test(messages): skip os_delay during tests

Problem:
Tests that trigger `os_delay` messages may take 1-3 seconds, wasting
build/CI time, since this serves no purpose in tests.

Solution:
- Introduce `msg_delay` for cases where `os_delay` is being used as
  a "UI feature".
- Skip `msg_delay` in tests.

src/nvim/buffer.c

@@ -1992,7 +1992,7 @@ buf_T *buflist_new(char *ffname_arg, char *sfname_arg, linenr_T lnum, int flags)
       emsg(_("W14: Warning: List of file names overflow"));
       if (emsg_silent == 0 && !in_assert_fails && !ui_has(kUIMessages)) {
         ui_flush();
-        os_delay(3001, true);  // make sure it is noticed
+        msg_delay(3001, true);  // make sure it is noticed
       }
       top_file_num = 1;
     }

src/nvim/change.c

@@ -94,7 +94,7 @@ void change_warning(buf_T *buf, int col)
     msg_end();
     if (msg_silent == 0 && !silent_mode && ui_active() && !ui_has(kUIMessages)) {
       ui_flush();
-      os_delay(1002, true);  // give the user time to think about it
+      msg_delay(1002, true);  // give the user time to think about it
     }
     buf->b_did_warn = true;
     redraw_cmdline = false;  // don't redraw and erase the message
@@ -133,7 +133,7 @@ void changed(buf_T *buf)
       // and don't let the emsg() set msg_scroll.
       if (need_wait_return && emsg_silent == 0 && !in_assert_fails && !ui_has(kUIMessages)) {
         ui_flush();
-        os_delay(2002, true);
+        msg_delay(2002, true);
         wait_return(true);
         msg_scroll = save_msg_scroll;
       } else {

src/nvim/fileio.c

@@ -3030,7 +3030,7 @@ int buf_check_timestamp(buf_T *buf)
         if (emsg_silent == 0 && !in_assert_fails && !ui_has(kUIMessages)) {
           ui_flush();
           // give the user some time to think about it
-          os_delay(1004, true);
+          msg_delay(1004, true);
 
           // don't redraw and erase the message
           redraw_cmdline = false;

src/nvim/highlight_group.c

@@ -2393,6 +2393,7 @@ static void highlight_list_two(int cnt, int id)
   msg_puts_hl(&("N \bI \b!  \b"[cnt / 11]), id, false);
   msg_clr_eos();
   ui_flush();
+  // TODO(justinmk): is this delay needed? ":hi" seems to work without it.
   os_delay(cnt == 99 ? 40 : (uint64_t)cnt * 50, false);
 }
 

src/nvim/insexpand.c

@@ -554,7 +554,7 @@ bool check_compl_option(bool dict_opt)
       setcursor();
       if (!ui_has(kUIMessages)) {
         ui_flush();
-        os_delay(2004, false);
+        msg_delay(2004, false);
       }
     }
     return false;

src/nvim/main.c

@@ -154,6 +154,7 @@ static const char *err_extra_cmd =
 void event_init(void)
 {
   loop_init(&main_loop, NULL);
+  env_init();
   resize_events = multiqueue_new_child(main_loop.events);
 
   autocmd_init();

src/nvim/message.c

@@ -3923,6 +3923,20 @@ int vim_dialog_yesnoallcancel(int type, char *title, char *message, int dflt)
   return VIM_CANCEL;
 }
 
+/// Force the user to see a message by pausing for `ms` milliseconds.
+///
+/// TODO(justinmk): Most of these cases may not be needed after "ui2"...
+void msg_delay(uint64_t ms, bool ignoreinput)
+{
+  if (nvim_testing) {
+    // XXX: Skip non-functional (UI only) delay in tests/CI.
+    ms = 100;
+  }
+
+  DLOG("%" PRIu64 " ms%s", ms, nvim_testing ? " (skipped by NVIM_TEST)" : "");
+  os_delay(ms, ignoreinput);
+}
+
 /// Check if there should be a delay to allow the user to see a message.
 ///
 /// Used before clearing or redrawing the screen or the command line.
@@ -3931,7 +3945,7 @@ void msg_check_for_delay(bool check_msg_scroll)
   if ((emsg_on_display || (check_msg_scroll && msg_scroll))
       && !did_wait_return && emsg_silent == 0 && !in_assert_fails && !ui_has(kUIMessages)) {
     ui_flush();
-    os_delay(1006, true);
+    msg_delay(1006, true);
     emsg_on_display = false;
     if (check_msg_scroll) {
       msg_scroll = false;

src/nvim/normal.c

@@ -702,9 +702,10 @@ static void normal_redraw_mode_message(NormalState *s)
   ui_cursor_shape();                  // show different cursor shape
   ui_flush();
   if (!ui_has(kUIMessages) && (msg_scroll || emsg_on_display)) {
-    os_delay(1003, true);            // wait at least one second
+    msg_delay(1003, true);            // wait at least one second
   }
   if (ui_has(kUIMessages)) {
+    // TODO(justinmk): wtf is this delay for? From before 2014.
     os_delay(3003, false);           // wait up to three seconds
   }
   State = save_State;

src/nvim/os/env.c

@@ -57,6 +57,11 @@
 
 #include "os/env.c.generated.h"
 
