feat(api/ui): win_extmarks

13 files changed, 332 insertions, 28 deletions

diff --git a/runtime/doc/api.txt b/runtime/doc/api.txt
index ed3a838b6d..ab6c6a8699 100644
--- a/runtime/doc/api.txt
+++ b/runtime/doc/api.txt
@@ -2706,6 +2706,11 @@ nvim_buf_set_extmark({buffer}, {ns_id}, {line}, {col}, {*opts})
                                 "hl_group" is used as highlight for the cchar
                                 if provided, otherwise it defaults to
                                 |hl-Conceal|.
+                              • ui_watched: boolean that indicates the mark
+                                should be drawn by a UI. When set, the UI will
+                                receive win_extmark events. Note: the mark is
+                                positioned by virt_text attributes. Can be
+                                used together with virt_text.
 
                 Return: ~
                     Id of the created/updated extmark
diff --git a/runtime/doc/ui.txt b/runtime/doc/ui.txt
index 8014199dc5..eb12fd38a0 100644
--- a/runtime/doc/ui.txt
+++ b/runtime/doc/ui.txt
@@ -627,6 +627,10 @@ tabs.
 	`botline` is set to one more than the line count of the buffer, if
 	there are filler lines past the end.
 
+["win_extmark", grid, win, ns_id, mark_id, row, col]
+	Updates the position of an extmark which is currently visible in a
+	window. Only emitted if the mark has the `ui_watched` attribute. 
+
 ==============================================================================
 Popupmenu Events						 *ui-popupmenu*
 
diff --git a/src/nvim/api/extmark.c b/src/nvim/api/extmark.c
index e408d88854..fa6923e6d5 100644
--- a/src/nvim/api/extmark.c
+++ b/src/nvim/api/extmark.c
@@ -146,6 +146,10 @@ static Array extmark_to_array(ExtmarkInfo extmark, bool id, bool add_dict)
           STRING_OBJ(cstr_to_string(virt_text_pos_str[decor->virt_text_pos])));
     }
 
+    if (decor->ui_watched) {
+      PUT(dict, "ui_watched", BOOLEAN_OBJ(true));
+    }
+
     if (kv_size(decor->virt_lines)) {
       Array all_chunks = ARRAY_DICT_INIT;
       bool virt_lines_leftcol = false;
@@ -170,7 +174,7 @@ static Array extmark_to_array(ExtmarkInfo extmark, bool id, bool add_dict)
       PUT(dict, "virt_lines_leftcol", BOOLEAN_OBJ(virt_lines_leftcol));
     }
 
-    if (decor->hl_id || kv_size(decor->virt_text)) {
+    if (decor->hl_id || kv_size(decor->virt_text) || decor->ui_watched) {
       PUT(dict, "priority", INTEGER_OBJ(decor->priority));
     }
 
@@ -472,6 +476,10 @@ Array nvim_buf_get_extmarks(Buffer buffer, Integer ns_id, Object start, Object e
 ///                   When a character is supplied it is used as |:syn-cchar|.
 ///                   "hl_group" is used as highlight for the cchar if provided,
 ///                   otherwise it defaults to |hl-Conceal|.
+///               - ui_watched: boolean that indicates the mark should be drawn
+///                   by a UI. When set, the UI will receive win_extmark events.
+///                   Note: the mark is positioned by virt_text attributes. Can be
+///                   used together with virt_text.
 ///
 /// @param[out]  err   Error details, if any
 /// @return Id of the created/updated extmark
@@ -709,6 +717,8 @@ Integer nvim_buf_set_extmark(Buffer buffer, Integer ns_id, Integer line, Integer
   bool ephemeral = false;
   OPTION_TO_BOOL(ephemeral, ephemeral, false);
 
+  OPTION_TO_BOOL(decor.ui_watched, ui_watched, false);
+
   if (line < 0) {
     api_set_error(err, kErrorTypeValidation, "line value outside range");
     goto error;
@@ -762,7 +772,7 @@ Integer nvim_buf_set_extmark(Buffer buffer, Integer ns_id, Integer line, Integer
 
