[Bug c/108700] New: false _Noreturn error with -Werror=old-style-declaration

[Bug c/108700] New: false _Noreturn error with -Werror=old-style-declaration

[vincent-gcc at vinc17 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108700

            Bug ID: 108700
           Summary: false _Noreturn error with
                    -Werror=old-style-declaration
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vincent-gcc at vinc17 dot net
  Target Milestone: ---

With gcc-12 (Debian 12.2.0-14) 12.2.0 (but this error was already present in
GCC 4.8):

cventin% echo 'int _Noreturn does_not_return (void) { for (;;) continue; }' |
gcc-12 -xc -c -Werror=old-style-declaration -
<stdin>:1:1: error: ‘_Noreturn’ is not at beginning of declaration
[-Werror=old-style-declaration]
cc1: some warnings being treated as errors

This error is incorrect. The grammar in ISO C17 is

function-definition:
  declaration-specifiers declarator declaration-listopt compound-statement

declaration-specifiers:
  storage-class-specifier declaration-specifiersopt
  type-specifier declaration-specifiersopt
  type-qualifier declaration-specifiersopt
  function-specifier declaration-specifiersopt
  alignment-specifier declaration-specifiersopt

where "int" is part of type-specifier and "_Noreturn" is part of
function-specifier, so that they can be in any order.

Note that the

  int _Noreturn does_not_return (void) { for (;;) continue; }

comes from one of the autoconf tests, which fails as a consequence.

[Bug c/108700] false _Noreturn error with -Werror=old-style-declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108700

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This has been warning since _Noreturn support was added back in r177881 .

[Bug c/108700] false _Noreturn error with -Werror=old-style-declaration

[vincent-gcc at vinc17 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108700

--- Comment #2 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
And there's the same issue with "inline" instead of "_Noreturn" (these are the
only two function specifiers).

[Bug c/108700] false _Noreturn error with -Werror=old-style-declaration

[schwab@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108700

--- Comment #3 from Andreas Schwab <schwab@linux-m68k.org> ---
The grammar doesn't tell everything, though currently only storage-class
specifiers are expected to occur at the beginning.

From c-parser.cc:c_parser_declspecs:
          /* TODO: Distinguish between function specifiers (inline, noreturn)
             and storage class specifiers, either here or in
             declspecs_add_scspec.  */