On 8/3/26 2:23 PM, Marek Polacek wrote:
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/16?
-- >8 --
[expr.reflect] says that a reflection of a pack-index-expressions
is ill-formed. But that applies to the ^^id-expression production,
not ^^type-id, in which a pack-index-specifier (for types) can be
used. So it's wrong for get_reflection to check PACK_INDEX_P, it
should only reject PACK_INDEX_EXPR.
I don't think that currently we can get there with a PACK_INDEX_EXPR
though: for a pack-index-expression Xs...[0] cp_parser_reflection_name
will consume Xs and then immediately call get_reflection which gives
an error.
This seems like a bit of a bug, since "A reflect-expression is parsed as
the longest possible sequence of tokens that could syntactically form a
reflect-expression.", i.e. the full pack-index-expression. But not an
important one, since it's ill-formed either way.
OK for trunk/16.
But leaving the PACK_INDEX_EXPR check in doesn't seem like
a bad idea.
PR c++/126546
gcc/cp/ChangeLog:
* reflect.cc (get_reflection): Check PACK_INDEX_EXPR instead of
PACK_INDEX_P.
gcc/testsuite/ChangeLog:
* g++.dg/reflect/pack-index1.C: Accept a reflection of a
pack-index-specifier. Reject a reflection of a
pack-index-expression.
* g++.dg/reflect/pack-index2.C: New test.
---
gcc/cp/reflect.cc | 2 +-
gcc/testsuite/g++.dg/reflect/pack-index1.C | 9 ++++++++-
gcc/testsuite/g++.dg/reflect/pack-index2.C | 8 ++++++++
3 files changed, 17 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/reflect/pack-index2.C
diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc
index 989d7cebc77..7b4142f2d4f 100644
--- a/gcc/cp/reflect.cc
+++ b/gcc/cp/reflect.cc
@@ -141,7 +141,7 @@ get_reflection (location_t loc, tree t, reflect_kind
kind/*=REFLECT_UNDEF*/)
/* Constant template parameters and pack-index-expressions cannot
appear as operands of the reflection operator. */
- if (PACK_INDEX_P (t))
+ if (TREE_CODE (t) == PACK_INDEX_EXPR)
{
error_at (loc, "%<^^%> cannot be applied to a pack index");
return error_mark_node;
diff --git a/gcc/testsuite/g++.dg/reflect/pack-index1.C
b/gcc/testsuite/g++.dg/reflect/pack-index1.C
index f68705b1299..c2b27a8c133 100644
--- a/gcc/testsuite/g++.dg/reflect/pack-index1.C
+++ b/gcc/testsuite/g++.dg/reflect/pack-index1.C
@@ -14,10 +14,16 @@ f ()
{
constexpr auto r1 = ^^Ts...[0]::sx;
constexpr auto r2 = ^^typename Ts...[0]::type;
+ constexpr auto e = ^^Ts...[0];
+}
+template<int... Ns>
+void
+g ()
+{
// NTTPs and pack-index-expressions cannot appear as operands
// of the reflection operator.
- constexpr auto e = ^^Ts...[0]; // { dg-error "cannot be applied" }
+ constexpr auto e = ^^Ns...[0]; // { dg-error "cannot be applied" }
}
@@ -25,4 +31,5 @@ void
g ()
{
f<S>();
+ g<1, 2, 3>();
}
diff --git a/gcc/testsuite/g++.dg/reflect/pack-index2.C
b/gcc/testsuite/g++.dg/reflect/pack-index2.C
new file mode 100644
index 00000000000..113629510f1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/reflect/pack-index2.C
@@ -0,0 +1,8 @@
+// PR c++/126546
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-freflection" }
+
+template <class... Ts>
+consteval auto first() { return ^^Ts...[0]; }
+
+static_assert(first<int, double>() == ^^int);
base-commit: 71d225bf68f1c5cf31b2e7fd5759b43f8dadc280
