Cmake "No rule to make target" while building shared library - build

Question

Im trying to build a vala-application together with an own library in the same project using CMake. Building the application works fine, so I've added a new "lib" directory to my project with the following CMakeLists.txt:
# Configure precompile
vala_precompile (LIB_VALA_C ${LIB_NAME}
Session.vala
PACKAGES
gio-2.0
gee-0.8
OPTIONS
--thread
--vapidir=${CMAKE_SOURCE_DIR}/vapi
--target-glib 2.32
GENERATE_VAPI
${LIB_NAME}
GENERATE_HEADER
${CMAKE_PROJECT_NAME}
)
# Add executable
add_library (${LIB_NAME} SHARED ${LIB_VALA_C})
# Set library properties
set_target_properties (${LIB_NAME} PROPERTIES
OUTPUT_NAME ${LIB_NAME}
VERSION ${LIB_SOVERSION}.${LIB_VERSION}
SOVERSION ${LIB_SOVERSION}
)
target_link_libraries (${LIB_NAME} ${LIB_LIBRARIES})
# Installation
install (TARGETS ${LIB_NAME} DESTINATION ${CMAKE_INSTALL_FULL_LIBDIR}/)
install (FILES ${CMAKE_CURRENT_BINARY_DIR}/${LIB_NAME}.pc DESTINATION ${CMAKE_INSTALL_FULL_LIBDIR}/pkgconfig/)
install (FILES ${CMAKE_CURRENT_BINARY_DIR}/${LIB_NAME}.vapi DESTINATION ${CMAKE_INSTALL_FULL_DATAROOTDIR}/vala/vapi/)
install (FILES ${CMAKE_CURRENT_SOURCE_DIR}/${LIB_NAME}.deps DESTINATION ${CMAKE_INSTALL_FULL_DATAROOTDIR}/vala/vapi/)
install (FILES ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_PROJECT_NAME}.h DESTINATION ${CMAKE_INSTALL_FULL_INCLUDEDIR}/${LIB_NAME}/)
The CMakeLists.txt in the project's root contains the following:
# Project name
project (drop)
# Minimum requirements of build-system
cmake_minimum_required (VERSION 2.8)
cmake_policy (VERSION 2.6)
# Global configuration
set (DATADIR "${CMAKE_INSTALL_PREFIX}/share")
set (PKGDATADIR "${DATADIR}/${CMAKE_PROJECT_NAME}")
set (GETTEXT_PACKAGE "${CMAKE_PROJECT_NAME}")
set (RELEASE_NAME "${CMAKE_PROJECT_NAME}")
set (VERSION "0.1")
set (VERSION_INFO "Release")
set (PREFIX ${CMAKE_INSTALL_PREFIX})
set (DOLLAR "$")
# Library configuration
set (LIB_VERSION 1.0)
set (LIB_SOVERSION 0)
set (LIB_NAME ${CMAKE_PROJECT_NAME}-${LIB_VERSION})
# Cmake-files
list (APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/cmake)
# Configuration file
configure_file (${CMAKE_SOURCE_DIR}/dropd/config.vala.cmake ${CMAKE_SOURCE_DIR}/dropd/config.vala)
# Check for vala
find_package (Vala REQUIRED)
include (ValaVersion)
ensure_vala_version ("0.18" MINIMUM)
include (ValaPrecompile)
# Disable C compiler warnings
add_definitions (-w)
# Set gettext-package
add_definitions (-DGETTEXT_PACKAGE="${CMAKE_PROJECT_NAME}")
# Check for required dependencies
find_package (PkgConfig)
pkg_check_modules (DEPS REQUIRED granite gthread-2.0 gio-2.0 gee-0.8 avahi-gobject avahi-client)
# Link the avahi library
add_definitions (-lavahi)
# Link dependencies
add_definitions (${DEPS_CFLAGS})
add_definitions (${LIB_CFLAGS})
link_libraries (${DEPS_LIBRARIES})
link_directories (${DEPS_LIBRARY_DIRS})
link_directories (${LIB_LIBRARY_DIRS})
# Load directories
add_subdirectory (dropd)
add_subdirectory (lib)
add_subdirectory (po)
add_subdirectory (data)
add_subdirectory (schemas)
When building the project now the main application still builds without problems, but when the build of the library begins this error appears (translated):
make[2]: *** No rule to make »../lib/drop-1.0«,
required by »lib/drop-1.0«. End.
make[1]: *** [lib/CMakeFiles/drop-1.0.dir/all] Errors 2
make: *** [all] Errors 2
Badly Im not that familar with CMake and don't get what that error message means, neither what is causing it.
I have already compared my CMakeLists.txt files with them in another project that's also built out of a 'normal' application and one library, but I couldn't find the difference that makes my code not working: http://bazaar.launchpad.net/~wingpanel-devs/wingpanel/trunk/files/head:/
It would be very nice if you could give me some tips what I could have missed in the CMake-Files.

Answer 1

For the ones with the same problem: I've now solved the issue myself with removing the ${LIB_NAME} from the line vala_precompile (LIB_VALA_C ${LIB_NAME}. Im still not sure what's happening here, but this "solution" seemed to work.
Better ways to solve this issue are still appreciated. ;)