incorrect has internal linkage but is not defined `[-Wundefined-internal]` reported when a private class is used in a template

[llvmbot]

Bugzilla Link	20296
Version	3.4
OS	All
Attachments	source files used in the description
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor,@zahiraam

Extended Description

When trying to compile the following program:

cat tmp.cpp

template <template<typename A> class T>
class E {
public:
   typedef T<E> EType;
};


class Foo {
public:
   template<typename A>
   struct Nested { };

private:
   typedef Foo Type;
   typedef E<Nested>::EType EType;

public:
   typedef void (*MethodType)(EType& n);
public:
   static void adaptMethod(EType& n);

public:
   Foo()
      : _method(&Type::adaptMethod) { }

private:
   MethodType _method;
};

I get:

 clang++ -v -c -std=c++11 tmp.cpp
clang version 3.4 (http://llvm.org/git/clang 48eff6c3512fd6c768072b05ab4c287c7719072b) (http://llvm.org/git/llvm 8240ef04108620fef51219e9495a6e71e95ccd75)
Target: x86_64-unknown-linux-gnu
Thread model: posix
 "/dbc/sof2-dbc201/gdimitrov/sysroot/bin/clang" -cc1 -triple x86_64-unknown-linux-gnu -emit-obj -mrelax-all -disable-free -main-file-name tmp.cpp -mrelocation-model static -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -target-cpu x86-64 -target-linker-version 2.20.51.0.2 -v -coverage-file /dbc/sof2-dbc201/gdimitrov/git-src/cayman/vapicpp_cfg/vapicpp/src/tmp.o -resource-dir /dbc/sof2-dbc201/gdimitrov/sysroot/bin/../lib/clang/3.4 -internal-isystem /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7 -internal-isystem /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/x86_64-redhat-linux -internal-isystem /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/backward -internal-isystem /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/x86_64-redhat-linux/c++/4.4.7 -internal-isystem /usr/local/include -internal-isystem /dbc/sof2-dbc201/gdimitrov/sysroot/bin/../lib/clang/3.4/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /dbc/sof2-dbc201/gdimitrov/git-src/cayman/vapicpp_cfg/vapicpp/src -ferror-limit 19 -fmessage-length 318 -mstackrealign -fobjc-runtime=gcc -fobjc-default-synthesize-properties -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -backend-option -vectorize-loops -o tmp.o -x c++ tmp.cpp
clang -cc1 version 3.4 based upon LLVM 3.4svn default target x86_64-unknown-linux-gnu

tmp.cpp:20:16: warning: function 'Foo::adaptMethod' has internal linkage but is not defined [-Wundefined-internal]
   static void adaptMethod(EType& n);
               ^
tmp.cpp:24:24: note: used here
      : _method(&Type::adaptMethod) { }
                       ^
1 warning generated.

The same code compiles fine with clang 3.2 and gcc 4.4, 4.8

If I change the code to this:

% cat tmp2.cpp

template <template<typename A> class T>
class E {
public:
   typedef T<E> EType;
};


template<typename A>
struct Nested { };   // Moved the class outside of Foo

class Foo {
public:
private:
   typedef Foo Type;
   typedef E<Nested>::EType EType;

public:
   typedef void (*MethodType)(EType& n);
public:
   static void adaptMethod(EType& n);

public:
   Foo()
      : _method(&Type::adaptMethod) { }

private:
   MethodType _method;
};

Or I change it to this:

cat tmp3.cpp

template <template<typename A> class T>
class E {
public:
   typedef T<int> EType; // use "int" instead of "E"
};


class Foo {
public:
   template<typename A>
   struct Nested { };

private:
   typedef Foo Type;
   typedef E<Nested>::EType EType;

public:
   typedef void (*MethodType)(EType& n);
public:
   static void adaptMethod(EType& n);

public:
   Foo()
      : _method(&Type::adaptMethod) { }

private:
   MethodType _method;
};

There is no warning issued.

[llvmbot]

I use Ubuntu clang version 3.4-1ubuntu3 (tags/RELEASE_34/final) (based on LLVM 3.4)
Target: x86_64-pc-linux-gnu

The problem also shows for me when all members of Foo in the testcase are public.

Furthermore when actually providing a definition for Foo::adaptMethod:

  void Foo::adaptMethod(Foo::EType &n)
  {
  }

The warning goes away but the symbol really is internal and can not be linked to.
GCC emits _ZN3Foo11adaptMethodERNS_6NestedI1EINS_6NestedEEEE.

[AaronBallman]

This issue was fixed in Clang 3.5: https://godbolt.org/z/xMbd8bnbz