[Bug c++/66690] New: error: use of âXâ before deduction of âautoâ

["cas43 at cs dot stanford.edu" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66690

            Bug ID: 66690
           Summary: error: use of âXâ before deduction of âautoâ
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cas43 at cs dot stanford.edu
  Target Milestone: ---

PROBLEM:

When compiling the (invalid) code below, two diagnostics are issued.  The first
is valid (constructor is private).  The second diagnostic is perplexing. 
Fixing the error results in a clean compile.

CODE:

template<class T> auto foo(T t) {return 3;}
class B {B();};
template<class T> class D:public B
{
    D()
    {
        T x00;
        foo(x00);
    }
};
D<int> d;

DIAGNOSTIC:

prog.cpp:5:5: error: âD<T>::D() [with T = int]â is private
     D()
     ^
prog.cpp:11:8: error: within this context
 D<int> d;
        ^
prog.cpp: In instantiation of âD<T>::D() [with T = int]â:
prog.cpp:11:8:   required from here
prog.cpp:2:10: error: âB::B()â is private
 class B {B();};
          ^
prog.cpp:6:5: error: within this context
     {
     ^
prog.cpp:8:12: error: use of âauto foo(T) [with T = int]â before deduction of
âautoâ
         foo(x00);
            ^


VERSION:

Using built-in specs.
COLLECT_GCC=g++-5
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
5.1.0-0ubuntu11~14.04.1' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs
--enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-5 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=c++98 --enable-gnu-unique-object
--disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib
--disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home
--with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 5.1.0 (Ubuntu 5.1.0-0ubuntu11~14.04.1)