On Fri, Oct 23, 2026 at 01:36:21PM -0400, Jason Merrill wrote:
> On 10/23/26 9:27 AM, Marek Polacek wrote:
> > On Tue, Oct 20, 2026 at 06:08:54PM -0400, Jason Merrill wrote:
> > > On 10/8/26 5:26 PM, Marek Polacek wrote:
> > > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > > >
> > > > -- >8 --
> > > > [expr.prim.splice]/2 doesn't actually allow templates in
> > > > a splice-expression of the form splice-specifier, but we are not
> > > > currently detecting that in check_splice_expr, which can mean
> > > > that we crash if the user attempts to use such a splice.
> > > >
> > > > As an extension, we allow function templates, and assume that the
> > > > user forgot to type 'template'.
> > >
> > > Do we still give a diagnostic by default in that case?
> >
> > No, the missing "expected template keyword" is subject of PR127802.
>
> We could give that diagnostic here?
Yes, that was my plan. I thought I'd do it in a follow-up patch in
case it gets messy. This one was just supposed to fix the ICE. But
if you want both in the same patch, I could do that.
> > > > mangle3.C was testing invalid cases so remove that.
> > > >
> > > > PR c++/125631
> > > >
> > > > gcc/cp/ChangeLog:
> > > >
> > > > * reflect.cc (check_splice_expr): Reject (non-function)
> > > > templates.
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > > * g++.dg/reflect/crash6.C: Adjust dg-error.
> > > > * g++.dg/reflect/mangle3.C: Remove some invalid tests.
> > > > * g++.dg/reflect/error15.C: New test.
> > > > ---
> > > > gcc/cp/reflect.cc | 15 +++++
> > > > gcc/testsuite/g++.dg/reflect/crash6.C | 4 +-
> > > > gcc/testsuite/g++.dg/reflect/error15.C | 84
> > > > ++++++++++++++++++++++++++
> > > > gcc/testsuite/g++.dg/reflect/mangle3.C | 9 ---
> > > > 4 files changed, 101 insertions(+), 11 deletions(-)
> > > > create mode 100644 gcc/testsuite/g++.dg/reflect/error15.C
> > > >
> > > > diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc
> > > > index 8bf518df64f..62c4e168108 100644
> > > > --- a/gcc/cp/reflect.cc
> > > > +++ b/gcc/cp/reflect.cc
> > > > @@ -9362,6 +9362,21 @@ check_splice_expr (location_t loc, location_t
> > > > start_loc, tree t,
> > > > return false;
> > > > }
> > > > + /* [expr.prim.splice]/2 doesn't allow for the splice-expression of
> > > > the form
> > > > + splice-specifier to designate a template. But we accept a
> > > > function
> > > > + template here as an extension, because it would be valid if the
> > > > 'template'
> > > > + keyword were present. */
> > > > + if (!template_p
> > > > + && !targs_p
> > > > + && !member_access_p
> > > > + && TREE_CODE (t) == TEMPLATE_DECL
> > > > + && !DECL_FUNCTION_TEMPLATE_P (t))
> > > > + {
> > > > + if (complain_p)
> > > > + error_at (loc, "cannot use template %qE in a splice
> > > > expression", t);
> > > > + return false;
> > > > + }
> > > > +
> > > > /* [expr.prim.splice]/2: "The expression is ill-formed if S [the
> > > > construct
> > > > designated by splice-specifier] is
> > > > -- a local entity such that there is a lambda scope that
> > > > intervenes
> > > > diff --git a/gcc/testsuite/g++.dg/reflect/crash6.C
> > > > b/gcc/testsuite/g++.dg/reflect/crash6.C
> > > > index a455a61cd65..4dd2f5fc7b8 100644
> > > > --- a/gcc/testsuite/g++.dg/reflect/crash6.C
> > > > +++ b/gcc/testsuite/g++.dg/reflect/crash6.C
> > > > @@ -10,8 +10,8 @@ template<info R>
> > > > void
> > > > f ()
> > > > {
> > > > - [:R:] r; // { dg-error "expected" }
> > > > - [:R:]<int> r; // { dg-error "expected" }
> > > > + [:R:] r; // { dg-error "expected|cannot use template" }
> > > > + [:R:]<int> r; // { dg-error "expected|cannot use template" }
> > > > }
> > > > void
> > > > diff --git a/gcc/testsuite/g++.dg/reflect/error15.C
> > > > b/gcc/testsuite/g++.dg/reflect/error15.C
> > > > new file mode 100644
> > > > index 00000000000..a2fdf4a52ed
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/g++.dg/reflect/error15.C
> > > > @@ -0,0 +1,84 @@
> > > > +// PR c++/125631
> > > > +// { dg-do compile { target c++26 } }
> > > > +// { dg-additional-options "-freflection" }
> > > > +