   // TODO(bfredl): synergize these two branches even more
   if (ephemeral && decor_state.buf == buf) {
-    decor_add_ephemeral((int)line, (int)col, line2, col2, &decor);
+    decor_add_ephemeral((int)line, (int)col, line2, col2, &decor, (uint64_t)ns_id, id);
   } else {
     if (ephemeral) {
       api_set_error(err, kErrorTypeException, "not yet implemented");
diff --git a/src/nvim/api/keysets.lua b/src/nvim/api/keysets.lua
index 8ad4dae928..5baffaf505 100644
--- a/src/nvim/api/keysets.lua
+++ b/src/nvim/api/keysets.lua
@@ -28,6 +28,7 @@ return {
     "line_hl_group";
     "cursorline_hl_group";
     "conceal";
+    "ui_watched";
   };
   keymap = {
     "noremap";
diff --git a/src/nvim/api/ui.c b/src/nvim/api/ui.c
index d1b86ed328..4f9592bd52 100644
--- a/src/nvim/api/ui.c
+++ b/src/nvim/api/ui.c
@@ -810,3 +810,4 @@ static void remote_ui_inspect(UI *ui, Dictionary *info)
   UIData *data = ui->data;
   PUT(*info, "chan", INTEGER_OBJ((Integer)data->channel_id));
 }
+
diff --git a/src/nvim/api/ui.h b/src/nvim/api/ui.h
index b3af14f8a8..bc70406acb 100644
--- a/src/nvim/api/ui.h
+++ b/src/nvim/api/ui.h
@@ -4,6 +4,7 @@
 #include <stdint.h>
 
 #include "nvim/api/private/defs.h"
+#include "nvim/map.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "api/ui.h.generated.h"
diff --git a/src/nvim/api/ui_events.in.h b/src/nvim/api/ui_events.in.h
index db348359eb..63aaaae38a 100644
--- a/src/nvim/api/ui_events.in.h
+++ b/src/nvim/api/ui_events.in.h
@@ -123,6 +123,10 @@ void win_viewport(Integer grid, Window win, Integer topline,
                   Integer line_count)
   FUNC_API_SINCE(7) FUNC_API_REMOTE_ONLY;
 
+void win_extmark(Integer grid, Window win, Integer ns_id, Integer mark_id,
+                 Integer row, Integer col)
+  FUNC_API_SINCE(10) FUNC_API_REMOTE_ONLY;
+
 void popupmenu_show(Array items, Integer selected,
                     Integer row, Integer col, Integer grid)
   FUNC_API_SINCE(3) FUNC_API_REMOTE_ONLY;
diff --git a/src/nvim/decoration.c b/src/nvim/decoration.c
index c8f4b3e875..c6edf44c74 100644
--- a/src/nvim/decoration.c
+++ b/src/nvim/decoration.c
@@ -2,6 +2,7 @@
 // it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
 
 #include "nvim/buffer.h"
+#include "nvim/api/ui.h"
 #include "nvim/decoration.h"
 #include "nvim/extmark.h"
 #include "nvim/highlight.h"
@@ -73,7 +74,8 @@ void decor_redraw(buf_T *buf, int row1, int row2, Decoration *decor)
     }
   }
 
-  if (decor && kv_size(decor->virt_text)) {
+  if (decor && (kv_size(decor->virt_text)
+                || decor->ui_watched)) {
     redraw_buf_line_later(buf, row1 + 1);
   }
 
@@ -195,9 +197,11 @@ bool decor_redraw_start(buf_T *buf, int top_row, DecorState *state)
     Decoration decor = get_decor(mark);
 
     // Exclude non-paired marks unless they contain virt_text or a sign
+    // or they are ui-watched
     if (!mt_paired(mark)
         && !kv_size(decor.virt_text)
-        && !decor_has_sign(&decor)) {
+        && !decor_has_sign(&decor)
+        && !decor.ui_watched) {
       goto next_mark;
     }
 
@@ -206,21 +210,22 @@ bool decor_redraw_start(buf_T *buf, int top_row, DecorState *state)
     // Exclude start marks if the end mark position is above the top row
     // Exclude end marks if we have already added the start mark
     if ((mt_start(mark) && altpos.row < top_row
-         && !kv_size(decor.virt_text))
+         && !kv_size(decor.virt_text)
+         && !decor.ui_watched)
         || (mt_end(mark) && altpos.row >= top_row)) {
       goto next_mark;
     }
 
     if (mt_end(mark)) {
       decor_add(state, altpos.row, altpos.col, mark.pos.row, mark.pos.col,
-                &decor, false);
+                &decor, false, mark.ns, mark.id);
     } else {
       if (altpos.row == -1) {
         altpos.row = mark.pos.row;
         altpos.col = mark.pos.col;
       }
       decor_add(state, mark.pos.row, mark.pos.col, altpos.row, altpos.col,
-                &decor, false);
+                &decor, false, mark.ns, mark.id);
     }
 
