CMake: check if the compiler supports using precompiled headers

Build the cotire test project and check if it succeeds. Also check if the
'had text segment at different address' warning does not appear in the build
output. If it does not succeed, disable usage of precompiled headers.

If the PCH option was changed, clean the project and rebuild it again. Do not
clean everytime the project is configured because (re)building the cotire test
project takes some time.

build/cmake/init.cmake

@@ -530,3 +530,37 @@ if(wxUSE_GUI)
         set(wxUSE_LIBGNOMEVFS OFF)
     endif()
 endif()
+
+# test if precompiled headers are supported using the cotire test project
+if(DEFINED wxBUILD_PRECOMP_PREV AND NOT wxBUILD_PRECOMP STREQUAL wxBUILD_PRECOMP_PREV)
+    set(CLEAN_PRECOMP_TEST TRUE)
+endif()
+set(wxBUILD_PRECOMP_PREV ${wxBUILD_PRECOMP} CACHE INTERNAL "")
+
+if(wxBUILD_PRECOMP)
+    if (CLEAN_PRECOMP_TEST)
+        try_compile(RESULT_VAR_CLEAN
+                    "${wxBINARY_DIR}/CMakeFiles/cotire_test"
+                    "${wxSOURCE_DIR}/build/cmake/modules/cotire_test"
+                    CotireExample clean_cotire
+        )
+    endif()
+    try_compile(RESULT_VAR
+                "${wxBINARY_DIR}/CMakeFiles/cotire_test"
+                "${wxSOURCE_DIR}/build/cmake/modules/cotire_test"
+                CotireExample OUTPUT_VARIABLE OUTPUT_VAR
+    )
+
+    # check if output has precompiled header warnings. The build can still succeed, so check the output
+    # likely caused by gcc hardening: https://bugzilla.redhat.com/show_bug.cgi?id=1721553
+    # cc1plus: warning /path/to/project/cotire/name_CXX_prefix.hxx.gch: had text segment at different address
+    string(FIND "${OUTPUT_VAR}" "had text segment at different address" HAS_MESSAGE)
+    if(${HAS_MESSAGE} GREATER -1)
+        set(RESULT_VAR FALSE)
+    endif()
+
+    if(NOT RESULT_VAR)
+        message(WARNING "precompiled header (PCH) test failed, it will be turned off")
+        wx_option_force_value(wxBUILD_PRECOMP OFF)
+    endif()
+endif(wxBUILD_PRECOMP)

build/cmake/modules/cotire_test/CMakeLists.txt

@@ -0,0 +1,21 @@
+# cotire example project
+
+cmake_minimum_required(VERSION 2.8.12)
+
+if (POLICY CMP0058)
+	# Ninja requires custom command byproducts to be explicit
+	cmake_policy(SET CMP0058 NEW)
+endif()
+
+project (CotireExample)
+
+set (CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/..")
+
+if (NOT CMAKE_VERSION VERSION_LESS "3.1.0")
+	set (CMAKE_CXX_STANDARD "98")
+	set (CMAKE_CXX_EXTENSIONS OFF)
+endif()
+
+include(cotire)
+
+add_subdirectory(src)

build/cmake/modules/cotire_test/license

@@ -0,0 +1,22 @@
+Copyright (c) 2012-2018 Sascha Kratky
+
+Permission is hereby granted, free of charge, to any person
+obtaining a copy of this software and associated documentation
+files (the "Software"), to deal in the Software without
+restriction, including without limitation the rights to use,
+copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.

build/cmake/modules/cotire_test/src/CMakeLists.txt

@@ -0,0 +1,31 @@
+# cotire example project
+
+add_executable(example main.cpp example.cpp log.cpp log.h example.h)
+
+# enable warnings
+if (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+	set_target_properties(example PROPERTIES COMPILE_FLAGS "-Weverything")
+elseif (CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+	set_target_properties(example PROPERTIES COMPILE_FLAGS "-Wall -Wextra")
+endif()
+
+cotire(example)
+
+# cotire sets the following properties
+get_target_property(_unitySource example COTIRE_CXX_UNITY_SOURCE)
+get_target_property(_prefixHeader example COTIRE_CXX_PREFIX_HEADER)
+get_target_property(_precompiledHeader example COTIRE_CXX_PRECOMPILED_HEADER)
+get_target_property(_unityTargetName example COTIRE_UNITY_TARGET_NAME)
+
+if (_unitySource)
+	message(STATUS "example unity source: ${_unitySource}")
+endif()
+if (_prefixHeader)
+	message(STATUS "example prefix header: ${_prefixHeader}")
+endif()
+if (_precompiledHeader)
+	message(STATUS "example precompiled header: ${_precompiledHeader}")
+endif()
+if (TARGET ${_unityTargetName})
+	message(STATUS "example unity target: ${_unityTargetName}")
+endif()

build/cmake/modules/cotire_test/src/example.cpp

@@ -0,0 +1,24 @@
+// cotire example project
+
+#include "example.h"
+
+#ifndef NDEBUG
+#include <algorithm>
+#include <iterator>
+#endif
+
+namespace example {
+
+std::string get_message() {
+	char msg_chrs[] = { 'C', 'o', 't', 'i', 'r', 'e', 'd', '!' };
+#ifdef NDEBUG
+	return std::string(&msg_chrs[0], &msg_chrs[sizeof(msg_chrs)]);
+#else
+	std::string msg;
+	msg.reserve(sizeof(msg_chrs));
+	std::copy(msg_chrs, msg_chrs + sizeof(msg_chrs), std::back_inserter(msg));
+	return msg;
+#endif
+}
+
+}

build/cmake/modules/cotire_test/src/example.h

@@ -0,0 +1,10 @@
+// cotire example project
+
+#include <string>
+
+namespace example {
+
+std::string get_message();
+
+}
+

build/cmake/modules/cotire_test/src/log.cpp

@@ -0,0 +1,17 @@
+// cotire example project
+
+#include "log.h"
+
+#include <iostream>
+
+namespace logging {
+
+void error(const std::string& msg) {
+	std::cerr << msg << std::endl;
+}
+
+void info(const std::string& msg) {
+	std::cout << msg << std::endl;
+}
+
+}

build/cmake/modules/cotire_test/src/log.h

@@ -0,0 +1,10 @@
+// cotire example project
+
+#include <string>
+
+namespace logging {
+
+void error(const std::string& msg);
+void info(const std::string& msg);
+
+}

build/cmake/modules/cotire_test/src/main.cpp

@@ -0,0 +1,12 @@
+// cotire example project main
+
+#include <string>
+
+#include "example.h"
+#include "log.h"
+
+int main()
+{
+	std::string msg = example::get_message();
+	logging::info(msg);
+}