patch 8.2.3766: converting a funcref to a string leaves out "g:"

Problem:    Converting a funcref to a string leaves out "g:", causing the
            meaning of the name depending on the context.
Solution:   Prepend "g:" for a global function.

src/eval.c

@@ -5006,6 +5006,14 @@ echo_string_core(
 		ga_concat(&ga, (char_u *)"function(");
 		if (fname != NULL)
 		{
+		    // When using uf_name prepend "g:" for a global function.
+		    if (pt->pt_name == NULL && fname[0] == '\''
+						      && vim_isupper(fname[1]))
+		    {
+			ga_concat(&ga, (char_u *)"'g:");
+			ga_concat(&ga, fname + 1);
+		    }
+		    else
 			ga_concat(&ga, fname);
 		    vim_free(fname);
 		}

src/testdir/test_functions.vim

@@ -2771,5 +2771,10 @@ func Test_builtin_check()
   call assert_fails('call extend(g:, #{bar: { -> "foo" }}, "force")', 'E704:')
 endfunc
 
+func Test_funcref_to_string()
+  let Fn = funcref('g:Test_funcref_to_string')
+  call assert_equal("function('g:Test_funcref_to_string')", string(Fn))
+endfunc
+
 
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -753,6 +753,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3766,
 /**/
     3765,
 /**/