libstdc++: Find make_error_code and make_error_condition via ADL only

The new proposed resolution for LWG 3629 says that std::error_code and
std::error_condition should only use ADL to find their customization
points. This means we need to use a poison pill to prevent lookup from
finding overloads in the enclosing namespaces.

We can also remove the forward declarations of std::make_error_code and
std::make_error_condition, because they aren't needed now. ADL can find
them anyway (when std is an associated namespace), and unqualified name
lookup will not (and should not) find them.

libstdc++-v3/ChangeLog:

	* include/std/system_error (__adl_only::make_error_code): Add
	deleted function.
	(__adl_only::make_error_condition): Likewise.
	(error_code::error_code(ErrorCodeEnum)): Add using-declaration
	for deleted function.
	(error_condition::error_condition(ErrorConditionEnum)):
	Likewise.
	* testsuite/19_diagnostics/error_code/cons/lwg3629.cc: New test.
	* testsuite/19_diagnostics/error_condition/cons/lwg3629.cc: New test.

3 files changed, 109 insertions, 5 deletions

diff --git a/libstdc++-v3/include/std/system_error b/libstdc++-v3/include/std/system_error
index 0504394..e12bb2f 100644
--- a/libstdc++-v3/include/std/system_error
+++ b/libstdc++-v3/include/std/system_error
@@ -195,7 +195,11 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
    * @{
    */
 
-  error_code make_error_code(errc) noexcept;
+namespace __adl_only
+{
+  void make_error_code() = delete;
+  void make_error_condition() = delete;
+}
 
   /** Class error_code
    *
@@ -231,7 +235,10 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
     template<typename _ErrorCodeEnum,
 	     typename = _Check<_ErrorCodeEnum>>
       error_code(_ErrorCodeEnum __e) noexcept
-      { *this = make_error_code(__e); }
+      {
+	using __adl_only::make_error_code;
+	*this = make_error_code(__e);
+      }
 
     error_code(const error_code&) = default;
     error_code& operator=(const error_code&) = default;
@@ -330,8 +337,6 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
     operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
     { return (__os << __e.category().name() << ':' << __e.value()); }
 
-  error_condition make_error_condition(errc) noexcept;
-
   /** Class error_condition
    *
    * This class represents error conditions that may be visible at an API
@@ -363,7 +368,10 @@ _GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
     template<typename _ErrorConditionEnum,
 	     typename = _Check<_ErrorConditionEnum>>
       error_condition(_ErrorConditionEnum __e) noexcept
-      { *this = make_error_condition(__e); }
+      {
+	using __adl_only::make_error_condition;
+	*this = make_error_condition(__e);
+      }
 
     error_condition(const error_condition&) = default;
     error_condition& operator=(const error_condition&) = default;
diff --git a/libstdc++-v3/testsuite/19_diagnostics/error_code/cons/lwg3629.cc b/libstdc++-v3/testsuite/19_diagnostics/error_code/cons/lwg3629.cc
new file mode 100644
index 0000000..b1e0b7f
--- /dev/null
+++ b/libstdc++-v3/testsuite/19_diagnostics/error_code/cons/lwg3629.cc
@@ -0,0 +1,48 @@
+// { dg-do compile { target c++11 } }
+
+// 3629. make_error_code and make_error_condition are customization points
+// Verify that make_error_code is looked up using ADL only.
+
+namespace user
+{
+  struct E1;
+}
+
+// N.B. not in associated namespace of E1, and declared before <system_error>.
+user::E1 make_error_code(user::E1);
+
+#include <future> // declares std::make_error_code(future_errc)
+#include <system_error>
+
+namespace user
+{
+  struct E1
+  {
+    operator std::error_code() const;
+  };
+
+  struct E2
+  {
+    operator std::future_errc() const;
+  };
+
+  struct E3
+  {
+    operator std::errc() const;
+  };
+}
+
+template<> struct std::is_error_code_enum<user::E1> : std::true_type { };
+template<> struct std::is_error_code_enum<user::E2> : std::true_type { };
+template<> struct std::is_error_code_enum<user::E3> : std::true_type { };
+
+// ::make_error_code(E1) should not be found by name lookup.
+std::error_code e1( user::E1{} ); // { dg-error "here" }
+
+// std::make_error_code(errc) should not be found by name lookup.
+std::error_code e2( user::E2{} ); // { dg-error "here" }
+
+// std::make_error_code(future_errc) should not be found by name lookup.
+std::error_code e3( user::E3{} ); // { dg-error "here" }
+
+// { dg-error "use of deleted function" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/19_diagnostics/error_condition/cons/lwg3629.cc b/libstdc++-v3/testsuite/19_diagnostics/error_condition/cons/lwg3629.cc
new file mode 100644
index 0000000..e34b53d
--- /dev/null
+++ b/libstdc++-v3/testsuite/19_diagnostics/error_condition/cons/lwg3629.cc
@@ -0,0 +1,48 @@
+// { dg-do compile { target c++11 } }
+
+// 3629. make_error_code and make_error_condition are customization points
+// Verify that make_error_condition is looked up using ADL only.
+
+namespace user
+{
+  struct E1;
+}
+
+// N.B. not in associated namespace of E1, and declared before <system_error>.
+user::E1 make_error_condition(user::E1);
+
+#include <future> // declares std::make_error_condition(future_errc)
+#include <system_error>
+
+namespace user
+{
+  struct E1
+  {
+    operator std::error_code() const;
+  };
+
+  struct E2
+  {
+    operator std::future_errc() const;
+  };
+
+  struct E3
+  {
+    operator std::errc() const;
+  };
+}
+
+template<> struct std::is_error_condition_enum<user::E1> : std::true_type { };
+template<> struct std::is_error_condition_enum<user::E2> : std::true_type { };
+template<> struct std::is_error_condition_enum<user::E3> : std::true_type { };
+
+// ::make_error_condition(E1) should not be found by name lookup.
+std::error_condition e1( user::E1{} ); // { dg-error "here" }
+
+// std::make_error_condition(errc) should not be found by name lookup.
+std::error_condition e2( user::E2{} ); // { dg-error "here" }
+
+// std::make_error_condition(future_errc) should not be found by name lookup.
+std::error_condition e3( user::E3{} ); // { dg-error "here" }
+
+// { dg-error "use of deleted function" "" { target *-*-* } 0 }