On Wed, Jan 28, 2026 at 05:10:18PM -0500, Marek Polacek wrote:
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>
> -- >8 --
> As discussed in
> <https://gcc.gnu.org/pipermail/gcc-patches/2026-January/705756.html>,
> we should check TYPE_BEING_DEFINED along with COMPLETE_TYPE_P in
> eval_define_aggregate. It seems that with this check added, we don't
> need this code anymore:
>
> if (c == type)
> {
> auto_diagnostic_group d;
> error_at (loc, "%<define_aggregate%> evaluated from "
> "%<consteval%> block enclosed by %qT being "
> "defined", type);
> //...
> }
>
> but I'm not removing that in this patch.
>
> gcc/cp/ChangeLog:
>
> * reflect.cc (eval_define_aggregate): Also give an error when
> TYPE_BEING_DEFINED is true for the first argument.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/reflect/define_aggregate3.C: Adjust expected diagnostic.
> * g++.dg/reflect/p2996-21.C: Likewise.
> ---
> gcc/cp/reflect.cc | 8 ++++++++
> gcc/testsuite/g++.dg/reflect/define_aggregate3.C | 16 ++++++++--------
> gcc/testsuite/g++.dg/reflect/p2996-21.C | 4 ++--
> 3 files changed, 18 insertions(+), 10 deletions(-)
>
> diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc
> index bdeec2f0f38..4845e648fdf 100644
> --- a/gcc/cp/reflect.cc
> +++ b/gcc/cp/reflect.cc
> @@ -5896,6 +5896,14 @@ eval_define_aggregate (location_t loc, const
> constexpr_ctx *ctx,
> *non_constant_p = true;
> return call;
> }
> + if (TYPE_BEING_DEFINED (type))
> + {
> + if (!cxx_constexpr_quiet_p (ctx))
> + error_at (loc, "first %<define_aggregate%> argument is a reflection "
> + "of a class type being defined");
I wonder if this message shouldn't mention the type like the diagnostics
that is obsoleted by this.
While in cases like S3 it is obvious, sometimes the define_aggregate might
be in a consteval call with completely different locus and figuring out
what is the type being defined might be harder.
> + *non_constant_p = true;
> + return call;
> + }
> hash_set<tree> nameset;
> for (int i = 0; i < TREE_VEC_LENGTH (rvec); ++i)
> {
> diff --git a/gcc/testsuite/g++.dg/reflect/define_aggregate3.C
> b/gcc/testsuite/g++.dg/reflect/define_aggregate3.C
> index db04a80bbe3..382194ff727 100644
> --- a/gcc/testsuite/g++.dg/reflect/define_aggregate3.C
> +++ b/gcc/testsuite/g++.dg/reflect/define_aggregate3.C
> @@ -15,8 +15,8 @@ consteval bool foo () { return define_aggregate (^^S2, {})
> == ^^S2; }
> const bool a = foo (); // { dg-error
> "call to consteval function 'foo\\\(\\\)' is not a constant expression" }
>
> struct S3 {
> - consteval { // { dg-message
> "'consteval' block defined here" }
> - define_aggregate (^^S3, {}); // { dg-error
> "'define_aggregate' evaluated from 'consteval' block enclosed by 'S3' being
> defined" }
> + consteval {
> + define_aggregate (^^S3, {}); // { dg-error "first
> 'define_aggregate' argument is a reflection of a class type being defined" }
> }
> };
>
> @@ -33,26 +33,26 @@ consteval {
>
> template <typename T>
> struct S5 {
> - consteval { // { dg-message
> "'consteval' block defined here" }
> - define_aggregate (^^S5 <T>, {}); // { dg-error
> "'define_aggregate' evaluated from 'consteval' block enclosed by 'S5<int>'
> being defined" }
> + consteval {
> + define_aggregate (^^S5 <T>, {}); // { dg-error "first
> 'define_aggregate' argument is a reflection of a class type being defined" }
> }
> };
>
> S5 <int> s5;
>
> -consteval bool bar (info x) { return define_aggregate (x, {}) == x; }
> // { dg-error "'define_aggregate' evaluated from 'consteval' block enclosed
> by 'S6' being defined" }
> +consteval bool bar (info x) { return define_aggregate (x, {}) == x; }
> // { dg-error "first 'define_aggregate' argument is a reflection of a class
> type being defined" }
>
> struct S6 {
> - consteval { // { dg-message
> "'consteval' block defined here" }
> + consteval {
> bar (^^S6);
> }
> };
>
> -consteval bool baz (info x) { return define_aggregate (x, {}) == x; }
> // { dg-error "'define_aggregate' evaluated from 'consteval' block enclosed
> by 'S7<char>' being defined" }
> +consteval bool baz (info x) { return define_aggregate (x, {}) == x; }
> // { dg-error "first 'define_aggregate' argument is a reflection of a class
> type being defined" }
>
> template <typename T>
> struct S7 {
> - consteval { // { dg-message
> "'consteval' block defined here" }
> + consteval {
> baz (^^S7 <T>);
> }
> };
> diff --git a/gcc/testsuite/g++.dg/reflect/p2996-21.C
> b/gcc/testsuite/g++.dg/reflect/p2996-21.C
> index 8a9f7895d59..46d235afb01 100644
> --- a/gcc/testsuite/g++.dg/reflect/p2996-21.C
> +++ b/gcc/testsuite/g++.dg/reflect/p2996-21.C
> @@ -7,9 +7,9 @@
> using namespace std::meta;
>
> struct S0 {
> - consteval { // { dg-message
> "'consteval' block defined here" }
> + consteval {
> std::meta::define_aggregate(^^S0, {}); // error: scope
> associated with S0 encloses the consteval block
> - } // { dg-error
> "'define_aggregate' evaluated from 'consteval' block enclosed by 'S0' being
> defined" "" { target *-*-* } .-1 }
> + } // { dg-error "first
> 'define_aggregate' argument is a reflection of a class type being defined" ""
> { target *-*-* } .-1 }
> };
>
> struct S1;
>
> base-commit: a1adc5aa30caae043cbd45dbbf9a738bebba34cc
> --
> 2.52.0
Jakub
