http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55127
Bug #: 55127
Summary: [4.8 regression] Incorrect "dependent scope" error
with partial specialisation of non-type parameter
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: gccb...@qo.cx
The current GCC snapshot in Debian unstable seems to reject valid code (mininal
test case attached).
In a template function context, accessing a nested type of a template
instantiation of an unrelated(!) template class may be flagged as requiring a
'typename' for being a dependent scope.
AFAICS, it only happens in case of the instantiated template being partially
specialised for a non-type template parameter, like bool here:
struct some_class
{
static const bool is_valid_type = true;
};
template< typename Type
, bool Valid = Type::is_valid_type >
struct wrapper;
template< typename Type >
struct wrapper< Type, true > { ... };
template< typename T >
int fun()
{
wrapper< some_class >::type x; // fails w/ 4.8.0
}
$ g++-snapshot -c -o typename-bug.o typename-bug.cpp
typename-bug.cpp: In function 'void fun()':
typename-bug.cpp:29:3: error: need 'typename' before
'wrapper::type' because 'wrapper' is a dependent scope
wrapper::type x;
^
typename-bug.cpp:29:29: error: expected ';' before 'x'
wrapper::type x;
^
typename-bug.cpp: In instantiation of 'void fun() [with T = int]':
typename-bug.cpp:34:12: required from here
typename-bug.cpp:29:3: error: dependent-name 'wrapper::type' is
parsed as a non-type, but instantiation yields a type
wrapper::type x;
^
typename-bug.cpp:29:3: note: say 'typename wrapper::type' if a type
is meant
A possible workaround is to partially specialise via a type parameter (as shown
in the attached file with WORKAROUND being defined).
The failing GCC version reports:
Using built-in specs.
COLLECT_GCC=g++-snapshot
COLLECT_LTO_WRAPPER=/usr/lib/gcc-snapshot/libexec/gcc/i486-linux-gnu/4.8.0/lto-wrapper
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 20121008-1'
--with-bugurl=file:///usr/share/doc/gcc-snapshot/README.Bugs
--enable-languages=c,ada,c++,java,go,fortran,objc,obj-c++
--prefix=/usr/lib/gcc-snapshot --enable-shared --enable-linker-build-id
--with-system-zlib --disable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--enable-plugin --disable-browser-plugin --enable-java-awt=gtk
--enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-snap/jre
--enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-snap
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-snap
--with-arch-directory=i386 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-targets=all --with-arch-32=i586 --with-tune=generic
--disable-werror --enable-checking=yes --build=i486-linux-gnu
--host=i486-linux-gnu --target=i486-linux-gnu
Thread model: posix
gcc version 4.8.0 20121008 (experimental) [trunk revision 192192] (Debian
20121008-1)
Code is accepted by all "other" GCC variants in Debian testing/unstable:
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.7-3'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran --prefix=/usr --program-suffix=-4.4
--enable-shared --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-targets=all
--with-arch-32=i586 --with-tune=generic --enable-checking=release
--build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu
Thread model: posix
gcc version 4.4.7 (Debian 4.4.7-3)
Using built-in specs.
COLLECT_GCC=g++-4.6
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i486-linux-gnu/4.6/lto-wrapper
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.6.3-12'
--with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.6 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--enable-plugin --enable-objc-gc --enable-targets=all --with-arch-32=i586
--with-tune=generic --enable-checking=release --build=i486-linux-gnu
