Re: C++ PATCH for c++/89024 - ICE with incomplete enum type

[Jason Merrill <jason@redhat.com>]

On Mon, Jan 28, 2019 at 10:40 AM Marek Polacek <polacek@redhat.com> wrote:
> On Mon, Jan 28, 2019 at 10:37:01AM +0100, Christophe Lyon wrote:
> > On Sun, 27 Jan 2019 at 01:25, Jason Merrill <jason@redhat.com> wrote:
> > >
> > > On Fri, Jan 25, 2019 at 6:22 PM Marek Polacek <polacek@redhat.com> wrote:
> > > >
> > > > On Fri, Jan 25, 2019 at 12:14:07PM -0500, Jason Merrill wrote:
> > > > > On 1/25/19 12:09 PM, Marek Polacek wrote:
> > > > > > On Fri, Jan 25, 2019 at 10:55:55AM -0600, Tim Song wrote:
> > > > > > > On Thu, Jan 24, 2019 at 4:14 PM Jason Merrill <jason@redhat.com> wrote:
> > > > > > > >
> > > > > > > > On 1/24/19 2:16 PM, Marek Polacek wrote:
> > > > > > > > > This test ICEs since r159006 which added
> > > > > > > > >
> > > > > > > > >      type = ENUM_UNDERLYING_TYPE (type);
> > > > > > > > >
> > > > > > > > > to type_promotes_to.  In this test ENUM_UNDERLYING_TYPE is null because we
> > > > > > > > > haven't yet parsed '}' of the enum and the underlying type isn't fixed, and
> > > > > > > > > so checking TYPE_UNSIGNED crashed.
> > > > > > > > >
> > > > > > > > > I've added some checks to the test to see if the types seem to be OK; clang++
> > > > > > > > > agrees.
> > > > > > > > >
> > > > > > > > > Bootstrapped/regtested on x86_64-linux, ok for trunk/8/7?
> > > > > > > > >
> > > > > > > > > 2019-01-24  Marek Polacek  <polacek@redhat.com>
> > > > > > > > >
> > > > > > > > >        PR c++/89024 - ICE with incomplete enum type.
> > > > > > > > >        * cvt.c (type_promotes_to): Check if prom is non-null.
> > > > > > > >
> > > > > > > > 9.6/6: An enumeration whose underlying type is not fixed is an
> > > > > > > > incomplete type from its point of declaration to immediately after the
> > > > > > > > closing } of its enum-specifier, at which point it becomes a complete type.
> > > > > > > >
> > > > > > > > So the conversion is ill-formed.
> > > > > > > >
> > > > > > > > Jason
> > > > > > >
> > > > > > > But the conversion in the example (in
> > > > > > > decltype(__test_aux<_To1>(declval<_From1>())))
> > > > > > > is in a SFINAE context, so shouldn't it gracefully fall back to the
> > > > > > > `(...)` overload?
> > > > > >
> > > > > > I think so, and clang++ and icc also compile the testcase fine (and we used to
> > > > > > too, before r159006).
> > > > >
> > > > > Absolutely, the conversion being ill-formed means substitution fails, and we
> > > > > reject that candidate.  I meant that we shouldn't get as far as
> > > > > type_promotes_to for an incomplete type.
> > > >
> > > > Makes sense.  So here's another attempt:
> > > >
> > > > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> > > >
> > > > 2019-01-25  Marek Polacek  <polacek@redhat.com>
> > > >
> > > >         PR c++/89024 - ICE with incomplete enum type.
> > > >         * call.c (standard_conversion): When converting an
> > > >         ARITHMETIC_TYPE_P to an incomplete type, return NULL.
> > >
> > > OK.
> > >
> >
> > Hi,
> > The new test fails on arm-eabi (with newlib, but passes on on arm*linux*):
> > FAIL: g++.dg/cpp0x/enum37.C  -std=c++14 (test for excess errors)
> > FAIL: g++.dg/cpp0x/enum37.C  -std=c++17 (test for excess errors)
> >
> > The log says:
> > /gcc/testsuite/g++.dg/cpp0x/enum37.C:24:41: error: aggregate
> > 'same<unsigned int, unsigned char> s2' has incomplete type and cannot
> > be defined

I imagine that this is because arm-eabi defaults to -fshort-enums; you
can check for this in the testsuite with { target short_enums }.

> Clearly the additional checking I added won't fly; Jason, can I commit
> this?
>
> Tested on x86_64-linux, ok for trunk?
>
> 2019-01-28  Marek Polacek  <polacek@redhat.com>
>
>         * g++.dg/cpp0x/enum37.C: Remove a check.

I'd prefer to make the check conditional.

Jason