 next_mark:
@@ -246,13 +251,13 @@ bool decor_redraw_line(buf_T *buf, int row, DecorState *state)
 }
 
 static void decor_add(DecorState *state, int start_row, int start_col, int end_row, int end_col,
-                      Decoration *decor, bool owned)
+                      Decoration *decor, bool owned, uint64_t ns_id, uint64_t mark_id)
 {
   int attr_id = decor->hl_id > 0 ? syn_id2attr(decor->hl_id) : 0;
 
   DecorRange range = { start_row, start_col, end_row, end_col,
                        *decor, attr_id,
-                       kv_size(decor->virt_text) && owned, -1 };
+                       kv_size(decor->virt_text) && owned, -1, ns_id, mark_id };
 
   kv_pushp(state->active);
   size_t index;
@@ -298,13 +303,13 @@ int decor_redraw_col(buf_T *buf, int col, int win_col, bool hidden, DecorState *
 
     if (endpos.row < mark.pos.row
         || (endpos.row == mark.pos.row && endpos.col <= mark.pos.col)) {
-      if (!kv_size(decor.virt_text)) {
+      if (!kv_size(decor.virt_text) && !decor.ui_watched) {
         goto next_mark;
       }
     }
 
     decor_add(state, mark.pos.row, mark.pos.col, endpos.row, endpos.col,
-              &decor, false);
+              &decor, false, mark.ns, mark.id);
 
 next_mark:
     marktree_itr_next(buf->b_marktree, state->itr);
@@ -321,7 +326,8 @@ next_mark:
     bool active = false, keep = true;
     if (item.end_row < state->row
         || (item.end_row == state->row && item.end_col <= col)) {
-      if (!(item.start_row >= state->row && kv_size(item.decor.virt_text))) {
+      if (!(item.start_row >= state->row
+            && (kv_size(item.decor.virt_text) || item.decor.ui_watched))) {
         keep = false;
       }
     } else {
@@ -349,7 +355,7 @@ next_mark:
       }
     }
     if ((item.start_row == state->row && item.start_col <= col)
-        && kv_size(item.decor.virt_text)
+        && (kv_size(item.decor.virt_text) || item.decor.ui_watched)
         && item.decor.virt_text_pos == kVTOverlay && item.win_col == -1) {
       item.win_col = (item.decor.virt_text_hide && hidden) ? -2 : win_col;
     }
@@ -517,7 +523,8 @@ bool decor_redraw_eol(buf_T *buf, DecorState *state, int *eol_attr, int eol_col)
   bool has_virttext = false;
   for (size_t i = 0; i < kv_size(state->active); i++) {
     DecorRange item = kv_A(state->active, i);
-    if (item.start_row == state->row && kv_size(item.decor.virt_text)) {
+    if (item.start_row == state->row
+        && (kv_size(item.decor.virt_text) || item.decor.ui_watched)) {
       has_virttext = true;
     }
 
@@ -528,13 +535,14 @@ bool decor_redraw_eol(buf_T *buf, DecorState *state, int *eol_attr, int eol_col)
   return has_virttext;
 }
 
-void decor_add_ephemeral(int start_row, int start_col, int end_row, int end_col, Decoration *decor)
+void decor_add_ephemeral(int start_row, int start_col, int end_row, int end_col,
+                         Decoration *decor, uint64_t ns_id, uint64_t mark_id)
 {
   if (end_row == -1) {
     end_row = start_row;
     end_col = start_col;
   }
-  decor_add(&decor_state, start_row, start_col, end_row, end_col, decor, true);
+  decor_add(&decor_state, start_row, start_col, end_row, end_col, decor, true, ns_id, mark_id);
 }
 
 
diff --git a/src/nvim/decoration.h b/src/nvim/decoration.h
index 97ab218f86..9a82af8661 100644
--- a/src/nvim/decoration.h
+++ b/src/nvim/decoration.h
@@ -60,10 +60,11 @@ struct Decoration {
   // TODO(bfredl): in principle this should be a schar_T, but we
   // probably want some kind of glyph cache for that..
   int conceal_char;
+  bool ui_watched;  // watched for win_extmark
 };
 #define DECORATION_INIT { KV_INITIAL_VALUE, KV_INITIAL_VALUE, 0, kVTEndOfLine, \
                           kHlModeUnknown, false, false, false, false, DECOR_PRIORITY_BASE, \
-                          0, 0, NULL, 0, 0, 0, 0, 0 }
+                          0, 0, NULL, 0, 0, 0, 0, 0, false }
 
