[PATCH] PR libstdc++/90220 Fix std::any_cast for function pointers

[Jonathan Wakely]

        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.
        * testsuite/20_util/any/misc/any_cast.cc: Test std::any_cast with
        function types.

Tested powerpc64le-linux, committed to trunk.

The PR describes two bugs in any_cast, but I might leave the fix for
the other part until stage 1.


commit 1da13522c390bcb2bf70348656116a4d034aa9a6
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed Apr 24 10:05:30 2019 +0100

    PR libstdc++/90220 Fix std::any_cast for function pointers
    
            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.
            * testsuite/20_util/any/misc/any_cast.cc: Test std::any_cast with
            function types.

diff --git a/libstdc++-v3/include/std/any b/libstdc++-v3/include/std/any
index b0553dccf22..792db27b061 100644
--- a/libstdc++-v3/include/std/any
+++ b/libstdc++-v3/include/std/any
@@ -532,16 +532,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _ValueType>
     inline const _ValueType* any_cast(const any* __any) noexcept
     {
-      if (__any)
-       return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
+      if constexpr (is_object_v<_ValueType>)
+       if (__any)
+         return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
       return nullptr;
     }
 
   template<typename _ValueType>
     inline _ValueType* any_cast(any* __any) noexcept
     {
-      if (__any)
-       return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
+      if constexpr (is_object_v<_ValueType>)
+       if (__any)
+         return static_cast<_ValueType*>(__any_caster<_ValueType>(__any));
       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 8f19dc3ae0b..c9aeaae3366 100644
--- a/libstdc++-v3/testsuite/20_util/any/misc/any_cast.cc
+++ b/libstdc++-v3/testsuite/20_util/any/misc/any_cast.cc
@@ -20,6 +20,7 @@
 
 #include <any>
 #include <string>
+#include <utility>
 #include <cstring>
 #include <testsuite_hooks.h>
 
@@ -121,6 +122,38 @@ void test05()
   VERIFY( p == nullptr );
 }
 
+void test06()
+{
+  // The contained value of a std::any is always an object type,
+  // but std::any_cast does not forbid checking for function types.
+
+  any a(1);
+  void (*p1)() = any_cast<void()>(&a);
+  VERIFY( p1 == nullptr );
+  int (*p2)(int) = any_cast<int(int)>(&a);
+  VERIFY( p2 == nullptr );
+  int (*p3)() = any_cast<int()>(&std::as_const(a));
+  VERIFY( p3 == nullptr );
+
+  try {
+    any_cast<int(&)()>(a);
+    VERIFY( false );
+  } catch (const std::bad_any_cast&) {
+  }
+
+  try {
+    any_cast<int(&)()>(std::move(a));
+    VERIFY( false );
+  } catch (const std::bad_any_cast&) {
+  }
+
+  try {
+    any_cast<int(&)()>(std::as_const(a));
+    VERIFY( false );
+  } catch (const std::bad_any_cast&) {
+  }
+}
+
 int main()
 {
   test01();
@@ -128,4 +161,5 @@ int main()
   test03();
   test04();
   test05();
+  test06();
 }