fix for #3999 until something better can be done

src/plugins/grass/CMakeLists.txt

@@ -154,10 +154,20 @@ INCLUDE_DIRECTORIES(
 TARGET_LINK_LIBRARIES(grassplugin
   qgisgrass
   qgis_gui
-  grassprovider
   ${OPENPTY_LIBRARY}
 )
 
+# provider must be built as module on OS X so it gets loaded,
+# lookup symbols dynamically instead of linking at compile time
+IF (APPLE)
+    SET_TARGET_PROPERTIES(grassplugin PROPERTIES
+        LINK_FLAGS "-undefined dynamic_lookup")
+ELSE (APPLE)
+    TARGET_LINK_LIBRARIES(grassplugin
+        grassprovider
+    )
+ENDIF (APPLE)
+
 # override default path where built files are put to allow running qgis without installing
 # the binary goes under libexec subdir
 SET (CMAKE_RUNTIME_OUTPUT_DIRECTORY ${QGIS_OUTPUT_DIRECTORY}/${QGIS_LIBEXEC_SUBDIR}/grass/bin)

src/providers/grass/CMakeLists.txt

@@ -47,7 +47,13 @@ ENDIF (APPLE)
 #
 
 QT4_WRAP_CPP(GRASS_PROVIDER_MOC_SRCS qgsgrassprovider.h)
-ADD_LIBRARY(grassprovider SHARED qgsgrassprovider.cpp ${GRASS_PROVIDER_MOC_SRCS})
+# provider must be built as module on OS X so it gets loaded,
+# other modules that need provider symbols must dynamically lookup them
+IF (APPLE)
+    ADD_LIBRARY(grassprovider MODULE qgsgrassprovider.cpp ${GRASS_PROVIDER_MOC_SRCS})
+ELSE (APPLE)
+    ADD_LIBRARY(grassprovider SHARED qgsgrassprovider.cpp ${GRASS_PROVIDER_MOC_SRCS})
+ENDIF (APPLE)
 SET_TARGET_PROPERTIES(grassprovider PROPERTIES COMPILE_FLAGS "\"-DGRASS_EXPORT=${DLLEXPORT}\" \"-DGRASS_LIB_EXPORT=${DLLIMPORT}\"" )
 TARGET_LINK_LIBRARIES(grassprovider qgisgrass)