SERVER-19720 add a std::error_category() for MongoDB error codes

src/mongo/base/SConscript

@@ -25,5 +25,29 @@ env.CppUnitTest('base_test',
                  'parse_number_test.cpp',
                  'status_test.cpp',
                  'status_with_test.cpp',
-                 'string_data_test.cpp'
+                 'string_data_test.cpp',
                 ])
+
+env.Library(
+    target=[
+        'system_error'
+    ],
+    source=[
+        'system_error.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/base',
+    ],
+)
+
+env.CppUnitTest(
+    target=[
+        'system_error_test',
+    ],
+    source=[
+        'system_error_test.cpp',
+    ],
+    LIBDEPS=[
+        'system_error',
+    ],
+)

src/mongo/base/system_error.cpp

@@ -0,0 +1,91 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include <boost/config.hpp>
+#include <string>
+
+#include "mongo/base/system_error.h"
+
+namespace mongo {
+
+namespace {
+
+/**
+ * A std::error_category for the codes in the named ErrorCodes space.
+ */
+class MongoErrorCategoryImpl final : public std::error_category {
+public:
+    MongoErrorCategoryImpl() = default;
+
+    const char* name() const noexcept override {
+        return "mongo";
+    }
+
+    std::string message(int ev) const override {
+        return ErrorCodes::errorString(ErrorCodes::fromInt(ev));
+    }
+
+    // We don't really want to override this function, but to override the second we need to,
+    // otherwise there will be issues with overload resolution. Additionally, the use of
+    // BOOST_NOEXCEPT is necessitated by the libc++/libstdc++ STL having 'noexcept' on the
+    // overridden methods, but not the Dinkumware STL as of MSVC 2013.
+    bool equivalent(const int code,
+                    const std::error_condition& condition) const BOOST_NOEXCEPT override {
+        return std::error_category::equivalent(code, condition);
+    }
+
+    bool equivalent(const std::error_code& code, int condition) const BOOST_NOEXCEPT override {
+        switch (ErrorCodes::fromInt(condition)) {
+            case ErrorCodes::OK:
+                // Make ErrorCodes::OK to be equivalent to the default constructed error code.
+                return code == std::error_code();
+            default:
+                return false;
+        }
+    }
+};
+
+}  // namespace
+
+const std::error_category& mongoErrorCategory() {
+    // TODO: Remove this static, and make a constexpr instance when we move to C++14.
+    const static MongoErrorCategoryImpl instance{};
+    return instance;
+}
+
+std::error_code make_error_code(ErrorCodes::Error code) {
+    return std::error_code(ErrorCodes::fromInt(code), mongoErrorCategory());
+}
+
+std::error_condition make_error_condition(ErrorCodes::Error code) {
+    return std::error_condition(ErrorCodes::fromInt(code), mongoErrorCategory());
+}
+
+}  // namespace mongo

src/mongo/base/system_error.h

@@ -0,0 +1,57 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <system_error>
+#include <type_traits>
+
+#include "mongo/base/error_codes.h"
+
+namespace mongo {
+
+const std::error_category& mongoErrorCategory();
+
+// The next two functions are explicitly named (contrary to our naming style) so that they can be
+// picked up by ADL.
+std::error_code make_error_code(ErrorCodes::Error code);
+
+std::error_condition make_error_condition(ErrorCodes::Error code);
+
+}  // namespace mongo
+
+namespace std {
+
+/**
+ * Allows a std::error_condition to be implicitly constructed from a mongo::ErrorCodes::Error.
+ * We specialize this instead of is_error_code_enum as our ErrorCodes are platform independent.
+ */
+template <>
+struct is_error_condition_enum<mongo::ErrorCodes::Error> : public true_type {};
+
+}  // namespace std

src/mongo/base/system_error_test.cpp

@@ -0,0 +1,63 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include <system_error>
+
+#include "mongo/base/system_error.h"
+#include "mongo/unittest/unittest.h"
+
+namespace mongo {
+namespace {
+
+TEST(SystemError, Category) {
+    ASSERT(make_error_code(ErrorCodes::AuthenticationFailed).category() == mongoErrorCategory());
+    ASSERT(std::error_code(ErrorCodes::AlreadyInitialized, mongoErrorCategory()).category() ==
+           mongoErrorCategory());
+    ASSERT(make_error_condition(ErrorCodes::AuthenticationFailed).category() ==
+           mongoErrorCategory());
+    ASSERT(std::error_condition(ErrorCodes::AuthenticationFailed).category() ==
+           mongoErrorCategory());
+}
+
+TEST(SystemError, Conversions) {
+    ASSERT(make_error_code(ErrorCodes::AlreadyInitialized) == ErrorCodes::AlreadyInitialized);
+    ASSERT(std::error_code(ErrorCodes::AlreadyInitialized, mongoErrorCategory()) ==
+           ErrorCodes::AlreadyInitialized);
+    ASSERT(make_error_condition(ErrorCodes::AlreadyInitialized) == ErrorCodes::AlreadyInitialized);
+    ASSERT(std::error_condition(ErrorCodes::AlreadyInitialized) == ErrorCodes::AlreadyInitialized);
+}
+
+TEST(SystemError, Equivalence) {
+    ASSERT(ErrorCodes::OK == std::error_code());
+    ASSERT(std::error_code() == ErrorCodes::OK);
+}
+
+}  // namespace
+}  // namespace mongo