Fix Issue 21753 - Struct literal with function literal member not allowed as template value argument

Author: BorisCarvajal

src/dmd/dmangle.d

@@ -1267,6 +1267,14 @@ public:
         }
     }
 
+    override void visit(FuncExp e)
+    {
+        if (e.td)
+            mangleSymbol(e.td);
+        else
+            mangleSymbol(e.fd);
+    }
+
     ////////////////////////////////////////////////////////////////////////////
 
     override void visit(Parameter p)

test/runnable/mangle.d

@@ -618,6 +618,12 @@ static assert(funcd.mangleof == "_D6mangle5funcdFPFZNnZi");
 
 /***************************************************/
 
+struct S21753 { void function() f1; }
+void fun21753(S21753 v)() {}
+alias fl21753 = (){};
+static assert((fun21753!(S21753(fl21753))).mangleof == "_D6mangle__T8fun21753VSQv6S21753S1_DQBi10" ~ fl21753.stringof ~ "MFNaNbNiNfZvZQCaQp");
+
+/***************************************************/
 void main()
 {
     test10077h();