+void env_init(void)
+{
+  nvim_testing = os_env_exists("NVIM_TEST", false);
+}
+
 /// Like getenv(), but returns NULL if the variable is empty.
 /// Result must be freed by the caller.
 /// @see os_env_exists

src/nvim/os/os.h

@@ -10,6 +10,9 @@
 #include "nvim/os/stdpaths_defs.h"
 #include "nvim/types_defs.h"
 
+// True if when running in a test environment ($NVIM_TEST).
+// TODO(justinmk): Can we use v:testing instead?
+EXTERN bool nvim_testing INIT( = false);
 extern char *default_vim_dir;
 extern char *default_vimruntime_dir;
 extern char *default_lib_dir;

src/nvim/tag.c

@@ -744,7 +744,7 @@ void do_tag(char *tag, int type, int count, int forceit, bool verbose)
         }
         if (ic && !msg_scrolled && msg_silent == 0 && !ui_has(kUIMessages)) {
           ui_flush();
-          os_delay(1007, true);
+          msg_delay(1007, true);
         }
       }
 
@@ -2983,7 +2983,7 @@ static int jumpto_tag(const char *lbuf_arg, int forceit, bool keep_help)
             msg(_("E435: Couldn't find tag, just guessing!"), 0);
             if (!msg_scrolled && msg_silent == 0 && !ui_has(kUIMessages)) {
               ui_flush();
-              os_delay(1010, true);
+              msg_delay(1010, true);
             }
           }
           retval = OK;

src/nvim/tui/tui.c

@@ -215,18 +215,14 @@ static void tui_set_term_mode(TUIData *tui, TermMode mode, bool set)
 void tui_handle_term_mode(TUIData *tui, TermMode mode, TermModeState state)
   FUNC_ATTR_NONNULL_ALL
 {
-  static TriState is_test = kNone;
-  if (is_test == kNone) {
-    // XXX: Skip some logs which are noisy in CI. #33599
-    is_test = os_env_exists("NVIM_TEST", false);
-  }
   bool is_set = false;
   switch (state) {
   case kTermModeNotRecognized:
   case kTermModePermanentlyReset:
     // TODO(bfredl): This is really ILOG but we want it in all builds.
     // add to show_verbose_terminfo() without being too racy ????
-    if (is_test == kFalse) {
+    if (!nvim_testing) {
+      // Very noisy in CI, don't log during tests. #33599
       WLOG("TUI: terminal mode %d unavailable, state %d", mode, state);
     }
     // If the mode is not recognized, or if the terminal emulator does not allow it to be changed,
@@ -238,7 +234,8 @@ void tui_handle_term_mode(TUIData *tui, TermMode mode, TermModeState state)
     FALLTHROUGH;
   case kTermModeReset:
     // The terminal supports changing the given mode
-    if (is_test == kFalse) {
+    if (!nvim_testing) {
+      // Very noisy in CI, don't log during tests. #33599
       WLOG("TUI: terminal mode %d detected, state %d", mode, state);
     }
     switch (mode) {

test/functional/core/startup_spec.lua

@@ -53,8 +53,7 @@ describe('startup', function()
 
   it('prevents remote UI infinite loop', function()
     clear()
-    local screen
-    screen = Screen.new(84, 3)
+    local screen = Screen.new(84, 3)
     fn.jobstart(
       { nvim_prog, '-u', 'NONE', '--server', eval('v:servername'), '--remote-ui' },
       { term = true }
@@ -84,8 +83,7 @@ describe('startup', function()
 
   it('-D does not hang #12647', function()
     clear()
-    local screen
-    screen = Screen.new(60, 7)
+    local screen = Screen.new(60, 7)
     -- not the same colors on windows for some reason
     screen._default_attr_ids = nil
     local id = fn.jobstart({
@@ -1414,16 +1412,18 @@ describe('user config init', function()
       write_file(
         table.concat({ xconfig, 'nvim', 'init.vim' }, pathsep),
         [[
-      let g:vim_rc = 1
-      ]]
+          let g:vim_rc = 1
+        ]]
       )
     end)
 
     it('loads default lua config, but shows an error', function()
       clear { args_rm = { '-u' }, env = xenv }
-      feed('<cr><c-c>') -- Dismiss "Conflicting config …" message.
       eq(1, eval('g:lua_rc'))
-      matches('^E5422: Conflicting configs', exec_capture('messages'))
+      t.matches(
+        'E5422: Conflicting configs: "Xhome.Xconfig.nvim.init.lua" "Xhome.Xconfig.nvim.init.vim"',
+        eval('v:errmsg')
+      )
     end)
   end)
 end)