feat(api)!: nvim_open_win: noautocmd blocks all autocmds #28192

Problem: noautocmd is confusing; despite its name, it doesn't block all
autocommands (instead it blocks only those related to setting the buffer), and
is commonly used by plugins to open windows while producing minimal
side-effects.

Solution: be consistent and block all autocommands when noautocmd is set.
This includes WinNew (again), plus autocommands from entering the window (if
enter is set) like WinEnter, WinLeave, TabEnter, .etc.

See the discussion at https://github.com/neovim/neovim/pull/14659#issuecomment-2040029517
for more information.

Remove win_set_buf's noautocmd argument, as it's no longer needed.

NOTE: pum_create_float_preview sets noautocmd for win_set_buf, but all its
callers already use block_autocmds.

Despite that, pum_create_float_preview doesn't actually properly handle
autocommands (it has no checks for whether those from win_enter or
nvim_create_buf free the window).

For now, ensure autocommands are blocked within it for correctness (in case it's
ever called outside of a block_autocmds context; the function seems to have been
refactored in #26739 anyway).

src/nvim/api/win_config.c

@@ -199,9 +199,8 @@
 ///   - footer_pos: Footer position. Must be set with `footer` option.
 ///     Value can be one of "left", "center", or "right".
 ///     Default is `"left"`.
-///   - noautocmd: If true then autocommands triggered from setting the
-///     `buffer` to display are blocked (e.g: |BufEnter|, |BufLeave|,
-///     |BufWinEnter|).
+///   - noautocmd: If true then all autocommands are blocked for the duration of
+///     the call.
 ///   - fixed: If true when anchor is NW or SW, the float window
 ///            would be kept fixed even if the window would be truncated.
 ///   - hide: If true the floating window will be hidden.
@@ -230,6 +229,10 @@ Window nvim_open_win(Buffer buffer, Boolean enter, Dict(win_config) *config, Err
   }
 
   bool is_split = HAS_KEY_X(config, split) || HAS_KEY_X(config, vertical);
+  Window rv = 0;
+  if (fconfig.noautocmd) {
+    block_autocmds();
+  }
 
   win_T *wp = NULL;
   tabpage_T *tp = curtab;
@@ -239,15 +242,15 @@ Window nvim_open_win(Buffer buffer, Boolean enter, Dict(win_config) *config, Err
       parent = find_window_by_handle(fconfig.window, err);
       if (!parent) {
         // find_window_by_handle has already set the error
-        return 0;
+        goto cleanup;
       } else if (parent->w_floating) {
         api_set_error(err, kErrorTypeException, "Cannot split a floating window");
-        return 0;
+        goto cleanup;
       }
     }
 
     if (!check_split_disallowed_err(parent ? parent : curwin, err)) {
-      return 0;  // error already set
+      goto cleanup;  // error already set
     }
 
     if (HAS_KEY_X(config, vertical) && !HAS_KEY_X(config, split)) {
@@ -283,7 +286,7 @@ Window nvim_open_win(Buffer buffer, Boolean enter, Dict(win_config) *config, Err
     if (!ERROR_SET(err)) {
       api_set_error(err, kErrorTypeException, "Failed to create window");
     }
-    return 0;
+    goto cleanup;
   }
 
   // Autocommands may close `wp` or move it to another tabpage, so update and check `tp` after each
@@ -291,8 +294,8 @@ Window nvim_open_win(Buffer buffer, Boolean enter, Dict(win_config) *config, Err
   // Also, autocommands may free the `buf` to switch to, so store a bufref to check.
   bufref_T bufref;
   set_bufref(&bufref, buf);
-  switchwin_T switchwin;
-  {
+  if (!fconfig.noautocmd) {
+    switchwin_T switchwin;
     const int result = switch_win_noblock(&switchwin, wp, tp, true);
     assert(result == OK);
     (void)result;
@@ -313,7 +316,7 @@ Window nvim_open_win(Buffer buffer, Boolean enter, Dict(win_config) *config, Err
       autocmd_no_enter++;
       autocmd_no_leave++;
     }
-    win_set_buf(wp, buf, fconfig.noautocmd, err);
+    win_set_buf(wp, buf, err);
     if (!fconfig.noautocmd) {
       tp = win_find_tabpage(wp);
     }
@@ -324,14 +327,20 @@ Window nvim_open_win(Buffer buffer, Boolean enter, Dict(win_config) *config, Err
   }
   if (!tp) {
     api_set_error(err, kErrorTypeException, "Window was closed immediately");
-    return 0;
+    goto cleanup;
   }
 
   if (fconfig.style == kWinStyleMinimal) {
     win_set_minimal_style(wp);
     didset_window_options(wp, true);
   }
-  return wp->handle;
+  rv = wp->handle;
+
+cleanup:
+  if (fconfig.noautocmd) {
+    unblock_autocmds();
+  }
+  return rv;
 #undef HAS_KEY_X
 }
 

src/nvim/api/window.c

@@ -71,7 +71,7 @@ void nvim_win_set_buf(Window window, Buffer buffer, Error *err)
     api_set_error(err, kErrorTypeException, "%s", e_cmdwin);
     return;
   }
-  win_set_buf(win, buf, false, err);
+  win_set_buf(win, buf, err);
 }
 
 /// Gets the (1,0)-indexed, buffer-relative cursor position for a given window