[llvm-bugs] [Bug 50864] New: An example code from the standard (templates and concepts) does not compile

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=50864

            Bug ID: 50864
           Summary: An example code from the standard (templates and
                    concepts) does not compile
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++2a
          Assignee: unassignedclangbugs at nondot.org
          Reporter: mikhail.matrosov at gmail.com
                CC: blitzrakete at gmail.com, erik.pilkington at gmail.com,
                    llvm-bugs at lists.llvm.org, richard-llvm at metafoo.co.uk

According to [temp.constr.decl]/4 the following example should compile:

template <class T> concept C = true;
template <class T> struct A {
  template <class U> U f(U) requires C<typename T::type>;   // #1
  template <class U> U f(U) requires C<T>;                  // #2
};

template <> template <class U>
U A<int>::f(U u) requires C<int> { return u; }              // OK, specializes
#2

However, clang gives an error:

<source>:3:49: error: type 'int' cannot be used prior to '::' because it has no
members
  template <class U> U f(U) requires C<typename T::type>;   // #1
                                                ^

I believe this is the reason why clang cannot compile libstdc++ ranges:
https://bugs.llvm.org/show_bug.cgi?id=46746

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