API/buffer-updates: always detach on buf-reload #9643

Independently of the 'undoreload' option and the length of the file.
closes #9642
closes #9643

src/nvim/buffer.c

@@ -591,7 +591,8 @@ void close_buffer(win_T *win, buf_T *buf, int action, int abort_if_last)
   /* Change directories when the 'acd' option is set. */
   do_autochdir();
 
-  // disable buffer updates for the current buffer
+  // Disable buffer-updates for the current buffer.
+  // No need to check `unload_buf`: in that case the function returned above.
   buf_updates_unregister_all(buf);
 
   /*

src/nvim/ex_cmds.c

@@ -2476,8 +2476,8 @@ int do_ecmd(
     }
     set_bufref(&bufref, buf);
     if (p_ur < 0 || curbuf->b_ml.ml_line_count <= p_ur) {
-      /* Save all the text, so that the reload can be undone.
+      // Save all the text, so that the reload can be undone.
-       * Sync first so that this is a separate undo-able action. */
+      // Sync first so that this is a separate undo-able action.
       u_sync(false);
       if (u_savecommon(0, curbuf->b_ml.ml_line_count + 1, 0, true)
           == FAIL) {
@@ -2491,6 +2491,7 @@ int do_ecmd(
       // Tell readfile() not to clear or reload undo info.
       readfile_flags = READ_KEEP_UNDO;
     } else {
+      buf_updates_unregister_all(curbuf);
       buf_freeall(curbuf, 0);  // Free all things for buffer.
     }
     // If autocommands deleted the buffer we were going to re-edit, give

test/functional/api/buffer_updates_spec.lua

@@ -678,6 +678,32 @@ describe('API: buffer events:', function()
     expectn('Hello There', {})
   end)
 
+  it(':edit! (reload) causes detach #9642', function()
+    local b, tick = editoriginal(true, {'AAA', 'BBB'})
+    command('set undoreload=1')
+
+    command('normal! x')
+    tick = tick + 1
+    expectn('nvim_buf_lines_event', {b, tick, 0, 1, {'AA'}, false})
+
+    command('edit!')
+    expectn('nvim_buf_detach_event', {b})
+  end)
+
+  it(':enew! does not detach hidden buffer', function()
+    local b, tick = editoriginal(true, {'AAA', 'BBB'})
+    local channel = nvim('get_api_info')[1]
+
+    command('set undoreload=1 hidden')
+    command('normal! x')
+    tick = tick + 1
+    expectn('nvim_buf_lines_event', {b, tick, 0, 1, {'AA'}, false})
+
+    command('enew!')
+    eval('rpcnotify('..channel..', "Hello There")')
+    expectn('Hello There', {})
+  end)
+
   it('stays attached if the buffer is hidden', function()
     local b, tick = editoriginal(true, {'AAA'})
     local channel = nvim('get_api_info')[1]