patch 8.2.3082: a channel command "echoerr" does not show anything

Problem:    A channel command "echoerr" does not show anything.
Solution:   Do not use silent errors when using an "echoerr" command.
            (closes #8494)

src/channel.c

@@ -2486,12 +2486,17 @@ channel_exe_cmd(channel_T *channel, ch_part_T part, typval_T *argv)
 
     if (STRCMP(cmd, "ex") == 0)
     {
-	int called_emsg_before = called_emsg;
+	int	called_emsg_before = called_emsg;
+	char_u	*p = arg;
+	int	do_emsg_silent;
 
 	ch_log(channel, "Executing ex command '%s'", (char *)arg);
-	++emsg_silent;
+	do_emsg_silent = !checkforcmd(&p, "echoerr", 5);
+	if (do_emsg_silent)
+	    ++emsg_silent;
 	do_cmdline_cmd(arg);
-	--emsg_silent;
+	if (do_emsg_silent)
+	    --emsg_silent;
 	if (called_emsg > called_emsg_before)
 	    ch_log(channel, "Ex command error: '%s'",
 					  (char *)get_vim_var_str(VV_ERRMSG));

src/testdir/test_channel.py

@@ -109,6 +109,11 @@ class ThreadedTCPRequestHandler(socketserver.BaseRequestHandler):
                         print("sending: {0}".format(cmd))
                         self.request.sendall(cmd.encode('utf-8'))
                         response = "ok"
+                    elif decoded[1] == 'echoerr':
+                        cmd = '["ex","echoerr \\\"this is an error\\\""]'
+                        print("sending: {0}".format(cmd))
+                        self.request.sendall(cmd.encode('utf-8'))
+                        response = "ok"
                     elif decoded[1] == 'bad command':
                         cmd = '["ex","foo bar"]'
                         print("sending: {0}".format(cmd))

src/testdir/test_channel.vim

@@ -115,6 +115,18 @@ func Ch_communicate(port)
   call WaitForAssert({-> assert_equal("added2", getline("$"))})
   call assert_equal('added1', getline(line('$') - 1))
 
+  " Request command "echoerr 'this is an error'".
+  " This will throw an exception, catch it here.
+  let caught = 'no'
+  try
+    call assert_equal('ok', ch_evalexpr(handle, 'echoerr'))
+  catch /this is an error/
+    let caught = 'yes'
+  endtry
+  if caught != 'yes'
+    call assert_report("Expected exception from error message")
+  endif
+
   " Request command "foo bar", which fails silently.
   call assert_equal('ok', ch_evalexpr(handle, 'bad command'))
   call WaitForAssert({-> assert_match("E492:.*foo bar", v:errmsg)})

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3082,
 /**/
     3081,
 /**/