On Wed, May 06, 2026 at 04:47:09PM -0400, Jason Merrill wrote:
> On 4/22/26 1:36 PM, Marek Polacek wrote:
> > On Tue, Apr 21, 2026 at 05:20:02PM -0400, Jason Merrill wrote:
> > > On 4/21/26 4:21 PM, Marek Polacek wrote:
> > > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > > >
> > > > -- >8 --
> > > > wrapup_namespace_globals gives errors for code like
> > > >
> > > > extern inline int i;
> > > > int &r = i; // odr-used inline variable is not defined
> > > >
> > > > but because we mark consteval-only vars DECL_EXTERNAL, we also wrongly
> > > > emit the error for:
> > > >
> > > > inline constexpr info value{};
> > > > static_assert(value == info{});
> > > >
> > > > where value clearly is defined. ISTM that we should check
> > > > !consteval_only_p
> > > > before giving this error because the test where this could trigger:
> > > >
> > > > extern constexpr inline info x;
> > > >
> > > > is already ill-formed ("declaration of 'constexpr' variable 'x' is not
> > > > a definition").
> > > >
> > > > PR c++/124770
> > > >
> > > > gcc/cp/ChangeLog:
> > > >
> > > > * decl.cc (wrapup_namespace_globals): Don't give the odr-used
> > > > inline variable error for consteval-only variables.
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > > * g++.dg/reflect/init18.C: New test.
> > > > ---
> > > > gcc/cp/decl.cc | 6 +++++-
> > > > gcc/testsuite/g++.dg/reflect/init18.C | 14 ++++++++++++++
> > > > 2 files changed, 19 insertions(+), 1 deletion(-)
> > > > create mode 100644 gcc/testsuite/g++.dg/reflect/init18.C
> > > >
> > > > diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> > > > index 679a8007ca6..7837e322d17 100644
> > > > --- a/gcc/cp/decl.cc
> > > > +++ b/gcc/cp/decl.cc
> > > > @@ -1024,7 +1024,11 @@ wrapup_namespace_globals ()
> > > > if (VAR_P (decl)
> > > > && DECL_EXTERNAL (decl)
> > > > && DECL_INLINE_VAR_P (decl)
> > > > - && DECL_ODR_USED (decl))
> > > > + && DECL_ODR_USED (decl)
> > > > + /* We mark consteval-only vars extern, but they also have
> > > > to be
> > > > + declared constexpr and "extern constexpr inline info
> > > > x;" is
> > > > + ill-formed. */
> > > > + && !consteval_only_p (decl))
> > >
> > > Would it work to check DECL_THIS_EXTERN instead, so we're complaining
> > > about
> > > an extern declaration rather than just based on the compiler deciding not
> > > to
> > > emit?
> >
> > Sadly, no, we'd give the error for
> >
> > extern constexpr inline info v2{};
> > static_assert(v2 == info{});
> >
> > where the extern is I think redundant due to [basic.link]/3.2.3.
> > EDG and clang++ accept that code too.
>
> Ah, true, but DECL_THIS_EXTERN && !DECL_INITIAL ought to work?
It does! v2 here.
> (decl_defined_p could also use refinement)
Like this? (I can send it separately.)
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -5324,7 +5324,9 @@ decl_defined_p (tree decl)
else
{
gcc_assert (VAR_P (decl));
- return !DECL_EXTERNAL (decl);
+ return (!DECL_EXTERNAL (decl)
+ /* extern constexpr inline T foo{}; is a definition. */
+ || (DECL_THIS_EXTERN (decl) && DECL_INITIAL (decl)));
}
}
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/16.2?
-- >8 --
wrapup_namespace_globals gives errors for code like
extern inline int i;
int &r = i; // odr-used inline variable is not defined
but because we mark consteval-only vars DECL_EXTERNAL, we also wrongly
emit the error for:
inline constexpr info value{};
static_assert(value == info{});
where value clearly is defined. This patch strenghtens the check to
also check DECL_THIS_EXTERN && !DECL_INITIAL. We can't only check
the former because
extern constexpr inline info v2{};
is OK.
PR c++/124770
gcc/cp/ChangeLog:
* decl.cc (wrapup_namespace_globals): Give the odr-used
inline variable error for DECL_THIS_EXTERN variables only.
gcc/testsuite/ChangeLog:
* g++.dg/reflect/init18.C: New test.
---
gcc/cp/decl.cc | 7 +++++++
gcc/testsuite/g++.dg/reflect/init18.C | 14 ++++++++++++++
2 files changed, 21 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/reflect/init18.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index f8e9223e43e..4f59fab5e89 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -1023,6 +1023,13 @@ wrapup_namespace_globals ()
if (VAR_P (decl)
&& DECL_EXTERNAL (decl)
+ /* We mark consteval-only variables DECL_EXTERNAL, so check for
+ an explicit extern... */
+ && DECL_THIS_EXTERN (decl)
+ /* ...but
+ extern constexpr inline std::meta::info i{};
+ is a definition (the extern in redundant). */
+ && !DECL_INITIAL (decl)
&& DECL_INLINE_VAR_P (decl)
&& DECL_ODR_USED (decl))
error_at (DECL_SOURCE_LOCATION (decl),
diff --git a/gcc/testsuite/g++.dg/reflect/init18.C
b/gcc/testsuite/g++.dg/reflect/init18.C
new file mode 100644
index 00000000000..f13125be66e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/reflect/init18.C
@@ -0,0 +1,14 @@
+// PR c++/124770
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-freflection" }
+
+using info = decltype(^^::);
+
+constexpr inline info v{};
+static_assert(v == info{});
+extern constexpr inline info v2{};
+static_assert(v2 == info{});
+constexpr inline info v3;
+static_assert(v3 == info{});
+
+extern constexpr inline info v4; // { dg-error "not a
definition|consteval-only" }
base-commit: e8aa21caed8a3c8b4b27d224a04296f008bcf3da
--
2.54.0
