patch 8.2.3828: when opening a terminal from a timer first typed char is lost

Problem:    when opening a terminal from a timer the first typed character
            is lost. (Virginia Senioria)
Solution:   When opening a terminal while waiting for a character put K_IGNORE
            in the input buffer.

src/edit.c

@@ -598,9 +598,14 @@ edit(
 	    {
 		c = safe_vgetc();
 
-		if (stop_insert_mode)
+		if (stop_insert_mode
+#ifdef FEAT_TERMINAL
+			|| (c == K_IGNORE && term_use_loop())
+#endif
+		   )
 		{
-		    // Insert mode ended, possibly from a callback.
+		    // Insert mode ended, possibly from a callback, or a timer
+		    // must have opened a terminal window.
 		    if (c != K_IGNORE && c != K_NOP)
 			vungetc(c);
 		    count = 0;

src/terminal.c

@@ -739,6 +739,23 @@ term_start(
 	    curwin->w_buffer = curbuf;
 	    ++curbuf->b_nwindows;
 	}
+	else if (vgetc_busy
+#ifdef FEAT_TIMERS
+		|| timer_busy
+#endif
+		|| input_busy)
+	{
+	    char_u ignore[4];
+
+	    // When waiting for input need to return and possibly end up in
+	    // terminal_loop() instead.
+	    ignore[0] = K_SPECIAL;
+	    ignore[1] = KS_EXTRA;
+	    ignore[2] = KE_IGNORE;
+	    ignore[3] = NUL;
+	    ins_typebuf(ignore, REMAP_NONE, 0, TRUE, FALSE);
+	    typebuf_was_filled = TRUE;
+	}
     }
     else
     {

src/testdir/test_terminal.vim

@@ -1596,6 +1596,7 @@ endfunc
 " 4. 0.5 sec later: should be done, clean up
 func Test_terminal_statusline()
   CheckUnix
+  CheckFeature timers
 
   set statusline=x
   terminal
@@ -1611,6 +1612,31 @@ func Test_terminal_statusline()
   set statusline=
 endfunc
 
+func CheckTerminalWindowWorks(buf)
+  call WaitForAssert({-> assert_match('!sh \[running\]', term_getline(a:buf, 10))})
+  call term_sendkeys(a:buf, "exit\<CR>")
+  call WaitForAssert({-> assert_match('!sh \[finished\]', term_getline(a:buf, 10))})
+  call term_sendkeys(a:buf, ":q\<CR>")
+  call WaitForAssert({-> assert_match('^\~', term_getline(a:buf, 10))})
+endfunc
+
+func Test_start_terminal_from_timer()
+  CheckUnix
+  CheckFeature timers
+
+  " Open a terminal window from a timer, typed text goes to the terminal
+  call writefile(["call timer_start(100, { -> term_start('sh') })"], 'XtimerTerm')
+  let buf = RunVimInTerminal('-S XtimerTerm', {})
+  call CheckTerminalWindowWorks(buf)
+
+  " do the same in Insert mode
+  call term_sendkeys(buf, ":call timer_start(200, { -> term_start('sh') })\<CR>a")
+  call CheckTerminalWindowWorks(buf)
+
+  call StopVimInTerminal(buf)
+  call delete('XtimerTerm')
+endfunc
+
 func Test_terminal_window_focus()
   let winid1 = win_getid()
   terminal

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3828,
 /**/
     3827,
 /**/