 typedef struct {
   int start_row;
@@ -74,6 +75,8 @@ typedef struct {
   int attr_id;  // cached lookup of decor.hl_id
   bool virt_text_owned;
   int win_col;
+  uint64_t ns_id;
+  uint64_t mark_id;
 } DecorRange;
 
 typedef struct {
diff --git a/src/nvim/extmark.c b/src/nvim/extmark.c
index ffd68926f1..1b0e2c8590 100644
--- a/src/nvim/extmark.c
+++ b/src/nvim/extmark.c
@@ -69,7 +69,8 @@ void extmark_set(buf_T *buf, uint32_t ns_id, uint32_t *idp, int row, colnr_T col
   if (decor) {
     if (kv_size(decor->virt_text)
         || kv_size(decor->virt_lines)
-        || decor_has_sign(decor)) {
+        || decor_has_sign(decor)
+        || decor->ui_watched) {
       decor_full = true;
       decor = xmemdup(decor, sizeof *decor);
     }
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index 58abc1599a..2c3f8f307b 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -67,6 +67,7 @@
 
 #include "nvim/api/extmark.h"
 #include "nvim/api/private/helpers.h"
+#include "nvim/api/ui.h"
 #include "nvim/api/vim.h"
 #include "nvim/arabic.h"
 #include "nvim/ascii.h"
@@ -161,6 +162,14 @@ static bool msg_grid_invalid = false;
 
 static bool resizing = false;
 
+typedef struct {
+  NS ns_id;
+  uint64_t mark_id;
+  int win_row;
+  int win_col;
+} WinExtmark;
+static kvec_t(WinExtmark) win_extmark_arr INIT(= KV_INITIAL_VALUE);
+
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "screen.c.generated.h"
@@ -1314,6 +1323,8 @@ static void win_update(win_T *wp, DecorProviders *providers)
   srow = 0;
   lnum = wp->w_topline;  // first line shown in window
 
+  win_extmark_arr.size = 0;
+
   decor_redraw_reset(buf, &decor_state);
 
   DecorProviders line_providers;
@@ -1692,6 +1703,16 @@ static void win_update(win_T *wp, DecorProviders *providers)
   wp->w_old_topfill = wp->w_topfill;
   wp->w_old_botfill = wp->w_botfill;
 
+  // Send win_extmarks if needed
+  if (kv_size(win_extmark_arr) > 0) {
+    for (size_t n = 0; n < kv_size(win_extmark_arr); n++) {
+      ui_call_win_extmark(
+          wp->w_grid_alloc.handle, wp->handle,
+          kv_A(win_extmark_arr, n).ns_id, kv_A(win_extmark_arr, n).mark_id,
+          kv_A(win_extmark_arr, n).win_row, kv_A(win_extmark_arr, n).win_col);
+    }
+  }
+
   if (dollar_vcol == -1) {
     /*
      * There is a trick with w_botline.  If we invalidate it on each
@@ -1964,7 +1985,7 @@ static inline void provider_err_virt_text(linenr_T lnum, char *err)
           ((VirtTextChunk){ .text = provider_err,
                             .hl_id = hl_err }));
   err_decor.virt_text_width = mb_string2cells((char_u *)err);
-  decor_add_ephemeral(lnum - 1, 0, lnum - 1, 0, &err_decor);
+  decor_add_ephemeral(lnum - 1, 0, lnum - 1, 0, &err_decor, 0, 0);
 }
 
 static inline void get_line_number_str(win_T *wp, linenr_T lnum, char_u *buf, size_t buf_len)
@@ -2881,7 +2902,7 @@ static int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool noc
           && vcol >= (long)wp->w_virtcol)
          || (number_only && draw_state > WL_NR))
         && filler_todo <= 0) {
-      draw_virt_text(buf, win_col_offset, &col, grid->Columns);
+      draw_virt_text(wp, buf, win_col_offset, &col, grid->Columns, row);
       grid_put_linebuf(grid, row, 0, col, -grid->Columns, wp->w_p_rl, wp,
                        wp->w_hl_attr_normal, false);
       // Pretend we have finished updating the window.  Except when
@@ -3951,7 +3972,7 @@ static int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool noc
         }
       }
 
