<any>: Short-cut constraints of single-argument any constructor, again

stl/inc/any

@@ -130,10 +130,13 @@ public:
         _Move_from(_That);
     }
 
-    template <class _ValueType, enable_if_t<conjunction_v<negation<is_same<decay_t<_ValueType>, any>>,
-                                                negation<_Is_specialization<decay_t<_ValueType>, in_place_type_t>>,
-                                                is_copy_constructible<decay_t<_ValueType>>>,
-                                    int> = 0>
+    template <class _ValueType,
+        enable_if_t<!is_same_v<decay_t<_ValueType>, any> && !_Is_specialization_v<decay_t<_ValueType>, in_place_type_t>,
+            int> = 0, // Separate these conditions into two `enable_if_t`s to avoid meta-recursion.
+                      // See LLVM-176877 and GH-6109. N5032 [temp.deduct.general]/7 guarantees:
+                      // "The substitution proceeds in lexical order and stops when
+                      // a condition that causes deduction to fail is encountered."
+        enable_if_t<is_copy_constructible_v<decay_t<_ValueType>>, int> = 0>
     any(_ValueType&& _Value) { // initialize with _Value
         _Emplace<decay_t<_ValueType>>(_STD forward<_ValueType>(_Value));
     }

tests/libcxx/expected_results.txt

@@ -1112,9 +1112,6 @@ std/input.output/file.streams/fstreams/filebuf.virtuals/xsputn.pass.cpp:1 FAIL
 std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.pass.cpp:0 FAIL
 std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.pass.cpp:1 FAIL
 
-# Not analyzed. Clang error: no member named 'value' in 'std::is_copy_constructible<ConvertibleFromAndToAny>'
-std/utilities/any/any.class/any.cons/value.pass.cpp:2 FAIL
-
 # Not analyzed. Assertion failed: globalMemCounter.checkOutstandingNewLessThanOrEqual(1)
 std/input.output/filesystems/class.path/path.member/path.assign/move.pass.cpp FAIL
 std/input.output/filesystems/class.path/path.member/path.construct/move.pass.cpp FAIL

tests/std/tests/P0220R1_any/test.cpp

@@ -1040,6 +1040,7 @@ int run_test()
 
 #include <any>
 #include <cassert>
+#include <type_traits>
 
 #include "any_helpers.h"
 #include "count_new.h"
@@ -1160,15 +1161,34 @@ void test_sfinae_constraints() {
     }
 }
 
+// https://llvm.org/PR176877
+// Avoid constraint meta-recursion for a type both convertible from and to std::any.
+template <class T, bool = std::is_copy_constructible<T>::value>
+void test_default_template_argument_is_copy_constructible(T) {}
+
+template <class T, bool = std::is_copy_constructible_v<T>>
+void test_default_template_argument_is_copy_constructible_v(T) {}
+
+void test_no_constraint_recursion() {
+  struct ConvertibleFromAndToAny {
+    ConvertibleFromAndToAny(std::any) {}
+  };
+
+  ConvertibleFromAndToAny src = std::any{};
+  test_default_template_argument_is_copy_constructible(src);
+  test_default_template_argument_is_copy_constructible_v(src);
+}
+
 int run_test() {
     test_copy_move_value<small>();
     test_copy_move_value<large>();
     test_copy_value_throws<small_throws_on_copy>();
     test_copy_value_throws<large_throws_on_copy>();
     test_move_value_throws();
     test_sfinae_constraints();
+    test_no_constraint_recursion();
 
-  return 0;
+    return 0;
 }
 } // namespace ctor::value
 // -- END: test/std/utilities/any/any.class/any.cons/value.pass.cpp