CMake: Restore order-dependent library checks

Revert commit 2257deb502 (Cmake: Avoid cycle directory dependencies,
2014-08-22) and add a comment explaining the purpose of the original
code.

The check_library_exists_concat macro is intended to be called multiple
times on a sequence of possibly dependent libraries.  Later libraries
may depend on earlier libraries when they are static.  They cannot be
safely linked in reverse order on some platforms.

Signed-off-by: Brad King <brad.king@kitware.com>

diff --git a/CMake/Macros.cmake b/CMake/Macros.cmake
index 9b9338e523cc4eba62477675b134643f07c09e2a..df15b7406bb9ff6659843f182711d12b48012ace 100644 (file)
--- a/CMake/Macros.cmake
+++ b/CMake/Macros.cmake
@@ -1,12 +1,15 @@
 #File defines convenience macros for available feature testing
 
 # This macro checks if the symbol exists in the library and if it
-# does, it appends library to the list.
+# does, it prepends library to the list.  It is intended to be called
+# multiple times with a sequence of possibly dependent libraries in
+# order of least-to-most-dependent.  Some libraries depend on others
+# to link correctly.
 macro(CHECK_LIBRARY_EXISTS_CONCAT LIBRARY SYMBOL VARIABLE)
-  check_library_exists("${CURL_LIBS};${LIBRARY}" ${SYMBOL} "${CMAKE_LIBRARY_PATH}"
+  check_library_exists("${LIBRARY};${CURL_LIBS}" ${SYMBOL} "${CMAKE_LIBRARY_PATH}"
     ${VARIABLE})
   if(${VARIABLE})
-    list(APPEND CURL_LIBS ${LIBRARY})
+    set(CURL_LIBS ${LIBRARY} ${CURL_LIBS})
   endif(${VARIABLE})
 endmacro(CHECK_LIBRARY_EXISTS_CONCAT)