[Bug c++/84009] New: No diagnostic issued if the decl-specifier in the decl-specifier-seq of a for-range-declaration is register, static,or thread_local

[smw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84009

            Bug ID: 84009
           Summary: No diagnostic issued if the decl-specifier in the
                    decl-specifier-seq of a for-range-declaration is
                    register, static,or thread_local
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: smw at gcc dot gnu.org
  Target Milestone: ---

The C++ standard requires the decl-specifier in the decl-specifier-seq of a
for-range-declaration shall be either a type-specifier or constexpr
([stmt.ranged]/2).  GCC does so for most decl-specifiers (eg. "friend",
"mutable", "extern", etc) but not for "register," "static," or "thread_local." 
This is in C++14 mode (so, um, "register" isn't even a valid decl-specifier any
more).

clang, MSVC, ICC all give appropriate diagnostics in this case. GCC (all
versions tested, up to 8.0.1 20180117) remains mute.

Here's a sample bit of code that should not compile silently.

    void f() {
        int a[] = { 1, 2, 3 };
        for (register int& i : a) {
           // ...
        }
    }