Remove liblo_error error code

Instead define a libloadorder_category error category to identify
libloadorder errors. This allows the libloadorder error code to be
preserved, and is more standard-c++-like.

CMakeLists.txt

@@ -166,6 +166,7 @@ set (LOOT_SRC   "${CMAKE_SOURCE_DIR}/src/backend/app/loot_paths.cpp"
                 "${CMAKE_SOURCE_DIR}/src/backend/app/loot_settings.cpp"
                 "${CMAKE_SOURCE_DIR}/src/backend/app/loot_state.cpp"
                 "${CMAKE_BINARY_DIR}/generated/loot_version.cpp"
+                "${CMAKE_SOURCE_DIR}/src/backend/error_categories.cpp"
                 "${CMAKE_SOURCE_DIR}/src/backend/metadata/condition_evaluator.cpp"
                 "${CMAKE_SOURCE_DIR}/src/backend/metadata/conditional_metadata.cpp"
                 "${CMAKE_SOURCE_DIR}/src/backend/metadata/file.cpp"
@@ -219,6 +220,7 @@ set (LOOT_HEADERS "${CMAKE_SOURCE_DIR}/src/backend/app/loot_paths.h"
                 "${CMAKE_SOURCE_DIR}/src/backend/helpers/yaml_set_helpers.h"
                 "${CMAKE_SOURCE_DIR}/include/loot/api_decorator.h"
                 "${CMAKE_SOURCE_DIR}/include/loot/error.h"
+                "${CMAKE_SOURCE_DIR}/include/loot/error_categories.h"
                 "${CMAKE_SOURCE_DIR}/include/loot/game_type.h"
                 "${CMAKE_SOURCE_DIR}/include/loot/language_code.h"
                 "${CMAKE_SOURCE_DIR}/include/loot/loot_version.h"
@@ -277,6 +279,7 @@ set (LOOT_API_HEADERS "${CMAKE_SOURCE_DIR}/include/loot/api.h"
                       "${CMAKE_SOURCE_DIR}/include/loot/api_decorator.h"
                       "${CMAKE_SOURCE_DIR}/include/loot/database_interface.h"
                       "${CMAKE_SOURCE_DIR}/include/loot/error.h"
+                      "${CMAKE_SOURCE_DIR}/include/loot/error_categories.h"
                       "${CMAKE_SOURCE_DIR}/include/loot/game_type.h"
                       "${CMAKE_SOURCE_DIR}/include/loot/language_code.h"
                       "${CMAKE_SOURCE_DIR}/include/loot/loot_version.h"

docs/api/reference.rst

@@ -48,3 +48,11 @@ Classes
 
 .. doxygenclass:: loot::LootVersion
    :members:
+
+Error Categories
+================
+
+LOOT uses error category objects to identify errors with codes that originate in
+lower-level libraries.
+
+.. doxygenfunction:: loot::libloadorder_category

include/loot/api.h

@@ -31,6 +31,7 @@
 #include "loot/api_decorator.h"
 #include "loot/database_interface.h"
 #include "loot/error.h"
+#include "loot/error_categories.h"
 #include "loot/game_type.h"
 #include "loot/loot_version.h"
 

include/loot/error.h

@@ -46,8 +46,6 @@ public:
      * failed, but its failure was not fatal to the task being performed.
      */
     ok = 0,
-    /** An error was encountered when reading or writing the load order. */
-    liblo_error = 1,
     /** An error was encountered when writing a file. */
     path_write_fail = 2,
     /** An error was encountered when reading a file. */

include/loot/error_categories.h

@@ -0,0 +1,41 @@
+/*  LOOT
+
+    A load order optimisation tool for Oblivion, Skyrim, Fallout 3 and
+    Fallout: New Vegas.
+
+    Copyright (C) 2012-2016    WrinklyNinja
+
+    This file is part of LOOT.
+
+    LOOT is free software: you can redistribute
+    it and/or modify it under the terms of the GNU General Public License
+    as published by the Free Software Foundation, either version 3 of
+    the License, or (at your option) any later version.
+
+    LOOT 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 General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with LOOT.  If not, see
+    <https://www.gnu.org/licenses/>.
+    */
+
+#ifndef LOOT_ERROR_CATEGORIES
+#define LOOT_ERROR_CATEGORIES
+
+#include <system_error>
+
+#include "loot/api_decorator.h"
+
+namespace loot {
+/** @brief Get the error category that can be used to identify system_error
+ *         exceptions that are due to libloadorder errors.
+ *  @returns A reference to the static object of unspecified runtime type,
+             derived from std::error_category.
+ */
+LOOT_API const std::error_category& libloadorder_category();
+}
+
+#endif

src/backend/error_categories.cpp

@@ -0,0 +1,48 @@
+/*  LOOT
+
+    A load order optimisation tool for Oblivion, Skyrim, Fallout 3 and
+    Fallout: New Vegas.
+
+    Copyright (C) 2012-2016    WrinklyNinja
+
+    This file is part of LOOT.
+
+    LOOT is free software: you can redistribute
+    it and/or modify it under the terms of the GNU General Public License
+    as published by the Free Software Foundation, either version 3 of
+    the License, or (at your option) any later version.
+
+    LOOT 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 General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with LOOT.  If not, see
+    <https://www.gnu.org/licenses/>.
+    */
+
+#include "loot/error_categories.h"
+
+namespace loot {
+namespace detail {
+class libloadorder_category : public std::error_category {
+  virtual const char* name() const noexcept {
+    return "libloadorder";
+  }
+
+  virtual std::string message(int ev) const {
+    return "Libloadorder error";
+  }
+
+  virtual bool equivalent(const std::error_code& code, int condition) const noexcept {
+    return code.category().name() == name();
+  }
+};
+}
+
+LOOT_API const std::error_category& libloadorder_category() {
+  static detail::libloadorder_category instance;
+  return instance;
+}
+}

src/backend/game/load_order_handler.cpp

@@ -29,6 +29,7 @@
 #include <boost/log/trivial.hpp>
 
 #include "loot/error.h"
+#include "loot/error_categories.h"
 
 using boost::locale::translate;
 using std::string;
@@ -91,7 +92,7 @@ void LoadOrderHandler::Init(const GameSettings& game, const boost::filesystem::p
       err = translate("libloadorder failed to create a game handle. Details:").str() + " " + e;
     }
     lo_cleanup();
-    throw Error(Error::Code::liblo_error, err);
+    throw std::system_error(ret, libloadorder_category(), err);
   }
 }
 
