1:~                                                           }|
-                                                                  |
-    ]])
-    command('set display+=msgsep')
     feed('gggQ<CR><CR>1<CR><CR>vi')
     screen:expect([[
       Entering Ex mode.  Type "visual" to go to Normal mode.      |
diff --git a/test/functional/ui/screen_basic_spec.lua b/test/functional/ui/screen_basic_spec.lua
index 6c872e52d3..58c8238c35 100644
--- a/test/functional/ui/screen_basic_spec.lua
+++ b/test/functional/ui/screen_basic_spec.lua
@@ -682,30 +682,7 @@ local function screen_tests(linegrid)
       ]])
     end)
 
-    it('execute command with multi-line output without msgsep', function()
-      command("set display-=msgsep")
-      feed(':ls<cr>')
-      screen:expect([[
-        {0:~                                                    }|
-        {0:~                                                    }|
-        {0:~                                                    }|
-        {0:~                                                    }|
-        {0:~                                                    }|
-        {0:~                                                    }|
-        {0:~                                                    }|
-        {0:~                                                    }|
-        {0:~                                                    }|
-        {0:~                                                    }|
-        {0:~                                                    }|
-        :ls                                                  |
-          1 %a   "[No Name]"                    line 1       |
-        {7:Press ENTER or type command to continue}^              |
-      ]])
-      feed('<cr>') --  skip the "Press ENTER..." state or tests will hang
-    end)
-
-    it('execute command with multi-line output and with msgsep', function()
-      command("set display+=msgsep")
+    it('execute command with multi-line output', function()
       feed(':ls<cr>')
       screen:expect([[
                                                              |
@@ -1050,39 +1027,3 @@ describe('Screen default colors', function()
     end}
   end)
 end)
-
-
-describe('screen with msgsep deactivated on startup', function()
-  local screen
-
-  before_each(function()
-    clear('--cmd', 'set display-=msgsep')
-    screen = Screen.new()
-    screen:attach()
-    screen:set_default_attr_ids {
-      [0] = {bold=true, foreground=255};
-      [7] = {bold = true, foreground = Screen.colors.SeaGreen};
-    }
-  end)
-
-  it('execute command with multi-line output', function()
-    feed ':ls<cr>'
-    screen:expect([[
-      {0:~                                                    }|
-      {0:~                                                    }|
-      {0:~                                                    }|
-      {0:~                                                    }|
-      {0:~                                                    }|
-      {0:~                                                    }|
-      {0:~                                                    }|
-      {0:~                                                    }|
-      {0:~                                                    }|
-      {0:~                                                    }|
-      {0:~                                                    }|
-      :ls                                                  |
-        1 %a   "[No Name]"                    line 1       |
-      {7:Press ENTER or type command to continue}^              |
-    ]])
-    feed '<cr>'  -- skip the "Press ENTER..." state or tests will hang
-  end)
-end)
diff --git a/test/functional/ui/wildmode_spec.lua b/test/functional/ui/wildmode_spec.lua
index 58ffa3bda8..f1e818119e 100644
--- a/test/functional/ui/wildmode_spec.lua
+++ b/test/functional/ui/wildmode_spec.lua
@@ -184,11 +184,10 @@ describe("'wildmenu'", function()
     screen:expect_unchanged()
   end)
 
-  it('wildmode=list,full and display+=msgsep interaction #10092', function()
+  it('wildmode=list,full and messages interaction #10092', function()
     -- Need more than 5 rows, else tabline is covered and will be redrawn.
     screen:try_resize(25, 7)
 
-    command('set display+=msgsep')
     command('set wildmenu wildmode=list,full')
     command('set showtabline=2')
     feed(':set wildm<tab>')
@@ -223,44 +222,6 @@ describe("'wildmenu'", function()
     ]])
   end)
 
-  it('wildmode=list,full and display-=msgsep interaction', function()
-    -- Need more than 5 rows, else tabline is covered and will be redrawn.
-    screen:try_resize(25, 7)
-
-    command('set display-=msgsep')
-    command('set wildmenu wildmode=list,full')
-    feed(':set wildm<tab>')
-    screen:expect([[
-      ~                        |
-      ~                        |
-      ~                        |
-      ~                        |
-      :set wildm               |
-      wildmenu  wildmode       |
-      :set wildm^               |
-    ]])
-    feed('<tab>') -- trigger wildmode full
-    screen:expect([[
-      ~                        |
-      ~                        |
-      ~                        |
-      :set wildm               |
-      wildmenu  wildmode       |
-      wildmenu  wildmode       |
-      :set wildmenu^            |
-    ]])
-    feed('<Esc>')
-    screen:expect([[
-      ^                         |
-      ~                        |
-      ~                        |
-      ~                        |
-      ~                        |
-      ~                        |
-                               |
-    ]])
-  end)
-
   it('wildmode=longest,list', function()
     -- Need more than 5 rows, else tabline is covered and will be redrawn.
     screen:try_resize(25, 7)
@@ -365,7 +326,6 @@ describe("'wildmenu'", function()
     screen:try_resize(25, 7)
 
     command('set laststatus=2')
-    command('set display+=msgsep')
     feed(':set wildm')
     feed('<c-d>')
     screen:expect([[