-      draw_virt_text(buf, win_col_offset, &col, grid->Columns);
+      draw_virt_text(wp, buf, win_col_offset, &col, grid->Columns, row);
       grid_put_linebuf(grid, row, 0, col, grid->Columns, wp->w_p_rl, wp,
                        wp->w_hl_attr_normal, false);
       row++;
@@ -4195,7 +4216,7 @@ static int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool noc
                               kHlModeReplace, grid->Columns, offset);
         }
       } else {
-        draw_virt_text(buf, win_col_offset, &draw_col, grid->Columns);
+        draw_virt_text(wp, buf, win_col_offset, &draw_col, grid->Columns, row);
       }
 
       grid_put_linebuf(grid, row, 0, draw_col, grid->Columns, wp->w_p_rl,
@@ -4274,14 +4295,15 @@ static int win_line(win_T *wp, linenr_T lnum, int startrow, int endrow, bool noc
   return row;
 }
 
-void draw_virt_text(buf_T *buf, int col_off, int *end_col, int max_col)
+void draw_virt_text(win_T *wp, buf_T *buf, int col_off, int *end_col, int max_col, int win_row)
 {
   DecorState *state = &decor_state;
   int right_pos = max_col;
   bool do_eol = state->eol_col > -1;
   for (size_t i = 0; i < kv_size(state->active); i++) {
     DecorRange *item = &kv_A(state->active, i);
-    if (!(item->start_row == state->row && kv_size(item->decor.virt_text))) {
+    if (!(item->start_row == state->row
+          && (kv_size(item->decor.virt_text) || item->decor.ui_watched))) {
       continue;
     }
     if (item->win_col == -1) {
@@ -4297,9 +4319,17 @@ void draw_virt_text(buf_T *buf, int col_off, int *end_col, int max_col)
     if (item->win_col < 0) {
       continue;
     }
-
-    int col = draw_virt_text_item(buf, item->win_col, item->decor.virt_text,
-                                  item->decor.hl_mode, max_col, item->win_col - col_off);
+    int col;
+    if (item->decor.ui_watched) {
+      // send mark position to UI
+      col = item->win_col;
+      WinExtmark m = { item->ns_id, item->mark_id, win_row, col };
+      kv_push(win_extmark_arr, m);
+    }
+    if (kv_size(item->decor.virt_text)) {
+      col = draw_virt_text_item(buf, item->win_col, item->decor.virt_text,
+                                item->decor.hl_mode, max_col, item->win_col - col_off);
+    }
     item->win_col = -2;  // deactivate
     if (item->decor.virt_text_pos == kVTEndOfLine && do_eol) {
       state->eol_col = col + 1;
diff --git a/test/functional/api/extmark_spec.lua b/test/functional/api/extmark_spec.lua
index e298eb3582..bc8d811c6d 100644
--- a/test/functional/api/extmark_spec.lua
+++ b/test/functional/api/extmark_spec.lua
@@ -1606,3 +1606,209 @@ describe('Extmarks buffer api with many marks', function()
     eq({}, get_marks(ns2))
   end)
 end)
+
+describe('API/win_extmark', function()
+  local screen
+  local marks, line1, line2
+  local ns
+
+  before_each(function()
+    -- Initialize some namespaces and insert text into a buffer
+    marks = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}
+
+    line1 = "non ui-watched line"
+    line2 = "ui-watched line"
+
+    clear()
+
+    insert(line1)
+    feed("o<esc>")
+    insert(line2)
+    ns = request('nvim_create_namespace', "extmark-ui")
+  end)
+
+  it('sends and only sends ui-watched marks to ui', function()
+    screen = Screen.new(20, 4)
+    screen:attach()
+    -- should send this
+    set_extmark(ns, marks[1], 1, 0, { ui_watched = true })
+    -- should not send this
+    set_extmark(ns, marks[2], 0, 0, { ui_watched = false })
+    screen:expect({
+      grid = [[
+      non ui-watched line |
+      ui-watched lin^e     |
+      ~                   |
+                          |
+    ]],
+      extmarks = {
+        [2] = {
+          -- positioned at the end of the 2nd line
+          { {id = 1000}, 1, 1, 1, 16 },
+        }
+      },
+    })
+  end)
+
+  it('sends multiple ui-watched marks to ui', function()
+    screen = Screen.new(20, 4)
+    screen:attach()
