[PATCH] Sema: Treat zero sized arrays as flexible array members

[Arthur O'Dwyer]

On Wed, Sep 24, 2014 at 4:22 AM, David Majnemer
<david.majnemer at gmail.com> wrote:
> Hi rsmith, rnk, andreadb,
>
> Zero sized arrays are more or less the pre-standard version of flexible
> array members.  It makes sense to mark structs which contain them as
> hasFlexibleArrayMember.
>
> Doing this has the side effect of resolving PR21040, a crash involving
> one record inheriting from a base which is terminated with a zero sized
> array field.
>
> http://reviews.llvm.org/D5478

Drive-by comments:

(1) What effect does this have on templates, e.g.
    template<int N> struct A { int a[N]; };
    struct B : private A<0> { int b; };
    struct C { A<0> a; int c; };
? IIUC, Clang used to produce a GCC-style "array with size zero" in
this case, and now produces a hard error.  Your new code is justified,
IMHO, but could you add a test case involving templates or other
sneaky code, just to be explicit that the new behavior is 100%
intended?

(2) Unfortunately unrelated to your patch: The error is "base class
'A' has a flexible array member", but it doesn't generate a note
pointing to the flexible array member's declaration, nor even mention
the name of the flexible array member. IMHO it should, especially now
that a "flexible array member" may have an innocent-looking
declaration of the form "int a[N]".

my $.02,
–Arthur