Re: [PATCH] c++, v4: implement C++29 P2287R6 - Designated-initializers for Base Classes [PR125989]

On 8/5/26 7:11 AM, Jakub Jelinek wrote:
> On Tue, Aug 04, 2026 at 09:46:21PM -0400, Jason Merrill wrote:
>> Nice.
>>
>> But it seems to me that once we cache the lookups this way, we don't need to
>> determine the set of designators that belong to the current base; we should
>> be able to look them all up and let the normal handling work from there.
>>
>> I felt awkward about continuing to ask you for changes, so I poked at it
>> some myself.  The first patch changes reshape_init_class to avoid changing
>> d->end, and I think makes sense to combine with your patch.
> 
> Thanks.  I've looked at your first patch and it looks correct to me and indeed
> simplifies stuff.
> 
>> It would also be good to check -Wmissing-braces in at least one of the new
>> testcases.
> 
> I've added -Wmissing-braces coverage into desig14.C now, see incremental
> diff here and attached full patch (my last patch + your simplify patch
> + this incremental).
> So far tested with
> GXX_TESTSUITE_STDS=98,11,14,17,20,23,26,29 make check-g++ RUNTESTFLAGS="dg.exp='desig* feat-cxx29.C pr43765.C embed-14.C'"
> together, ok for trunk if it passes full bootstrap/regtest?

OK, thanks.

>> The second patch changes _class to go through reshape_init_r for this case
>> instead of directly recursing into reshape_init_class, which avoids the
>> duplication of -Wmissing-braces handling.  This required more adjustment of
>> reshape_init_r than I expected, so I'm inclined to make it a followup, but I
>> think it's a useful clarification.
> 
> Not sure if I understood all the details but I haven't tried much yet.
> If it can go in separately, doesn't have to be done immediately.
> 
> --- gcc/testsuite/g++.dg/cpp29/desig14.C.jj	2026-08-05 12:33:10.574200452 +0200
> +++ gcc/testsuite/g++.dg/cpp29/desig14.C	2026-08-05 12:57:26.171939454 +0200
> @@ -1,14 +1,23 @@
>   // C++29 P2287R6 - Designated-initializers for Base Classes
>   // { dg-do compile { target c++20 } }
> -// { dg-options "" }
> +// { dg-options "-Wmissing-braces" }
>   
>   struct A { int a, b; };
>   struct B { int c, d; };
>   struct C : A, B { int e, f; };
> +struct D : C { int g; };
>   auto c1 = C { { .a = 1, .b = 2 }, { .c = 3, .d = 4 }, .e = 5, .f = 6 };	// { dg-warning "either all initializer clauses should be designated or none of them should be" "" { target c++26_down } }
>   auto c2 = C { { .a = 1, .b = 2 }, .e = 5, .f = 6 };			// { dg-warning "either all initializer clauses should be designated or none of them should be" "" { target c++26_down } }
>   auto c3 = C { {}, { .c = 3, .d = 4 }, .f = 6 };				// { dg-warning "either all initializer clauses should be designated or none of them should be" "" { target c++26_down } }
>   auto c4 = C { .e = 1, 2 };						// { dg-error "either all initializer clauses should be designated or none of them should be" "" { target c++26_down } }
>   									// { dg-error "designated initializer clause should not be followed by non-designated" "" { target c++29 } .-1 }
> +auto c5 = C { .a = 1, .b = 2, .c = 3, .d = 4, .e = 5, .f = 6 };		// { dg-error "'C' has no non-static data member named 'a'" "" { target c++26_down } }
> +									// { dg-warning "missing braces around initializer for 'A'" "" { target c++29 } .-1 }
> +									// { dg-warning "missing braces around initializer for 'B'" "" { target c++29 } .-2 }
>   auto a1 = A { 1, .b = 2 };						// { dg-error "last non-designated initializer clause does not appertain to a base class subobject" }
>   									// { dg-warning "either all initializer clauses should be designated or none of them should be" "" { target c++26_down } .-1 }
> +auto d1 = D { .a = 1, .b = 2, .c = 3, .d = 4, .e = 5, .f = 6, .g = 7 };	// { dg-error "'D' has no non-static data member named 'a'" "" { target c++26_down } }
> +									// { dg-warning "missing braces around initializer for 'A'" "" { target c++29 } .-1 }
> +									// { dg-warning "missing braces around initializer for 'B'" "" { target c++29 } .-2 }
> +									// { dg-warning "missing braces around initializer for 'C'" "" { target c++29 } .-3 }
> +auto d2 = D { { { .a = 1, .b = 2 }, { .c = 3, .d = 4 }, .e = 5, .f = 6 }, .g = 7 }; // { dg-warning "either all initializer clauses should be designated or none of them should be" "" { target c++26_down } }
> 
> 
> 	Jakub