+    -- should send all of these
+    set_extmark(ns, marks[1], 1, 0, { ui_watched = true, virt_text_pos = "overlay" })
+    set_extmark(ns, marks[2], 1, 2, { ui_watched = true, virt_text_pos = "overlay" })
+    set_extmark(ns, marks[3], 1, 4, { ui_watched = true, virt_text_pos = "overlay" })
+    set_extmark(ns, marks[4], 1, 6, { ui_watched = true, virt_text_pos = "overlay" })
+    set_extmark(ns, marks[5], 1, 8, { ui_watched = true })
+    screen:expect({
+      grid = [[
+      non ui-watched line |
+      ui-watched lin^e     |
+      ~                   |
+                          |
+    ]],
+      extmarks = {
+        [2] = {
+          -- earlier notifications
+          { {id = 1000}, 1, 1, 1, 0 },
+          { {id = 1000}, 1, 1, 1, 0 }, { {id = 1000}, 1, 2, 1, 2 },
+          { {id = 1000}, 1, 1, 1, 0 }, { {id = 1000}, 1, 2, 1, 2 }, { {id = 1000}, 1, 3, 1, 4 },
+          { {id = 1000}, 1, 1, 1, 0 }, { {id = 1000}, 1, 2, 1, 2 }, { {id = 1000}, 1, 3, 1, 4 }, { {id = 1000}, 1, 4, 1, 6 },
+          -- final
+          --   overlay
+          { {id = 1000}, 1, 1, 1, 0 },
+          { {id = 1000}, 1, 2, 1, 2 },
+          { {id = 1000}, 1, 3, 1, 4 },
+          { {id = 1000}, 1, 4, 1, 6 },
+          --   eol
+          { {id = 1000}, 1, 5, 1, 16 },
+        }
+      },
+    })
+  end)
+
+  it('updates ui-watched marks', function()
+    screen = Screen.new(20, 4)
+    screen:attach()
+    -- should send this
+    set_extmark(ns, marks[1], 1, 0, { ui_watched = true })
+    -- should not send this
+    set_extmark(ns, marks[2], 0, 0, { ui_watched = false })
+    -- make some changes
+    insert(" update")
+    screen:expect({
+      grid = [[
+      non ui-watched line |
+      ui-watched linupdat^e|
+      e                   |
+                          |
+    ]],
+      extmarks = {
+        [2] = {
+          -- positioned at the end of the 2nd line
+          { {id = 1000}, 1, 1, 1, 16 },
+          -- updated and wrapped to 3rd line
+          { {id = 1000}, 1, 1, 2, 2 },
+        }
+      }
+    })
+    feed("<c-e>")
+    screen:expect({
+      grid = [[
+      ui-watched linupdat^e|
+      e                   |
+      ~                   |
+                          |
+    ]],
+      extmarks = {
+        [2] = {
+          -- positioned at the end of the 2nd line
+          { {id = 1000}, 1, 1, 1, 16 },
+          -- updated and wrapped to 3rd line
+          { {id = 1000}, 1, 1, 2, 2 },
+          -- scrolled up one line, should be handled by grid scroll
+        }
+      }
+    })
+  end)
+
+  it('sends ui-watched to splits', function()
+    screen = Screen.new(20, 8)
+    screen:attach({ext_multigrid=true})
+    -- should send this
+    set_extmark(ns, marks[1], 1, 0, { ui_watched = true })
+    -- should not send this
+    set_extmark(ns, marks[2], 0, 0, { ui_watched = false })
+    command('split')
+    screen:expect({
+      grid = [[
+        ## grid 1
+          [4:--------------------]|
+          [4:--------------------]|
+          [4:--------------------]|
+          [No Name] [+]       |
+          [2:--------------------]|
+          [2:--------------------]|
+          [No Name] [+]       |
+          [3:--------------------]|
+        ## grid 2
+          non ui-watched line |
+          ui-watched line     |
+        ## grid 3
+                              |
+        ## grid 4
+          non ui-watched line |
+          ui-watched lin^e     |
+          ~                   |
+    ]],
+      extmarks = {
+        [2] = {
+          -- positioned at the end of the 2nd line
+          { {id = 1000}, 1, 1, 1, 16 },
+          -- updated after split
+          { {id = 1000}, 1, 1, 1, 16 },
+        },
+        [4] = {
+          -- only after split
+          { {id = 1001}, 1, 1, 1, 16 },
+        }
+      }
+    })
+    -- make some changes
+    insert(" update")
+    screen:expect({
+      grid = [[
+        ## grid 1
