Allow unloading plugins that use std::regex

library/CMakeLists.txt

@@ -57,6 +57,7 @@ include/wdirent.h
 SET(MAIN_SOURCES
 Core.cpp
 ColorText.cpp
+CompilerWorkAround.cpp
 DataDefs.cpp
 Debug.cpp
 Error.cpp

library/CompilerWorkAround.cpp

@@ -0,0 +1,32 @@
+#include <regex>
+
+namespace DFHack {
+namespace neverCalled {
+
+/**
+ * gcc/linstdc++ seems to generate code that links libstdc++ back to first
+ * shared object using std::regex. To allow plugins unload with std::regex in
+ * the code we need the std::regex functions inside libdfhack.so.
+ *
+ * If your plugin decides to use any overloads that aren't listed here it may
+ * stay in memory after dlclose.
+ */
+std::regex stdRegexPluginUnloadWorkaround()
+{
+    std::regex fake("foo");
+    std::string haystack("bar is foo in the world");
+    std::regex fake2(std::string("bar"));
+    if (std::regex_match(haystack, fake))
+        std::swap(fake, fake2);
+    if (std::regex_search(haystack, fake))
+        std::swap(fake, fake2);
+    const char* haystack2 = "foo";
+    if (std::regex_match(haystack2, fake))
+        std::swap(fake, fake2);
+    if (std::regex_search(haystack2, fake))
+        std::swap(fake, fake2);
+    return fake;
+}
+
+}
+}