[Bug c/101265] New: C2X [[maybe_unused]] ignored when placed after array declaration

[gcc at alanwu dot email]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101265

            Bug ID: 101265
           Summary: C2X [[maybe_unused]] ignored when placed after array
                    declaration
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc at alanwu dot email
  Target Milestone: ---

With the following:

    void foo(void) {
        [[maybe_unused]] int thisworks[1];
        int thisdoesnt[1] [[maybe_unused]];
    }

GCC 11 warns:

    $ gcc-11 -std=c2x -pedantic -Wall -c test.c
    test.c: In function 'foo':
    test.c:3:5: warning: 'maybe_unused' attribute ignored [-Wattributes]
        3 |     int thisdoesnt[1] [[maybe_unused]];
          |     ^~~
    test.c:3:9: warning: unused variable 'thisdoesnt' [-Wunused-variable]
        3 |     int thisdoesnt[1] [[maybe_unused]];
          |         ^~~~~~~~~~

Is this a bug? I'm not familiar with the spec. By the way, `g++-11`
doesn't emit any warnings for the same file and `clang` seems to also accept
it.

gcc-11 -v:

    COLLECT_GCC=gcc-11
    COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/11/lto-wrapper
    OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
    OFFLOAD_TARGET_DEFAULT=1
    Target: x86_64-linux-gnu
    Configured with: ../src/configure -v --with-pkgversion='Ubuntu
11.1.0-1ubuntu1~20.04' --with-bugurl=file:///usr/share/doc/gcc-11/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-11
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --disable-cet
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-11-2V7zgg/gcc-11-11.1.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-11-2V7zgg/gcc-11-11.1.0/debian/tmp-gcn/usr
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-serialization=2
    Thread model: posix
    Supported LTO compression algorithms: zlib zstd
    gcc version 11.1.0 (Ubuntu 11.1.0-1ubuntu1~20.04)

It seems to reproduce on trunk on Compiler Explorer:

    gcc
(Compiler-Explorer-Build-gcc-7c6b354b92b38f31cd2399fbdbc9d6f837881480-binutils-2.36.1)
12.0.0 20210628 (experimental)