Bootstrapped and regtested on x86_64-pc-linuxgnu, does this look
OK for trunk? Sadly the prerequisity patch r15-2331-g523836716137d0
probably isn't suitable for backporting, so I reckon this should be
trunk-only.
-- >8 --
Here we're prematurely stripping the decltype(lambda) alias used inside
the template-id during ahead of time template argument coercion, which
means we treat it as if it were
is_same_v<decltype([]{}), decltype([]{})>
which instead yields false since now we're substituting into the lambda
twice, and every such substitution yields a unique lambda. This
demonstrates that such aliases should be considered opaque, a notion which
coincidentally we recently introduced in r15-2331-g523836716137d0.
PR c++/116714
gcc/cp/ChangeLog:
* pt.cc (dependent_opaque_alias_p): Also return true for a
decltype(lambda) alias.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/lambda-uneval18.C: New test.
---
gcc/cp/pt.cc | 6 ++++--
gcc/testsuite/g++.dg/cpp2a/lambda-uneval18.C | 20 ++++++++++++++++++++
2 files changed, 24 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-uneval18.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 04987f66746..a72a1eadbc7 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -6764,8 +6764,10 @@ dependent_opaque_alias_p (const_tree t)
{
return (TYPE_P (t)
&& typedef_variant_p (t)
- && any_dependent_type_attributes_p (DECL_ATTRIBUTES
- (TYPE_NAME (t))));
+ && (any_dependent_type_attributes_p (DECL_ATTRIBUTES
+ (TYPE_NAME (t)))
+ || (TREE_CODE (t) == DECLTYPE_TYPE
+ && TREE_CODE (DECLTYPE_TYPE_EXPR (t)) == LAMBDA_EXPR)));
}
/* Return the number of innermost template parameters in TMPL. */
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-uneval18.C
b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval18.C
new file mode 100644
index 00000000000..2942f8305c7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval18.C
@@ -0,0 +1,20 @@
+// PR c++/116714
+// { dg-do compile { target c++20 } }
+
+template<class T, class U>
+inline constexpr bool is_same_v = __is_same(T, U);
+
+template<class T, class U>
+struct is_same { static constexpr bool value = false; };
+
+template<class T>
+struct is_same<T, T> { static constexpr bool value = true; };
+
+template<class>
+void f() {
+ using type = decltype([]{});
+ static_assert(is_same_v<type, type>);
+ static_assert(is_same<type, type>::value);
+};
+
+template void f<int>();
--
2.46.1.506.ged155187b4
