buffer updates: mark sorted region as changed.

NB: currently this invalidates all extmarks inside the region.
Later on within-line extmarks could be preserved

src/nvim/ex_cmds.c

@@ -629,6 +629,8 @@ void ex_sort(exarg_T *eap)
   if (sort_abort)
     goto sortend;
 
+  bcount_t old_count = 0, new_count = 0;
+
   // Insert the lines in the sorted order below the last one.
   lnum = eap->line2;
   for (i = 0; i < count; i++) {
@@ -641,6 +643,8 @@ void ex_sort(exarg_T *eap)
     }
 
     s = ml_get(get_lnum);
+    size_t bytelen = STRLEN(s) + 1;  // include EOL in bytelen
+    old_count += bytelen;
     if (!unique || i == 0
         || (sort_ic ? STRICMP(s, sortbuf1) : STRCMP(s, sortbuf1)) != 0) {
       // Copy the line into a buffer, it may become invalid in
@@ -649,6 +653,7 @@ void ex_sort(exarg_T *eap)
       if (ml_append(lnum++, sortbuf1, (colnr_T)0, false) == FAIL) {
         break;
       }
+      new_count += bytelen;
     }
     fast_breakcheck();
     if (got_int)
@@ -668,11 +673,16 @@ void ex_sort(exarg_T *eap)
   deleted = (long)(count - (lnum - eap->line2));
   if (deleted > 0) {
     mark_adjust(eap->line2 - deleted, eap->line2, (long)MAXLNUM, -deleted,
-                kExtmarkUndo);
+                kExtmarkNOOP);
     msgmore(-deleted);
   } else if (deleted < 0) {
-    mark_adjust(eap->line2, MAXLNUM, -deleted, 0L, kExtmarkUndo);
+    mark_adjust(eap->line2, MAXLNUM, -deleted, 0L, kExtmarkNOOP);
   }
+
+  extmark_splice(curbuf, eap->line1-1, 0,
+                 count, 0, old_count,
+                 lnum - eap->line2, 0, new_count, kExtmarkUndo);
+
   if (change_occurred || deleted != 0) {
     changed_lines(eap->line1, 0, eap->line2 + 1, -deleted, true);
   }

test/functional/treesitter/highlight_spec.lua

@@ -270,6 +270,81 @@ describe('treesitter highlighting', function()
     ]]}
   end)
 
+  it('is updated with :sort', function()
+    if pending_c_parser(pending) then return end
+
+    insert(test_text)
+    exec_lua [[
+      local parser = vim.treesitter.get_parser(0, "c")
+      test_hl = vim.treesitter.highlighter.new(parser, {queries = {c = hl_query}})
+    ]]
+    screen:expect{grid=[[
+        {3:int} width = {5:INT_MAX}, height = {5:INT_MAX};                         |
+        {3:bool} ext_widgets[kUIExtCount];                                 |
+        {4:for} ({3:UIExtension} i = {5:0}; ({3:int})i < kUIExtCount; i++) {           |
+          ext_widgets[i] = true;                                       |
+        }                                                              |
+                                                                       |
+        {3:bool} inclusive = ui_override();                                |
+        {4:for} ({3:size_t} i = {5:0}; i < ui_count; i++) {                        |
+          {3:UI} *ui = uis[i];                                             |
+          width = {5:MIN}(ui->width, width);                               |
+          height = {5:MIN}(ui->height, height);                            |
+          foo = {5:BAR}(ui->bazaar, bazaar);                               |
+          {4:for} ({3:UIExtension} j = {5:0}; ({3:int})j < kUIExtCount; j++) {         |
+            ext_widgets[j] &= (ui->ui_ext[j] || inclusive);            |
+          }                                                            |
+        }                                                              |
+      ^}                                                                |
+                                                                       |
+    ]]}
+
+    feed ":sort<cr>"
+    screen:expect{grid=[[
+      ^                                                                 |
+            ext_widgets[j] &= (ui->ui_ext[j] || inclusive);            |
+          {3:UI} *ui = uis[i];                                             |
+          ext_widgets[i] = true;                                       |
+          foo = {5:BAR}(ui->bazaar, bazaar);                               |
+          {4:for} ({3:UIExtension} j = {5:0}; ({3:int})j < kUIExtCount; j++) {         |
+          height = {5:MIN}(ui->height, height);                            |
+          width = {5:MIN}(ui->width, width);                               |
+          }                                                            |
+        {3:bool} ext_widgets[kUIExtCount];                                 |
+        {3:bool} inclusive = ui_override();                                |
+        {4:for} ({3:UIExtension} i = {5:0}; ({3:int})i < kUIExtCount; i++) {           |
+        {4:for} ({3:size_t} i = {5:0}; i < ui_count; i++) {                        |
+        {3:int} width = {5:INT_MAX}, height = {5:INT_MAX};                         |
+        }                                                              |
+        }                                                              |
+      {3:void} ui_refresh({3:void})                                            |
+      :sort                                                            |
+    ]]}
+
+    feed "u"
+
+    screen:expect{grid=[[
+        {3:int} width = {5:INT_MAX}, height = {5:INT_MAX};                         |
+        {3:bool} ext_widgets[kUIExtCount];                                 |
+        {4:for} ({3:UIExtension} i = {5:0}; ({3:int})i < kUIExtCount; i++) {           |
+          ext_widgets[i] = true;                                       |
+        }                                                              |
+                                                                       |
+        {3:bool} inclusive = ui_override();                                |
+        {4:for} ({3:size_t} i = {5:0}; i < ui_count; i++) {                        |
+          {3:UI} *ui = uis[i];                                             |
+          width = {5:MIN}(ui->width, width);                               |
+          height = {5:MIN}(ui->height, height);                            |
+          foo = {5:BAR}(ui->bazaar, bazaar);                               |
+          {4:for} ({3:UIExtension} j = {5:0}; ({3:int})j < kUIExtCount; j++) {         |
+            ext_widgets[j] &= (ui->ui_ext[j] || inclusive);            |
+          }                                                            |
+        }                                                              |
+      ^}                                                                |
+      19 changes; before #2  {MATCH:.*}|
+    ]]}
+  end)
+
   it("supports with custom parser", function()
     if pending_c_parser(pending) then return end