CMake FIND_LIBRARY returns wrong path - cmake

Question

In my project I use differend 3rd libraries, which has been prebuild and added to external-debs subdirectory. I use multiple FindXXX CMake scripts to locate those requirements.
When I try to locate a FreeImage prebuild, CMake find the library successfully but returns always the wrong path lib/libfreeimage.a instead of ./external-debs/freeimage/lib/windows/x64/libfreeimage.a
This is my search operation:
FIND_LIBRARY(FREE_IMAGE_LIBRARY
NAMES ${LIB_PREFIX}freeimage.${LIB_POSTFIX}
HINTS ${FREE_IMAGE_LIBRARY_DIR}
)
And this are my predefintions:
# Determine platform architecture
IF (CMAKE_SIZEOF_VOID_P EQUAL 8 )
SET(ARCHITECTURE "x64")
ELSE()
SET(ARCHITECTURE "x86")
ENDIF()
#Determine platform specific include and library
#paths settings.
IF (WIN32)
IF (MINGW)
SET (LIB_PREFIX "lib")
SET (LIB_POSTFIX "a")
ELSEIF (MSVC)
SET (LIB_POSTFIX "lib")
ENDIF(MINGW)
SET (PLATFORM "windows")
ELSE (UNIX)
SET (LIB_PREFIX "lib")
SET (LIB_POSTFIX "a")
SET (PLATFORM "linux")
ENDIF (WIN32)
SET(FREE_IMAGE_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/external-deps/freeimage/include)
SET(FREE_IMAGE_LIBRARY_DIR ${CMAKE_SOURCE_DIR}/external-deps/freeimage/lib/${PLATFORM}/${ARCHITECTURE})
I use this same code to locate an other pre-build 3rd libary dependency (jsoncpp) located in same external-deps subfolder without any issue.
Execute: FindJSON.cmake
-- [INFO]: Find JSON include: ./external-deps/jsoncpp/include
-- [INFO]: Find JSON lib: ./external-deps/jsoncpp/lib/windows/x64/libjsoncpp.a
Execute: FindFreeImage.cmake
-- [INFO]: Find FreeImage include: ./external-deps/freeimage/include
-- [INFO]: Find FreeImage lib: /lib/libfreeimage.a
I'am using CMake 2.8.x on windows platform.
Has anyone an idea why CMake sometimes return a wrong library path?

Answer 1

It looks like CMake has found another installation of the library in your MinGW environment. This might be a false positive.
Use NO_DEFAULT_PATH if you want to force CMake to use a library from a specific directory:
FIND_LIBRARY(FREE_IMAGE_LIBRARY
NAMES ${LIB_PREFIX}freeimage.${LIB_POSTFIX}
HINTS ${FREE_IMAGE_LIBRARY_DIR}
NO_DEFAULT_PATH
)
Take a look at the CMake command reference to get some insight on the subtle rules that drive the path resolution in find_library.

Answer 2

One thing to remember about find_library() is that CMake does not do the search if it thinks it already knows where the library is. Removing CMake's cache (build directory) can often help.