[Bug c++/96039] New: Missing diagnostic: C++11 alignment specifier on bit-fields

[hstong at ca dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96039

            Bug ID: 96039
           Summary: Missing diagnostic: C++11 alignment specifier on
                    bit-fields
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hstong at ca dot ibm.com
  Target Milestone: ---

According to [dcl.align] in the 2020 DIS for C++, an alignment-specifier shall
not be applied to a bit-field. GCC allows such alignment-specifiers with no
diagnostic.

### SOURCE (<stdin>):
struct A {
  int x alignas(long long) : 32;
};


### COMPILER INVOCATION:
g++ -fsyntax-only -std=c++11 -Wall -Wextra -pedantic-errors -xc++ -


### ACTUAL OUTPUT:
(rc=0)


### EXPECTED OUTPUT:
Diagnostic message; likely an error.


### COMPILER VERSION INFO (g++ -v):
Using built-in specs.
COLLECT_GCC=/opt/wandbox/gcc-head/bin/g++
COLLECT_LTO_WRAPPER=/opt/wandbox/gcc-head/libexec/gcc/x86_64-pc-linux-gnu/11.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../source/configure --prefix=/opt/wandbox/gcc-head
--enable-languages=c,c++ --disable-multilib --without-ppl --without-cloog-ppl
--enable-checking=release --disable-nls --enable-lto
LDFLAGS=-Wl,-rpath,/opt/wandbox/gcc-head/lib,-rpath,/opt/wandbox/gcc-head/lib64,-rpath,/opt/wandbox/gcc-head/lib32
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 11.0.0 20200701 (experimental) (GCC)