PR libstdc++/90220 Fix std::any_cast for array types

Although the std::any constructors use decay_t to determine the type of
the contained value, std::any_cast should use the un-decayed type (and
so always fail for function and array types that decay to pointers).

Using remove_cv_t is correct, because the condition for std::any_cast
to return non-null is operand.type() == typeid(T) and typeid ignores
top-level cv-qualifiers.

	PR libstdc++/90220
	* include/std/any (__any_caster): Use remove_cv_t instead of decay_t.
	Avoid a runtime check for types that can never be stored in std::any.
	* testsuite/20_util/any/misc/any_cast.cc: Test std::any_cast with
	array types.

From-SVN: r270547

3 files changed, 38 insertions, 7 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 8be3dcc..2ab686b 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,11 @@
 2019-04-24  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/90220
+	* include/std/any (__any_caster): Use remove_cv_t instead of decay_t.
+	Avoid a runtime check for types that can never be stored in std::any.
+	* testsuite/20_util/any/misc/any_cast.cc: Test std::any_cast with
+	array types.
+
 	PR libstdc++/90220 (partial)
 	* include/std/any (any_cast<T>(any*), any_cast<T>(const any*)): Do
 	not attempt ill-formed static_cast to pointers to non-object types.
diff --git a/libstdc++-v3/include/std/any b/libstdc++-v3/include/std/any
index 792db27..29fe03e 100644
--- a/libstdc++-v3/include/std/any
+++ b/libstdc++-v3/include/std/any
@@ -506,14 +506,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     void* __any_caster(const any* __any)
     {
-      if constexpr (is_copy_constructible_v<decay_t<_Tp>>)
+      // any_cast<T> returns non-null if __any->type() == typeid(T) and
+      // typeid(T) ignores cv-qualifiers so remove them:
+      using _Up = remove_cv_t<_Tp>;
+      // The contained value has a decayed type, so if decay_t<U> is not U,
+      // then it's not possible to have a contained value of type U:
+      if constexpr (!is_same_v<decay_t<_Up>, _Up>)
+	return nullptr;
+      // Only copy constructible types can be used for contained values:
+      else if constexpr (!is_copy_constructible_v<_Up>)
+	return nullptr;
+      // This check is equivalent to __any->type() == typeid(_Tp)
+      else if (__any->_M_manager == &any::_Manager<_Up>::_S_manage)
 	{
-	  if (__any->_M_manager == &any::_Manager<decay_t<_Tp>>::_S_manage)
-	    {
-	      any::_Arg __arg;
-	      __any->_M_manager(any::_Op_access, __any, &__arg);
-	      return __arg._M_obj;
-	    }
+	  any::_Arg __arg;
+	  __any->_M_manager(any::_Op_access, __any, &__arg);
+	  return __arg._M_obj;
 	}
       return nullptr;
     }
diff --git a/libstdc++-v3/testsuite/20_util/any/misc/any_cast.cc b/libstdc++-v3/testsuite/20_util/any/misc/any_cast.cc
index c9aeaae..b7fbbc5 100644
--- a/libstdc++-v3/testsuite/20_util/any/misc/any_cast.cc
+++ b/libstdc++-v3/testsuite/20_util/any/misc/any_cast.cc
@@ -154,6 +154,22 @@ void test06()
   }
 }
 
+void test07()
+{
+  int arr[3];
+  any a(arr);
+  VERIFY( a.type() == typeid(int*) );	// contained value is decayed
+
+  int (*p1)[3] = any_cast<int[3]>(&a);
+  VERIFY( a.type() != typeid(int[3]) ); // so any_cast should return nullptr
+  VERIFY( p1 == nullptr );
+  int (*p2)[] = any_cast<int[]>(&a);
+  VERIFY( a.type() != typeid(int[]) );	// so any_cast should return nullptr
+  VERIFY( p2 == nullptr );
+  const int (*p3)[] = any_cast<int[]>(&std::as_const(a));
+  VERIFY( p3 == nullptr );
+}
+
 int main()
 {
   test01();
@@ -162,4 +178,5 @@ int main()
   test04();
   test05();
   test06();
+  test07();
 }