[Issue 15970] New: C++ mangling of templated arg type

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15970

          Issue ID: 15970
           Summary: C++ mangling of templated arg type
           Product: D
           Version: D2
          Hardware: x86
                OS: Mac OS X
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: jbc.engelen at gmail.com

C++ mangling is wrong when a function takes an argument of type T (templated)
and when the typeof(T) is a class.

Test case:
```
extern(C++) class Symbol {}
extern(C++) class Symbol2 {}

extern(C++) class A(T) {
    void foo_template(T t) {}
    void foo_incorrect(Symbol t) {}
    void foo_correct(Symbol2 t) {}
}

A!int b_works;
A!Symbol b_incorrect;
```

Then running
> dmd -c cpp.d -ofcpp.o
> nm cpp.o | c++filt
gives the correct mangling for A!int:

A<int>::foo_correct(Symbol2*)
A<int>::foo_template(int)
A<int>::foo_incorrect(Symbol*)

but incorrect mangling for A!Symbol:

A<Symbol*>::foo_correct(Symbol2*)
A<Symbol*>::foo_template(A<Symbol*>)  <--- argument type wrong
A<Symbol*>::foo_incorrect(A<Symbol*>) <--- argument type wrong

--