input: skip dialogs if no UI is active

Treat dialogs in the same way as "silent mode" (`nvim -es`).

References #1984
References #3901

runtime/doc/starting.txt

@@ -53,7 +53,7 @@ filename	One or more file names.  The first one will be the current
 <		Starting in Ex mode: >
 			nvim -e -
 			nvim -E
-<		Start editing in silent mode.  See |-s-ex|.
+<		Start editing in |silent-mode|.
 
 							*-t* *-tag*
 -t {tag}	A tag.  "tag" is looked up in the tags file, the associated
@@ -200,7 +200,7 @@ argument.
 							*-E*
 -E		Start Vim in improved Ex mode |gQ|.
 
-							*-s-ex*
+							*-s-ex* *silent-mode*
 -s		Silent or batch mode.  Only when "-s" is preceded by the "-e"
 		argument.  Otherwise see |-s|, which does take an argument
 		while this use of "-s" doesn't.  To be used when Vim is used
@@ -221,7 +221,7 @@ argument.
 		Initializations are skipped (except the ones given with the
 		"-u" argument).
 		Example: >
-			vim -e -s  < thefilter  thefile
+			vim -es < thefilter  thefile
 <
 							*-b*
 -b		Binary mode.  File I/O will only recognize <NL> to separate
@@ -351,6 +351,7 @@ argument.
 
 							*--headless*
 --headless 	Do not start the built-in UI.
+		See also |silent-mode|, which does start a (limited) UI.
 
 ==============================================================================
 2. Initialization				*initialization* *startup*

src/nvim/main.c

@@ -98,10 +98,8 @@ typedef struct {
   bool input_isatty;                    // stdin is a terminal
   bool output_isatty;                   // stdout is a terminal
   bool err_isatty;                      // stderr is a terminal
-  bool headless;                        // Dont try to start an user interface
-                                        // or read/write to stdio(unless
-                                        // embedding)
-  int no_swap_file;                     /* "-n" argument used */
+  bool headless;                        // Do not start the builtin UI.
+  int no_swap_file;                     // "-n" argument used
   int use_debug_break_level;
   int window_count;                     /* number of windows to use */
   int window_layout;                    /* 0, WIN_HOR, WIN_VER or WIN_TABS */
@@ -932,10 +930,11 @@ static void command_line_scan(mparm_T *parmp)
           break;
 
         case 's':
-          if (exmode_active)              /* "-s" silent (batch) mode */
-            silent_mode = TRUE;
-          else                    /* "-s {scriptin}" read from script file */
-            want_argument = TRUE;
+          if (exmode_active) {    // "-es" silent (batch) mode
+            silent_mode = true;
+          } else {                // "-s {scriptin}" read from script file
+            want_argument = true;
+          }
           break;
 
         case 't':                 /* "-t {tag}" or "-t{tag}" jump to tag */

src/nvim/message.c

@@ -2722,9 +2722,11 @@ do_dialog (
   int c;
   int i;
 
-  /* Don't output anything in silent mode ("ex -s") */
-  if (silent_mode)
-    return dfltbutton;       /* return default option */
+  if (silent_mode      // No dialogs in silent mode ("ex -s")
+      || !ui_active()  // Without a UI Nvim waits for input forever.
+      ) {
+    return dfltbutton;  // return default option
+  }
 
 
   oldState = State;

src/nvim/misc1.c

@@ -2203,7 +2203,7 @@ change_warning (
     set_vim_var_string(VV_WARNINGMSG, _(w_readonly), -1);
     msg_clr_eos();
     (void)msg_end();
-    if (msg_silent == 0 && !silent_mode) {
+    if (msg_silent == 0 && !silent_mode && ui_active()) {
       ui_flush();
       os_delay(1000L, true);       /* give the user time to think about it */
     }

src/nvim/testdir/test49.vim

@@ -481,12 +481,9 @@ function! ExtraVim(...)
     bwipeout
     let g:Xpath = g:Xpath + sum
 
-    " FIXME(nvim): delete() of a file used by a subprocess hangs TSAN build on travis CI.
-    if !empty($TRAVIS)
     " Delete the extra script and the resultfile.
     call delete(extra_script)
     call delete(resultfile)
-    endif
 
     " Switch back to the buffer that was active when this function was entered.
     exec "buffer" current_buffnr

test/functional/ui/wildmode_spec.lua

@@ -1,7 +1,7 @@
 local helpers = require('test.functional.helpers')(after_each)
 local Screen = require('test.functional.ui.screen')
 local clear, feed, command = helpers.clear, helpers.feed, helpers.command
-local iswin, set_shell_powershell = helpers.iswin, helpers.set_shell_powershell
+local iswin = helpers.iswin
 local funcs = helpers.funcs
 local eq = helpers.eq
 local eval = helpers.eval
@@ -124,12 +124,9 @@ describe("'wildmenu'", function()
     -- must wait the full timeout. So make it reasonable.
     screen.timeout = 1000
 
-    if iswin() then
-      set_shell_powershell()
-    else
-      command('set shell=sh')
+    if not iswin() then
+      command('set shell=sh')  -- Need a predictable "$" prompt.
     end
-
     command('set laststatus=0')
     command('vsplit')
     command('term')
@@ -137,7 +134,7 @@ describe("'wildmenu'", function()
     -- Check for a shell prompt to verify that the terminal loaded.
     retry(nil, nil, function()
       if iswin() then
-        eq('PS', eval("matchstr(join(getline(1, '$')), 'PS')"))
+        eq('Microsoft', eval("matchstr(join(getline(1, '$')), 'Microsoft')"))
       else
         eq('$', eval([[matchstr(getline(1), '\$')]]))
       end