cmake: Export libcurl and curl targets to use by other cmake projects

The config files define curl and libcurl targets as imported targets
CURL::curl and CURL::libcurl. For backward compatibility with CMake-
provided find-module the CURL_INCLUDE_DIRS and CURL_LIBRARIES are
also set.

Closes #1879

CMake/curl-config.cmake

@@ -0,0 +1,59 @@
+
+get_filename_component(_DIR "${CMAKE_CURRENT_LIST_FILE}" PATH)
+
+if(NOT CURL_FIND_COMPONENTS)
+    set(CURL_FIND_COMPONENTS curl libcurl)
+    if(CURL_FIND_REQUIRED)
+        set(CURL_FIND_REQUIRED_curl TRUE)
+        set(CURL_FIND_REQUIRED_libcurl TRUE)
+    endif()
+endif()
+
+set(_curl_missing_components)
+foreach(_comp ${CURL_FIND_COMPONENTS})
+    if(EXISTS "${_DIR}/${_comp}-target.cmake")
+        include("${_DIR}/${_comp}-target.cmake")
+        set(CURL_${_comp}_FOUND TRUE)
+    else()
+        set(CURL_${_comp}_FOUND FALSE)
+        if(CURL_FIND_REQUIRED_${_comp})
+            set(CURL_FOUND FALSE)
+            list(APPEND _curl_missing_components ${_comp})
+        endif()
+    endif()
+endforeach()
+
+if(_curl_missing_components)
+    set(CURL_NOT_FOUND_MESSAGE "Following required components not found: " ${_curl_missing_components})
+else()
+    if(TARGET CURL::libcurl)
+        string(TOUPPER "${CMAKE_BUILD_TYPE}" _curl_current_config)
+        if(NOT _curl_current_config)
+            set(_curl_current_config "NOCONFIG")
+        endif()
+        get_target_property(_curl_configurations CURL::libcurl IMPORTED_CONFIGURATIONS)
+        list(FIND _curl_configurations "${_curl_current_config}" _i)
+        if(_i LESS 0)
+            set(_curl_config "RELEASE")
+            list(FIND _curl_configurations "${_curl_current_config}" _i)
+            if(_i LESS 0)
+                set(_curl_config "NOCONFIG")
+                list(FIND _curl_configurations "${_curl_current_config}" _i)
+            endif()
+        endif()
+
+        if(_i LESS 0)
+            set(_curl_current_config "") # let CMake pick config at random
+        else()
+	    set(_curl_current_config "_${_curl_current_config}")
+        endif()
+
+        get_target_property(CURL_INCLUDE_DIRS CURL::libcurl INTERFACE_INCLUDE_DIRECTORIES)
+        get_target_property(CURL_LIBRARIES CURL::libcurl "LOCATION${_curl_current_config}")
+        set(_curl_current_config)
+        set(_curl_configurations)
+        set(_i)
+    endif()
+endif()
+
+unset(_curl_missing_components)

CMakeLists.txt

@@ -38,7 +38,7 @@
 # To check:
 # (From Daniel Stenberg) The cmake build selected to run gcc with -fPIC on my box while the plain configure script did not.
 # (From Daniel Stenberg) The gcc command line use neither -g nor any -O options. As a developer, I also treasure our configure scripts's --enable-debug option that sets a long range of "picky" compiler options.
-cmake_minimum_required(VERSION 2.8 FATAL_ERROR)
+cmake_minimum_required(VERSION 2.8.12 FATAL_ERROR)
 set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/CMake;${CMAKE_MODULE_PATH}")
 include(Utilities)
 include(Macros)
@@ -1130,6 +1130,12 @@ function(TRANSFORM_MAKEFILE_INC INPUT_FILE OUTPUT_FILE)
 
 endfunction()
 
+if(WIN32 AND NOT CYGWIN)
+    set(CURL_INSTALL_CMAKE_DIR CMake)
+else()
+    set(CURL_INSTALL_CMAKE_DIR lib/cmake/curl)
+endif()
+
 if(USE_MANUAL)
   add_subdirectory(docs)
 endif()
@@ -1280,6 +1286,25 @@ install(DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/include/curl"
     DESTINATION include
     FILES_MATCHING PATTERN "*.h")
 
+
+include(CMakePackageConfigHelpers)
+write_basic_package_version_file(
+    "${PROJECT_BINARY_DIR}/curl-config-version.cmake"
+    VERSION ${CURL_VERSION}
+    COMPATIBILITY SameMajorVersion
+)
+
+configure_file(CMake/curl-config.cmake
+        "${PROJECT_BINARY_DIR}/curl-config.cmake"
+        COPYONLY
+)
+
+install(
+        FILES ${PROJECT_BINARY_DIR}/curl-config.cmake
+              ${PROJECT_BINARY_DIR}/curl-config-version.cmake
+        DESTINATION ${CURL_INSTALL_CMAKE_DIR}
+)
+
 # Workaround for MSVS10 to avoid the Dialog Hell
 # FIXME: This could be removed with future version of CMake.
 if(MSVC_VERSION EQUAL 1600)

Makefile.am

@@ -30,7 +30,8 @@ CMAKE_DIST = CMakeLists.txt CMake/CMakeConfigurableFile.in      \
  CMake/Macros.cmake              \
  CMake/CurlSymbolHiding.cmake CMake/FindCARES.cmake             \
  CMake/FindLibSSH2.cmake CMake/FindNGHTTP2.cmake                \
- CMake/FindMbedTLS.cmake CMake/cmake_uninstall.cmake.in
+ CMake/FindMbedTLS.cmake CMake/cmake_uninstall.cmake.in         \
+ CMake/curl-config.cmake
 
 VC6_LIBTMPL = projects/Windows/VC6/lib/libcurl.tmpl
 VC6_LIBDSP = projects/Windows/VC6/lib/libcurl.dsp.dist

lib/CMakeLists.txt

@@ -108,7 +108,24 @@ if(WIN32)
   endif()
 endif()
 
+target_include_directories(${LIB_NAME} INTERFACE
+	$<INSTALL_INTERFACE:include>)
+
 install(TARGETS ${LIB_NAME}
+  EXPORT libcurl-target
   ARCHIVE DESTINATION lib
   LIBRARY DESTINATION lib
-  RUNTIME DESTINATION bin)
+  RUNTIME DESTINATION bin
+)
+
+export(TARGETS ${LIB_NAME}
+       APPEND FILE ${PROJECT_BINARY_DIR}/libcurl-target.cmake
+       NAMESPACE CURL::
+)
+
+install(EXPORT libcurl-target
+        FILE libcurl-target.cmake
+        NAMESPACE CURL::
+        DESTINATION ${CURL_INSTALL_CMAKE_DIR}
+)
+

src/CMakeLists.txt

@@ -76,4 +76,15 @@ set_target_properties(${EXE_NAME} PROPERTIES
 
 #INCLUDE(ModuleInstall OPTIONAL)
 
-install(TARGETS ${EXE_NAME} DESTINATION bin)
+install(TARGETS ${EXE_NAME} EXPORT curl-target DESTINATION bin)
+export(TARGETS ${EXE_NAME}
+       APPEND FILE ${PROJECT_BINARY_DIR}/curl-target.cmake
+       NAMESPACE CURL::
+)
+
+install(EXPORT curl-target
+        FILE curl-target.cmake
+        NAMESPACE CURL::
+        DESTINATION ${CURL_INSTALL_CMAKE_DIR}
+)
+