[llvm-bugs] [Bug 30365] New: Class template member function out-of-line definition dependent parameter uses declaration topmost cv-qualification

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https://llvm.org/bugs/show_bug.cgi?id=30365

            Bug ID: 30365
           Summary: Class template member function out-of-line definition
                    dependent parameter uses declaration topmost
                    cv-qualification
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: ed at catmur.co.uk
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org
    Classification: Unclassified

In a class template member function out-of-line definition, with a parameter
dependent on class template parameters and differing in topmost
cv-qualification between declaration and definition, clang uses the parameter
type of the declaration rather than the parameter type of the definition,
incorrectly accepting this program:

template<class T> struct A { void f(typename T::U); };
template<class T> void A<T>::f(typename T::U const i) { i = 1; }  // no error
struct X { using U = int; };
int main() { A<X>{}.f(0); }

Expected error:
cannot assign to variable 'i' with const-qualified type 'const typename X::U'
(aka 'const int')

If the cv-qualifiers are swapped (const present on the declaration, not on the
definition), clang incorrectly rejects the program:

template<class T> struct A { void f(typename T::U const); };
template<class T> void A<T>::f(typename T::U i) { i = 1; }  // error
struct X { using U = int; };
int main() { A<X>{}.f(0); }

gcc and MSVC compile both these correctly; ICC has the same bug as clang.

Tested versions 3.0-3.9.

References: [class.mfct]/1, [dcl.fct]/5.

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