dejagnu test fails to compile with clang `g++.old-deja/g++.pt/friend10.C`

[llvmbot]

Bugzilla Link	19095
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor,@spavloff

Extended Description

template <class T>
void f(T);

template <class U>
class C
{ 
  template <class T>
  friend void f(T)
  {
     C<U> c;
     c.i = 3;
  }
  
  public :
    
     void g()
     {
       f(3.0);
     }
    int i;
};

int main ()
{
  f(7);
  C<double> c;
  c.g();
}

This Test Case compiles with g++. Fails with clang, linker error - unable to find definition of function f() with following error :

Opensource/llvm/build/bin/clang friend10.C

/tmp/friend10-f7127e.o: In function `main':
friend10.C:(.text+0x16): undefined reference to `void f<int>(int)'
/tmp/friend10-f7127e.o: In function `C<double>::g()':
friend10.C:(.text._ZN1CIdE1gEv[_ZN1CIdE1gEv]+0x1b): undefined reference to `void f<double>(double)'
clang-3.5: error: linker command failed with exit code 1 (use -v to see invocation)

[spavloff]

Patch https://reviews.llvm.org/D21767 fixes this problem.

[AaronBallman]

Clang 7 demonstrates the issue. Starting in Clang 8, we incorrectly diagnosed the code. Then the issue was fixed in Clang 20: https://godbolt.org/z/czajrGo1s

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (llvmbot)

Details

| | | | --- | --- | | Bugzilla Link | [19095](https://llvm.org/bz19095) | | Version | trunk | | OS | Linux | | Reporter | LLVM Bugzilla Contributor | | CC | @DougGregor,@spavloff |

Extended Description

template <class T>
void f(T);

template <class U>
class C
{ 
  template <class T>
  friend void f(T)
  {
     C<U> c;
     c.i = 3;
  }
  
  public :
    
     void g()
     {
       f(3.0);
     }
    int i;
};

int main ()
{
  f(7);
  C<double> c;
  c.g();
}

This Test Case compiles with g++. Fails with clang, linker error - unable to find definition of function f() with following error :

Opensource/llvm/build/bin/clang friend10.C

/tmp/friend10-f7127e.o: In function `main':
friend10.C:(.text+0x16): undefined reference to `void f<int>(int)'
/tmp/friend10-f7127e.o: In function `C<double>::g()':
friend10.C:(.text._ZN1CIdE1gEv[_ZN1CIdE1gEv]+0x1b): undefined reference to `void f<double>(double)'
clang-3.5: error: linker command failed with exit code 1 (use -v to see invocation)