patch 9.1.0878: termdebug: cannot enable DEBUG mode

Problem:  termdebug: cannot enable DEBUG mode
Solution: Allow to specify DEBUG mode (Ubaldo Tiberi)

closes: #16080

Signed-off-by: Ubaldo Tiberi <ubaldo.tiberi@volvo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/testdir/test_termdebug.vim

@@ -57,6 +57,8 @@ endfunction
 
 packadd termdebug
 
+" should be the first test to run, since it validates the window layout with
+" win ids
 func Test_termdebug_basic()
   let bin_name = 'XTD_basic'
   let src_name = bin_name .. '.c'
@@ -620,4 +622,22 @@ function Test_termdebug_config_types()
   unlet g:termdebug_config
 endfunction
 
+function Test_termdebug_config_debug()
+  let s:error_message = '\[termdebug\] Termdebug already loaded'
+
+  " USER mode: No error message shall be displayed
+  packadd termdebug
+  call assert_true(execute('messages') !~ s:error_message)
+
+  " DEBUG mode: Error message shall now be displayed
+  let g:termdebug_config = {}
+  let g:termdebug_config['debug'] = 1
+  packadd termdebug
+  call assert_true(execute('messages') =~ s:error_message)
+
+  unlet g:termdebug_config
+  unlet g:termdebug_loaded
+  " Revert DEBUG mode, by reloading the plugin
+  source $VIMRUNTIME/pack/dist/opt/termdebug/plugin/termdebug.vim
+endfunction
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    878,
 /**/
     877,
 /**/