[llvm-bugs] [Bug 43265] New: Unclear error message shadowing/init with itself; should possibly be another compiler error

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https://bugs.llvm.org/show_bug.cgi?id=43265

            Bug ID: 43265
           Summary: Unclear error message shadowing/init with itself;
                    should possibly be another compiler error
           Product: clang
           Version: 9.0
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: jvapen at gmail.com
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

// clang-cl.exe /nologo /c -Weverything /GR /EHsc  t.cpp 
enum class E {
  A = 1
};

template <E e> struct C { static constexpr E e = e; /*shadowing!*/ };

template <class C> void g() { static_assert(C::e == E::A); }

void f() { g< C<E::A> >(); }


>> Error: (both 7.0.0 as 9.0.0-RC3)
t.cpp(7,31): error: static_assert failed due to requirement 'C<E::A>::e ==
E::A'
template <class C> void g() { static_assert(C::e == E::A); }
                              ^             ~~~~~~~~~~~~

Looking at the code above, I've found out that the initialization of
static constexpr E e = e;
is actually initializing with zero initialization followed by initializing with
itself?

The error was not that obvious without the reduction.
I see multiple issues:
 - the template 'e' is shadowing the constexpr 'e' -> We don't get a warning on
this
 - constexpr 'e' is being initialized with a value not in the enumeration ->
not sure if this is an error (is it UB?), however, it at least deserves a
warning (I'm pretty sure I already saw it at another place)
 - Bonus points: Can we, similar to the template arguments, get some 'aka' for
nummerics/types used: example: static_assert(0 == 1);

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