@@ -112,7 +113,7 @@ bool LoadOrderHandler::IsPluginActive(const std::string& pluginName) const {
       err = translate("libloadorder failed to check if a plugin is active. Details:").str() + " " + e;
     }
     lo_cleanup();
-    throw Error(Error::Code::liblo_error, err);
+    throw std::system_error(ret, libloadorder_category(), err);
   }
 
   return result;
@@ -137,7 +138,7 @@ std::vector<std::string> LoadOrderHandler::GetLoadOrder() const {
       err = translate("libloadorder failed to get the load order. Details:").str() + " " + e;
     }
     lo_cleanup();
-    throw Error(Error::Code::liblo_error, err);
+    throw std::system_error(ret, libloadorder_category(), err);
   }
 
   std::vector<string> loadOrder;
@@ -163,7 +164,7 @@ void LoadOrderHandler::SetLoadOrder(const char * const * const loadOrder, const
       err = translate("libloadorder failed to set the load order. Details:").str() + " " + e;
     }
     lo_cleanup();
-    throw Error(Error::Code::liblo_error, err);
+    throw std::system_error(ret, libloadorder_category(), err);
   }
 }
 

src/tests/backend/game/game_test.h

@@ -98,7 +98,7 @@ TEST_P(GameTest, initShouldThrowOnLinuxIfGamePathIsNotGiven) {
 TEST_P(GameTest, initShouldThrowOnLinuxIfLocalPathIsNotGiven) {
   Game game = Game(GetParam()).SetGamePath(dataPath.parent_path());
   ASSERT_FALSE(boost::filesystem::exists(LootPaths::getLootDataPath() / game.FolderName()));
-  EXPECT_THROW(game.Init(false), Error);
+  EXPECT_THROW(game.Init(false), std::system_error);
 }
 
 // Testing on Windows will find real LOOT installs, and they shouldn't be
@@ -139,7 +139,7 @@ TEST_P(GameTest, redatePluginsShouldThrowIfTheGameHasNotYetBeenInitialisedForSky
   game.SetGamePath(dataPath.parent_path());
 
   if (GetParam() == GameType::tes5)
-    EXPECT_THROW(game.RedatePlugins(), Error);
+    EXPECT_THROW(game.RedatePlugins(), std::system_error);
   else
     EXPECT_NO_THROW(game.RedatePlugins());
 }

src/tests/backend/game/load_order_handler_test.h

@@ -27,7 +27,6 @@ along with LOOT.  If not, see
 
 #include "backend/game/load_order_handler.h"
 
-#include "loot/error.h"
 #include "tests/common_game_test_fixture.h"
 
 namespace loot {
@@ -62,7 +61,7 @@ TEST_P(LoadOrderHandlerTest, initShouldThrowOnLinuxIfNoLocalPathIsSet) {
   GameSettings game(GetParam());
   game.SetGamePath(dataPath.parent_path());
 
-  EXPECT_THROW(loadOrderHandler_.Init(game), Error);
+  EXPECT_THROW(loadOrderHandler_.Init(game), std::system_error);
 }
 #endif
 
@@ -74,7 +73,7 @@ TEST_P(LoadOrderHandlerTest, initShouldNotThrowIfAValidGameIdAndGamePathAndLocal
 }
 
 TEST_P(LoadOrderHandlerTest, isPluginActiveShouldThrowIfTheHandlerHasNotBeenInitialised) {
-  EXPECT_THROW(loadOrderHandler_.IsPluginActive(masterFile), Error);
+  EXPECT_THROW(loadOrderHandler_.IsPluginActive(masterFile), std::system_error);
 }
 
 TEST_P(LoadOrderHandlerTest, isPluginActiveShouldReturnCorrectPluginStatesAfterInitialisation) {
@@ -88,7 +87,7 @@ TEST_P(LoadOrderHandlerTest, isPluginActiveShouldReturnCorrectPluginStatesAfterI
 }
 
 TEST_P(LoadOrderHandlerTest, getLoadOrderShouldThrowIfTheHandlerHasNotBeenInitialised) {
-  EXPECT_THROW(loadOrderHandler_.GetLoadOrder(), Error);
+  EXPECT_THROW(loadOrderHandler_.GetLoadOrder(), std::system_error);
 }
 
 TEST_P(LoadOrderHandlerTest, getLoadOrderShouldReturnTheCurrentLoadOrder) {
@@ -114,7 +113,7 @@ TEST_P(LoadOrderHandlerTest, setLoadOrderShouldThrowIfTheHandlerHasNotBeenInitia
       blankPluginDependentEsp,
   });
 
-  EXPECT_THROW(loadOrderHandler_.SetLoadOrder(loadOrder), Error);
+  EXPECT_THROW(loadOrderHandler_.SetLoadOrder(loadOrder), std::system_error);
 }
 
 TEST_P(LoadOrderHandlerTest, setLoadOrderShouldSetTheLoadOrder) {