fix(prompt): emit change event for prompt newline (#28260)

Co-authored-by: Ilia Choly <ilia.choly@gmail.com>

src/nvim/eval.c

@@ -17,6 +17,7 @@
 #include "nvim/autocmd.h"
 #include "nvim/buffer.h"
 #include "nvim/buffer_defs.h"
+#include "nvim/change.h"
 #include "nvim/channel.h"
 #include "nvim/charset.h"
 #include "nvim/cmdexpand_defs.h"
@@ -8905,6 +8906,7 @@ void invoke_prompt_callback(void)
   // Add a new line for the prompt before invoking the callback, so that
   // text can always be inserted above the last line.
   ml_append(lnum, "", 0, false);
+  appended_lines_mark(lnum, 1);
   curwin->w_cursor.lnum = lnum + 1;
   curwin->w_cursor.col = 0;
 

test/functional/lua/buffer_updates_spec.lua

@@ -1266,6 +1266,25 @@ describe('lua: nvim_buf_attach on_bytes', function()
       }
     end)
 
+    it('prompt buffer', function()
+      local check_events = setup_eventcheck(verify, {})
+      api.nvim_set_option_value('buftype', 'prompt', {})
+      feed('i')
+      check_events {
+        { 'test1', 'bytes', 1, 3, 0, 0, 0, 0, 0, 0, 0, 2, 2 },
+      }
+      feed('<CR>')
+      check_events {
+        { 'test1', 'bytes', 1, 4, 1, 0, 3, 0, 0, 0, 1, 0, 1 },
+        { 'test1', 'bytes', 1, 5, 1, 0, 3, 0, 0, 0, 0, 2, 2 },
+      }
+      feed('<CR>')
+      check_events {
+        { 'test1', 'bytes', 1, 6, 2, 0, 6, 0, 0, 0, 1, 0, 1 },
+        { 'test1', 'bytes', 1, 7, 2, 0, 6, 0, 0, 0, 0, 2, 2 },
+      }
+    end)
+
     local function test_lockmarks(mode)
       local description = (mode ~= '') and mode or '(baseline)'
       it('test_lockmarks ' .. description .. ' %delete _', function()