Detect libstdc++ ABI incompatibility to allow compiling using clang again.

Currently, this is only relevant when using LevelDB, and a newer version
of libstdc++, which uses a different C++ ABI which clang does not yet support.

A symptom of the problem are unexpected linking failures, caused by undefined
symbols, while other symbols from the same library do not cause errors.

The solution is a workaround, that avoids using the offending symbols, at the
cost of reduced functionality. As this currently only affects the text of an
error message, the impact is minor.

CMakeLists.txt

@@ -250,6 +250,24 @@ if(NOT USE_SQLITE3 AND NOT USE_POSTGRESQL AND NOT USE_LEVELDB AND NOT USE_REDIS)
 	message(SEND_ERROR "No database backends are configured, or none could be found")
 endif(NOT USE_SQLITE3 AND NOT USE_POSTGRESQL AND NOT USE_LEVELDB AND NOT USE_REDIS)
 
+# Determine whether there is a libstdc++ ABI incompatibility.
+# Currently only needed for leveldb.
+set(CPP_ABI_STDSTRING_OK 1)
+if(USE_LEVELDB)
+	# try_compile does not remove the temporary build directory, so put it in CMakeFiles...
+	# Also: use absolute paths; cmake chokes on relative paths :-(
+	# AARGH! try_compile does not understand the INCLUDE_DIRECTORIES directive.
+	try_compile(CPP_ABI_STDSTRING_RESULT
+			"${CMAKE_HOME_DIRECTORY}/CMakeFiles/CMakeTmp/abi-stdstring-test"
+			"${CMAKE_HOME_DIRECTORY}/cmake/abi-stdstring.cpp"
+			LINK_LIBRARIES ${LEVELDB_LIBRARY})
+			#INCLUDE_DIRECTORIES ${LEVELDB_INCLUDE_DIR}
+	if(NOT CPP_ABI_STDSTRING_RESULT)
+		set(CPP_ABI_STDSTRING_OK 0)
+		message(STATUS "C++ library ABI mismatch for std::string. Enabling workaround - this may affect functionality")
+	endif(NOT CPP_ABI_STDSTRING_RESULT)
+endif(USE_LEVELDB)
+
 include_directories(
 	"${PROJECT_BINARY_DIR}"
 	"${CMAKE_CURRENT_SOURCE_DIR}"

Changelog

@@ -11,6 +11,8 @@
 	- Fixed failure to compile with gcc 6
 	- Fixed failure to compile when rpm is not installed
 		(e.g. on non-rpm systems...)
+	- Workaround to allow compilation with clang when using leveldb.
+		This is broken due to libstdc++ ABI incompatibility
 [31 May 2016]
     Features:
 	- Support for postgresql backend added

MSVC/gen-build-config.bat

@@ -285,6 +285,7 @@ EXIT /B %$EXITVAL%
 	SET $LINE=!$LINE:@VERSION_MINOR@=%$VERSION_MINOR%!
 	SET $LINE=!$LINE:@PACKAGING_FLAT@=%$PACKAGING_FLAT%!
 	SET $LINE=!$LINE:@INSTALL_PREFIX@=%$INSTALL_PREFIX%!
+	SET $LINE=!$LINE:@CPP_ABI_STDSTRING_OK@=1!
 	
 	ECHO %$INDENT%%$LINE% >> %$OUTPUT%
 	ENDLOCAL

build_config.h.in

@@ -21,5 +21,7 @@
 #define PACKAGING_FLAT @PACKAGING_FLAT@
 #define INSTALL_PREFIX "@INSTALL_PREFIX@"
 
+#define CPP_ABI_STDSTRING_OK @CPP_ABI_STDSTRING_OK@
+
 #endif
 

cmake/abi-stdstring.cpp

@@ -0,0 +1,7 @@
+#include <string>
+#include <leveldb/status.h>
+int main(void) {
+	leveldb::Status status;
+	std::string str = status.ToString();
+	return 0;
+}

db-leveldb.cpp

@@ -1,6 +1,7 @@
 #include "db-leveldb.h"
 #include <stdexcept>
 #include <sstream>
+#include "build_config.h"
 #include "types.h"
 
 inline int64_t stoi64(const std::string &s) {
@@ -26,7 +27,16 @@ DBLevelDB::DBLevelDB(const std::string &mapdir) :
 	options.create_if_missing = false;
 	leveldb::Status status = leveldb::DB::Open(options, mapdir + "map.db", &m_db);
 	if(!status.ok())
+		#if CPP_ABI_STDSTRING_OK
 		throw std::runtime_error(std::string("Failed to open Database: ") + status.ToString());
+		#else
+		throw std::runtime_error(std::string("Failed to open Database: ") +
+			( status.ok() ? "Ok (??? how is this possible ???"")"		// "" is needed to prevent interpretation as trigraph -shudder-
+			: status.IsNotFound() ? "NotFound"
+			: status.IsCorruption() ? "Corruption"
+			: status.IsIOError() ? "IOError"
+			: "Cannot determine error type - could be NotSupported or InvalidArgument or something else"));
+		#endif
 }
 
 DBLevelDB::~DBLevelDB() {