[llvm-bugs] [Bug 26448] New: Ternary operator: Incorrect value category

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=26448

            Bug ID: 26448
           Summary: Ternary operator: Incorrect value category
           Product: clang
           Version: 3.7
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: roman.perepelitsa at gmail.com
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org
    Classification: Unclassified

The following program unexpectedly triggers the static assertion.

  #include <type_traits>

  template <class T, class U>
  using common = decltype(true ? std::declval<T>() : std::declval<U>());

  struct base {};
  struct derived : base {};

  // common<base, derived> is expected to be base&& (see [expr.cond]/3.2),
  // but clang produces base. Hence the assertion fails.
  static_assert(std::is_same<common<base, derived>, base&&>(), "");

GCC works correctly on this code snippet.

Note that the following assertion holds (expected behaviour):

  static_assert(std::is_same<common<base, base>, base&&>(), "");

Confirmed for clang up to 3.7.1 via gcc.godbolt.org (http://goo.gl/srkhK5).

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