[llvm-bugs] [Bug 38301] New: compilation of CRTP fails if the ABC is after template

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38301

            Bug ID: 38301
           Summary: compilation of CRTP fails if the ABC is after template
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: zhonghao at pku.org.cn
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org

the compilation of a curious recuring template fails if the base class for the
instantiation of the curious recuring template pattern (CRTP) is defined after
the template but before its instantiation.

The following code demonstrates the problem. If uncommenting the outcommented
section and commenting out the latter appearance of the same code, it compiles
successfully.

#include <iostream>

using namespace std;

/*
struct Client
{
        void visit(const class A &a)
        { cout << "Client::visit(const A &)" << endl; }
};

struct MYABC
{
        virtual void runVisitor(class Client &) const = 0;
};
*/

template <class Derived, class ABC>
struct Door : public ABC
{
        Door()
        : ABC()
        { }

        void runVisitor(class Client &) const;
};

template <class Derived, class ABC>
void Door<Derived,ABC>::runVisitor(class Client &c) const
{ c.visit(static_cast<const Derived &>(*this)); }

struct Client
{
        void visit(const class A &a)
        { cout << "Client::visit(const A &)" << endl; }
};

struct MYABC
{
        virtual void runVisitor(class Client &) const = 0;
};

struct A : public Door<A,MYABC>
{
};

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