> > > > +#include <tuple>
> > > > +
> > > > +template<auto Templ, class Tuple>
> > > > +const auto
> > > > +make_from_tuple (Tuple&& t)
> > > > +{
> > > > + return [:Templ:]{}; // { dg-error "expected|cannot use template
> > > > .std::tuple. in a splice expression" }
> > > > +}
> > > > +auto p = make_from_tuple<^^std::tuple>(std::tuple());
> > > > +
> > > > +template<auto N> int tv;
> > > > +template<auto N> concept C = requires { true; };
> > > > +template<typename T> struct S { };
> > > > +template<typename T>
> > > > +using A = S<T>;
> > > > +template<typename> using I = int;
> > > > +
> > > > +template<auto R>
> > > > +void
> > > > +g1 ()
> > > > +{
> > > > + auto a = [:R:]; // { dg-error "cannot use template .tv<N>. in a
> > > > splice expression" }
> > > > +}
> > > > +
> > > > +template<auto R>
> > > > +void
> > > > +g2 ()
> > > > +{
> > > > + auto a = [:R:]; // { dg-error "cannot use template .C. in a splice
> > > > expression" }
> > > > +}
> > > > +
> > > > +template<auto R>
> > > > +void
> > > > +g3 ()
> > > > +{
> > > > + auto a = [:R:]; // { dg-error "cannot use template .S. in a splice
> > > > expression" }
> > > > +}
> > > > +
> > > > +template<auto R>
> > > > +void
> > > > +g4 ()
> > > > +{
> > > > + auto a = [:R:]; // { dg-error "cannot use template .A. in a splice
> > > > expression" }
> > > > +}
> > > > +
> > > > +template<auto R>
> > > > +void
> > > > +g5 ()
> > > > +{
> > > > + auto a = [:R:]; // { dg-error "cannot use template .I. in a splice
> > > > expression" }
> > > > +}
> > > > +
> > > > +template<template<class> class TT>
> > > > +void
> > > > +g6 ()
> > > > +{
> > > > + auto x = [:^^TT:]; // { dg-error "cannot use template .S. in a
> > > > splice expression" }
> > > > +}
> > > > +
> > > > +template<auto R>
> > > > +void
> > > > +g7 ()
> > > > +{
> > > > + &[:R:]; // { dg-error "cannot use template .S. in a splice
> > > > expression" }
> > > > +}
> > > > +
> > > > +template<auto R> auto g8 () -> decltype([:R:]); // { dg-error
> > > > "cannot use template .tv<N>. in a splice expression" }
> > > > +
> > > > +void
> > > > +h ()
> > > > +{
> > > > + g1<^^tv>();
> > > > + g2<^^C>();
> > > > + g3<^^S>();
> > > > + g4<^^A>();
> > > > + g5<^^I>();
> > > > + g6<S>();
> > > > + g7<^^S>();
> > > > + g8<^^tv>(); // { dg-error "no matching function" }
> > > > +}
> > > > diff --git a/gcc/testsuite/g++.dg/reflect/mangle3.C
> > > > b/gcc/testsuite/g++.dg/reflect/mangle3.C
> > > > index 390f249fb0c..1e1302d1377 100644
> > > > --- a/gcc/testsuite/g++.dg/reflect/mangle3.C
> > > > +++ b/gcc/testsuite/g++.dg/reflect/mangle3.C
> > > > @@ -15,8 +15,6 @@ using Alias = int;
> > > > template<auto>
> > > > struct TCls { };
> > > > -template <auto> int TVar;
> > > > -
> > > > template<typename T>
> > > > struct B {
> > > > T t;
> > > > @@ -41,7 +39,6 @@ namespace N {
> > > > }
> > > > namespace NSAlias = N;
> > > > -template <auto> concept Concept = requires { true; };
> > > > constexpr auto ctx = std::meta::access_context::current ();
> > > > template<typename T>
> > > > @@ -160,18 +157,12 @@ g (int p)
> > > > // { dg-final { scan-assembler "_Z2f4ILDmsb2a1EE4TClsIXszDST_EEEv" }
> > > > }
> > > > f4<^^A>();
> > > > // { dg-final { scan-assembler
> > > > "_Z2f4ILDmen4Enum1AEE4TClsIXszDST_EEEv" } }
> > > > - f4<^^TVar>();
> > > > -// { dg-final { scan-assembler "_Z2f4ILDmvt4TVarEE4TClsIXszDST_EEEv" }
> > > > }
> > > > f5<^^i>();
> > > > // { dg-final { scan-assembler "_Z2f5ILDmvr1iEEDtDST_EEv" } }
> > > > f5<^^a1>();
> > > > // { dg-final { scan-assembler "_Z2f5ILDmsb2a1EEDtDST_EEv" } }
> > > > f5<^^A>();
> > > > // { dg-final { scan-assembler "_Z2f5ILDmen4Enum1AEEDtDST_EEv" } }
> > > > - f5<^^TVar>();
> > > > -// { dg-final { scan-assembler "_Z2f5ILDmvt4TVarEEDtDST_EEv" } }
> > > > - f5<^^Concept>();
> > > > -// { dg-final { scan-assembler "_Z2f5ILDmco7ConceptEEDtDST_EEv" } }
> > > > f5<^^p>();
> > > > // { dg-final { scan-assembler "_Z2f5ILDmvrZ1giE1pEEDtDST_EEv" } }
> > > > f5<std::meta::reflect_constant (42)>();
> > > >
> > > > base-commit: 9b2bbe9104aef2e6bd9e8d7ace5fed3e2726f4d3
Marek
