A bunch of CMake fixes (#114)

CMakeLists.txt

@@ -1,28 +1,8 @@
-cmake_minimum_required(VERSION 3.9)
+cmake_minimum_required(VERSION 3.9...3.31)
 project(aws-c-iot C)
 
 option(USE_EXTERNAL_DEPS_SOURCES "Use dependencies provided by add_subdirectory command" OFF)
 
-if (DEFINED CMAKE_PREFIX_PATH)
-    file(TO_CMAKE_PATH "${CMAKE_PREFIX_PATH}" CMAKE_PREFIX_PATH)
-endif()
-
-if (DEFINED CMAKE_INSTALL_PREFIX)
-    file(TO_CMAKE_PATH "${CMAKE_INSTALL_PREFIX}" CMAKE_INSTALL_PREFIX)
-endif()
-
-if (UNIX AND NOT APPLE)
-    include(GNUInstallDirs)
-elseif(NOT DEFINED CMAKE_INSTALL_LIBDIR)
-    set(CMAKE_INSTALL_LIBDIR "lib")
-endif()
-
-# This is required in order to append /lib/cmake to each element in CMAKE_PREFIX_PATH
-set(AWS_MODULE_DIR "/${CMAKE_INSTALL_LIBDIR}/cmake")
-string(REPLACE ";" "${AWS_MODULE_DIR};" AWS_MODULE_PATH "${CMAKE_PREFIX_PATH}${AWS_MODULE_DIR}")
-# Append that generated list to the module search path
-list(APPEND CMAKE_MODULE_PATH ${AWS_MODULE_PATH})
-
 if (USE_EXTERNAL_DEPS_SOURCES)
     set(IN_SOURCE_BUILD ON)
 
@@ -35,12 +15,18 @@ if (USE_EXTERNAL_DEPS_SOURCES)
     list(APPEND CMAKE_MODULE_PATH "${aws-c-common_SOURCE_DIR}/cmake")
 endif()
 
+if (NOT IN_SOURCE_BUILD)
+    # this is required so we can use aws-c-common's CMake modules
+    find_package(aws-c-common REQUIRED)
+endif()
+
 include(AwsCFlags)
 include(AwsCheckHeaders)
 include(AwsSharedLibSetup)
 include(AwsSanitizers)
 include(CheckCCompilerFlag)
 include(AwsFindPackage)
+include(GNUInstallDirs)
 
 # Platform specific includes and source
 
@@ -108,8 +94,8 @@ aws_use_package(aws-c-mqtt)
 target_link_libraries(${PROJECT_NAME} PUBLIC ${DEP_AWS_LIBS})
 aws_prepare_shared_lib_exports(${PROJECT_NAME})
 
-install(FILES ${AWS_IOT_HEADERS}  DESTINATION "include/aws/iotdevice" COMPONENT Development)
-install(FILES ${AWS_IOT_PRIV_EXPOSED_HEADERS}  DESTINATION "include/aws/iotdevice/private" COMPONENT Development)
+install(FILES ${AWS_IOT_HEADERS}  DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/aws/iotdevice" COMPONENT Development)
+install(FILES ${AWS_IOT_PRIV_EXPOSED_HEADERS}  DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/aws/iotdevice/private" COMPONENT Development)
 
 if (BUILD_SHARED_LIBS)
    set (TARGET_DIR "shared")
@@ -118,7 +104,7 @@ else()
 endif()
 
 install(EXPORT "${PROJECT_NAME}-targets"
-        DESTINATION "${LIBRARY_DIRECTORY}/${PROJECT_NAME}/cmake/${TARGET_DIR}"
+        DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}/${TARGET_DIR}"
         NAMESPACE AWS::
         COMPONENT Development)
 
@@ -127,7 +113,7 @@ configure_file("cmake/${PROJECT_NAME}-config.cmake"
         @ONLY)
 
 install(FILES "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}-config.cmake"
-        DESTINATION "${LIBRARY_DIRECTORY}/${PROJECT_NAME}/cmake/"
+        DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}/"
         COMPONENT Development)
 
 include(CTest)