UIEnter/UILeave: fire for embedder UI, builtin TUI

Before this, --embed UIs (without --headless) would not trigger UIEnter.

For TUI, maybe UIEnter isn't useful, but:
- It is less "surprising"/special.
- Makes documentation simpler.
- When TUI becomes a coprocess, it will happen anyway.

src/nvim/main.c

@@ -12,6 +12,7 @@
 #include "nvim/ascii.h"
 #include "nvim/vim.h"
 #include "nvim/main.h"
+#include "nvim/aucmd.h"
 #include "nvim/buffer.h"
 #include "nvim/charset.h"
 #include "nvim/diff.h"
@@ -351,7 +352,7 @@ int main(int argc, char **argv)
   bool use_remote_ui = (embedded_mode && !headless_mode);
   bool use_builtin_ui = (!headless_mode && !embedded_mode && !silent_mode);
   if (use_remote_ui || use_builtin_ui) {
-    TIME_MSG("waiting for UI to make request");
+    TIME_MSG("waiting for UI");
     if (use_remote_ui) {
       remote_ui_wait_for_attach();
     } else {
@@ -537,6 +538,10 @@ int main(int argc, char **argv)
   set_vim_var_nr(VV_VIM_DID_ENTER, 1L);
   apply_autocmds(EVENT_VIMENTER, NULL, NULL, false, curbuf);
   TIME_MSG("VimEnter autocommands");
+  if (use_remote_ui || use_builtin_ui) {
+    do_autocmd_uienter(use_remote_ui ? CHAN_STDIO : 0, true);
+    TIME_MSG("UIEnter autocommands");
+  }
 
   // Adjust default register name for "unnamed" in 'clipboard'. Can only be
   // done after the clipboard is available and all initial commands that may

test/functional/api/ui_spec.lua

@@ -37,7 +37,9 @@ describe('nvim_ui_attach()', function()
 end)
 
 it('autocmds UIEnter/UILeave', function()
-  clear{args={
+  clear{
+    args_rm={'--headless'},
+    args={
       '--cmd', 'let g:evs = []',
       '--cmd', 'autocmd UIEnter * :call add(g:evs, "UIEnter") | let g:uienter_ev = deepcopy(v:event)',
       '--cmd', 'autocmd UILeave * :call add(g:evs, "UILeave") | let g:uileave_ev = deepcopy(v:event)',

test/functional/terminal/tui_spec.lua

@@ -767,11 +767,36 @@ describe('TUI', function()
   end)
 end)
 
+describe('TUI UIEnter/UILeave', function()
+  it('fires exactly once, after VimEnter', function()
+    clear()
+    local screen = thelpers.screen_setup(0,
+      '["'..nvim_prog..'", "-u", "NONE", "-i", "NONE"'
+      ..[[, "--cmd", "set noswapfile noshowcmd noruler"]]
+      ..[[, "--cmd", "let g:evs = []"]]
+      ..[[, "--cmd", "autocmd UIEnter  * :call add(g:evs, 'UIEnter')"]]
+      ..[[, "--cmd", "autocmd UILeave  * :call add(g:evs, 'UILeave')"]]
+      ..[[, "--cmd", "autocmd VimEnter * :call add(g:evs, 'VimEnter')"]]
+      ..']'
+    )
+    feed_data(":echo g:evs\n")
+    screen:expect{grid=[[
+      {1: }                                                 |
+      {4:~                                                 }|
+      {4:~                                                 }|
+      {4:~                                                 }|
+      {5:[No Name]                                         }|
+      ['VimEnter', 'UIEnter']                           |
+      {3:-- TERMINAL --}                                    |
+    ]]}
+  end)
+end)
+
 describe('TUI FocusGained/FocusLost', function()
   local screen
 
   before_each(function()
-    helpers.clear()
+    clear()
     screen = thelpers.screen_setup(0, '["'..nvim_prog
       ..'", "-u", "NONE", "-i", "NONE", "--cmd", "set noswapfile noshowcmd noruler"]')
     feed_data(":autocmd FocusGained * echo 'gained'\n")