Add FILESYSTEM_openDirectory() and _openDirectoryEnabled()

Have to add some includes and put these behind some ifdefs, of course.

I'm pretty sure FreeBSD and OpenBSD and Haiku are POSIX enough that the
"open" command will work on them, too.

I would've loved to make FILESYSTEM_openDirectoryEnabled a simple bool
instead of a function, but I ran into issues with putting it in the
FileSystemUtils header file, so I'll just make it a function and call it
a day.

desktop_version/src/FileSystemUtils.cpp

@@ -19,6 +19,7 @@
 #if defined(_WIN32)
 #include <windows.h>
 #include <shlobj.h>
+#include <shellapi.h>
 int mkdir(char* path, int mode)
 {
 	WCHAR utf16_path[MAX_PATH];
@@ -33,6 +34,9 @@ int mkdir(char* path, int mode)
 /* These are needed for PLATFORM_* crap */
 #include <unistd.h>
 #include <dirent.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <spawn.h>
 #define MAX_PATH PATH_MAX
 #endif
 
@@ -465,3 +469,49 @@ void PLATFORM_copyFile(const char *oldLocation, const char *newLocation)
 	/* WTF did we just do */
 	printf("Copied:\n\tOld: %s\n\tNew: %s\n", oldLocation, newLocation);
 }
+
+#ifdef _WIN32
+bool FILESYSTEM_openDirectoryEnabled()
+{
+	return true;
+}
+
+bool FILESYSTEM_openDirectory(const char *dname)
+{
+	ShellExecute(NULL, "open", dname, NULL, NULL, SW_SHOWMINIMIZED);
+	return true;
+}
+#elif defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__HAIKU__)
+bool FILESYSTEM_openDirectoryEnabled()
+{
+	return true;
+}
+ #ifdef __linux__
+const char* open_cmd = "xdg-open";
+ #else
+const char* open_cmd = "open";
+ #endif
+
+extern "C" char** environ;
+
+bool FILESYSTEM_openDirectory(const char *dname)
+{
+	pid_t child;
+	// This const_cast is legal (ctrl-f "The statement" at https://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html
+	char* argv[3] = {const_cast<char*>(open_cmd), const_cast<char*>(dname), NULL};
+	posix_spawnp(&child, open_cmd, NULL, NULL, argv, environ);
+	int status = 0;
+	waitpid(child, &status, 0);
+	return WIFEXITED(status) && WEXITSTATUS(status) == 0;
+}
+#else
+bool FILESYSTEM_openDirectoryEnabled()
+{
+	return false;
+}
+
+bool FILESYSTEM_openDirectory(const char *dname)
+{
+	return false;
+}
+#endif

desktop_version/src/FileSystemUtils.h

@@ -20,4 +20,7 @@ bool FILESYSTEM_loadTiXmlDocument(const char *name, TiXmlDocument *doc);
 
 std::vector<std::string> FILESYSTEM_getLevelDirFileNames();
 
+bool FILESYSTEM_openDirectoryEnabled();
+bool FILESYSTEM_openDirectory(const char *dname);
+
 #endif /* FILESYSTEMUTILS_H */