+          [4:--------------------]|
+          [4:--------------------]|
+          [4:--------------------]|
+          [No Name] [+]       |
+          [2:--------------------]|
+          [2:--------------------]|
+          [No Name] [+]       |
+          [3:--------------------]|
+        ## grid 2
+          non ui-watched line |
+          ui-watched linupd@@@|
+        ## grid 3
+                              |
+        ## grid 4
+          non ui-watched line |
+          ui-watched linupdat^e|
+          e                   |
+    ]],
+      extmarks = {
+        [2] = {
+          -- positioned at the end of the 2nd line
+          { {id = 1000}, 1, 1, 1, 16 },
+          -- updated after split
+          { {id = 1000}, 1, 1, 1, 16 },
+        },
+        [4] = {
+          { {id = 1001}, 1, 1, 1, 16 },
+          -- updated
+          { {id = 1001}, 1, 1, 2, 2 },
+        }
+      }
+    })
+  end)
+end)
diff --git a/test/functional/ui/screen.lua b/test/functional/ui/screen.lua
index e8a39ab6f8..b3d1abca69 100644
--- a/test/functional/ui/screen.lua
+++ b/test/functional/ui/screen.lua
@@ -179,6 +179,7 @@ function Screen.new(width, height)
     _width = width,
     _height = height,
     _grids = {},
+    _grid_win_extmarks = {},
     _cursor = {
       grid = 1, row = 1, col = 1
     },
@@ -278,6 +279,8 @@ local ext_keys = {
 --              attributes in the final state are an error.
 --              Use screen:set_default_attr_ids() to define attributes for many
 --              expect() calls.
+-- extmarks:    Expected win_extmarks accumulated for the grids. For each grid,
+--              the win_extmark messages are accumulated into an array.
 -- condition:   Function asserting some arbitrary condition. Return value is
 --              ignored, throw an error (use eq() or similar) to signal failure.
 -- any:         Lua pattern string expected to match a screen line. NB: the
@@ -320,7 +323,7 @@ function Screen:expect(expected, attr_ids, ...)
     assert(not (attr_ids ~= nil))
     local is_key = {grid=true, attr_ids=true, condition=true, mouse_enabled=true,
                     any=true, mode=true, unchanged=true, intermediate=true,
-                    reset=true, timeout=true, request_cb=true, hl_groups=true}
+                    reset=true, timeout=true, request_cb=true, hl_groups=true, extmarks=true}
     for _, v in ipairs(ext_keys) do
       is_key[v] = true
     end
@@ -459,6 +462,25 @@ screen:redraw_debug() to show all intermediate screen states.  ]])
         end
       end
     end
+
+    if expected.extmarks ~= nil then
+      for gridid, expected_marks in pairs(expected.extmarks) do
+        local stored_marks = self._grid_win_extmarks[gridid]
+        if stored_marks == nil then
+          return 'no win_extmark for grid '..tostring(gridid)
+        end
+        local status, res = pcall(eq, expected_marks, stored_marks, "extmarks for grid "..tostring(gridid))
+        if not status then
+          return tostring(res)
+        end
+      end
+      for gridid, _ in pairs(self._grid_win_extmarks) do
+        local expected_marks = expected.extmarks[gridid]
+        if expected_marks == nil then
+          return 'unexpected win_extmark for grid '..tostring(gridid)
+        end
+      end
+    end
   end, expected)
 end
 
@@ -703,6 +725,7 @@ function Screen:_reset()
   self.cmdline_block = {}
   self.wildmenu_items = nil
   self.wildmenu_pos = nil
+  self._grid_win_extmarks = {}
 end
 
 function Screen:_handle_mode_info_set(cursor_style_enabled, mode_info)
@@ -803,6 +826,13 @@ function Screen:_handle_win_close(grid)
   self.float_pos[grid] = nil
 end
 
+function Screen:_handle_win_extmark(grid, ...)
+  if self._grid_win_extmarks[grid] == nil then
+    self._grid_win_extmarks[grid] = {}
+  end
+  table.insert(self._grid_win_extmarks[grid], {...})
+end
+
 function Screen:_handle_busy_start()
   self._busy = true
 end