Case sensitive file paths on Windows

The intent is to avoid UMC authors accidentally mistyping a file name
and making an addon that doesn't work correctly on GNU/Linux.

Thanks to @Arcanister for suggesting the GetFinalPathNameByHandle function.

changelog

@@ -1,4 +1,6 @@
 Version 1.13.11:
+ * WML Engine:
+   * File paths are now case sensitive even on Windows.
 
 Version 1.13.10:
  * Add-ons client:

src/filesystem.hpp

@@ -54,6 +54,9 @@ enum file_name_option { ENTIRE_FILE_PATH, FILE_NAME_ONLY };
 enum file_filter_option { NO_FILTER, SKIP_MEDIA_DIR, SKIP_PBL_FILES };
 enum file_reorder_option { DONT_REORDER, DO_REORDER };
 
+/** Some tasks to run on startup. */
+void init();
+
 /**
  * Populates 'files' with all the files and
  * 'dirs' with all the directories in dir.

src/filesystem_boost.cpp

@@ -43,6 +43,7 @@ using boost::uintmax_t;
 #include "config.hpp"
 #include "game_config.hpp"
 #include "log.hpp"
+#include "serialization/unicode_cast.hpp"
 #include "version.hpp"
 
 static lg::log_domain log_filesystem("filesystem");
@@ -189,12 +190,42 @@ namespace {
 	};
 
 	static static_runner static_bfs_path_imbuer;
+
+	typedef DWORD(WINAPI *GetFinalPathNameByHandleWPtr)(HANDLE, LPWSTR, DWORD, DWORD);
+	static GetFinalPathNameByHandleWPtr dyn_GetFinalPathNameByHandle;
 #endif
+
+	bool is_filename_case_correct(const std::string& fname, const boost::iostreams::file_descriptor_source& fd)
+	{
+#ifdef _WIN32
+		if(dyn_GetFinalPathNameByHandle == nullptr) {
+			// Windows XP. Just assume that the case is correct.
+			return true;
+		}
+
+		wchar_t real_path[MAX_PATH];
+		dyn_GetFinalPathNameByHandle(fd.handle(), real_path, MAX_PATH - 1, VOLUME_NAME_NONE);
+		std::string real_name = filesystem::base_name(unicode_cast<std::string>(std::wstring(real_path)));
+		return real_name == filesystem::base_name(fname);
+#else
+		return true;
+#endif
+	}
 }
 
 
 namespace filesystem {
 
+void init()
+{
+#ifdef _WIN32
+	HMODULE kernel32 = GetModuleHandle(TEXT("Kernel32.dll"));
+	// Note that this returns a null pointer on Windows XP!
+	dyn_GetFinalPathNameByHandle = reinterpret_cast<GetFinalPathNameByHandleWPtr>(
+		GetProcAddress(kernel32, "GetFinalPathNameByHandleW"));
+#endif
+}
+
 static void push_if_exists(std::vector<std::string> *vec, const path &file, bool full) {
 	if (vec != nullptr) {
 		if (full)
@@ -779,6 +810,11 @@ filesystem::scoped_istream istream_file(const std::string &fname, bool treat_fai
 		//TODO: has this still use ?
 		if (!fd.is_open() && treat_failure_as_error) {
 			ERR_FS << "Could not open '" << fname << "' for reading.\n";
+		} else if (!is_filename_case_correct(fname, fd)) {
+			ERR_FS << "Not opening '" << fname << "' due to case mismatch.\n";
+			filesystem::scoped_istream s(new bfs::ifstream());
+			s->clear(std::ios_base::failbit);
+			return s;
 		}
 		return filesystem::scoped_istream(new boost::iostreams::stream<boost::iostreams::file_descriptor_source>(fd, 4096, 0));
 	}

src/wesnoth.cpp

@@ -1003,6 +1003,8 @@ int main(int argc, char** argv)
 #endif
 #endif //_OPENMP
 
+	filesystem::init();
+
 	if(SDL_Init(SDL_INIT_TIMER) < 0) {
 		fprintf(stderr, "Couldn't initialize SDL: %s\n", SDL_GetError());
 		return(1);