patch 8.2.3351: Vim9: using a function by name may delete it

Problem:    Vim9: using a function by name may delete it. (Naohiro Ono)
Solution:   Increment the reference count when using a function by name.
            (closes #8760)

Author: brammool

src/evalvars.c

@@ -2636,13 +2636,17 @@ eval_variable(
 	{
 	    ufunc_T *ufunc = find_func(name, FALSE, NULL);
 
+	    // In Vim9 script we can get a function reference by using the
+	    // function name.
 	    if (ufunc != NULL)
 	    {
 		found = TRUE;
 		if (rettv != NULL)
 		{
 		    rettv->v_type = VAR_FUNC;
 		    rettv->vval.v_string = vim_strsave(ufunc->uf_name);
+		    if (rettv->vval.v_string != NULL)
+			func_ref(ufunc->uf_name);
 		}
 	    }
 	}

src/testdir/test_vim9_func.vim

@@ -3089,6 +3089,23 @@ def Test_closing_brace_at_start_of_line()
   call CheckDefAndScriptSuccess(lines)
 enddef
 
+func CreateMydict()
+  let g:mydict = {}
+  func g:mydict.afunc()
+    let g:result = self.key
+  endfunc
+endfunc
+
+def Test_numbered_function_reference()
+  CreateMydict()
+  var output = execute('legacy func g:mydict.afunc')
+  var funcName = 'g:' .. substitute(output, '.*function \(\d\+\).*', '\1', '')
+  execute 'function(' .. funcName .. ', [], {key: 42})()'
+  # check that the function still exists
+  assert_equal(output, execute('legacy func g:mydict.afunc'))
+  unlet g:mydict
+enddef
+
 if has('python3')
   def Test_python3_heredoc()
     py3 << trim EOF

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3351,
 /**/
     3350,
 /**/