https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92060
Bug ID: 92060
Summary: Alias template as template template argument confused
by GCC as other template
Product: gcc
Version: 9.2.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: hstong at ca dot ibm.com
Target Milestone: ---
In the following, the alias template `Q` merely acts as a deducible template
([dcl.type.simple]) that behaves similarly to the class template `A`, it is not
the same template as `A`. GCC treats `Q` as `A` for the purposes of declaration
matching when used as a template template argument.
### SOURCE (<stdin>):
template <template <typename> class TT> struct AA;
template <typename> struct A;
template <typename T> using Q = A<T>;
void f(AA<A> *) { }
void f(AA<Q> *) { } // GCC claims this is a redefinition of f(AA<A> *).
### COMPILER INVOCATION:
g++ -fsyntax-only -std=c++2a -pedantic -Wall -Wextra -xc++ -
### EXPECTED OUTPUT:
(Clean compile).
### ACTUAL OUTPUT:
<stdin>:7:6: error: redefinition of 'void f(AA<A>*)'
<stdin>:6:6: note: 'void f(AA<A>*)' previously defined here
### COMPILER VERSION INFO (g++ -v):
Using built-in specs.
COLLECT_GCC=/opt/wandbox/gcc-9.2.0/bin/g++
COLLECT_LTO_WRAPPER=/opt/wandbox/gcc-9.2.0/libexec/gcc/x86_64-pc-linux-gnu/9.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-9.2.0/configure --prefix=/opt/wandbox/gcc-9.2.0
--enable-languages=c,c++ --disable-multilib --without-ppl --without-cloog-ppl
--enable-checking=release --disable-nls
LDFLAGS=-Wl,-rpath,/opt/wandbox/gcc-9.2.0/lib,-rpath,/opt/wandbox/gcc-9.2.0/lib64,-rpath,/opt/wandbox/gcc-9.2.0/lib32
--enable-lto
Thread model: posix
gcc version 9.2.0 (GCC)
