cmake exported targets

The minimum required cmake version is raised to 3.1,
because the exported targets started at that version.

The build system creates the exported targets:
- The executable uchardet::uchardet
- The library uchardet::libuchardet
- The static library uchardet::libuchardet_static

A downstream project using CMake can find and link the library target
directly with cmake (without needing pkg-config) this way:

~~~
project(sample LANGUAGES C)
find_package ( uchardet )
if (uchardet_FOUND)
  add_executable( sample sample.c )
  target_link_libraries ( sample PRIVATE uchardet::libuchardet )
endif ()
~~~

After installing uchardet in a prefix like "$HOME/uchardet/":
cmake -DCMAKE_PREFIX_PATH="$HOME/uchardet/;..."

Instead installing, the build directory can be used directly, for
instance:

cmake -Duchardet_DIR="$HOME/uchardet-0.1.0/build/" ...

CMakeLists.txt

@@ -1,5 +1,5 @@
 ######## Project settings
-cmake_minimum_required(VERSION 2.8.5)
+cmake_minimum_required(VERSION 3.1)
 include(CheckCCompilerFlag)
 set (PACKAGE_NAME uchardet)
 project (${PACKAGE_NAME} CXX C)
@@ -72,3 +72,39 @@ install(
 add_subdirectory(src)
 add_subdirectory(doc)
 add_subdirectory(test)
+
+######## Exported targets
+
+install(
+	EXPORT UchardetTargets
+	FILE ${PACKAGE_NAME}-targets.cmake
+	NAMESPACE ${PACKAGE_NAME}::
+	DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${PACKAGE_NAME}
+)
+
+export(
+	EXPORT UchardetTargets
+	FILE "${CMAKE_CURRENT_BINARY_DIR}/${PACKAGE_NAME}-targets.cmake"
+	NAMESPACE ${PACKAGE_NAME}::
+)
+
+include(CMakePackageConfigHelpers)
+write_basic_package_version_file(
+	${PACKAGE_NAME}-config-version.cmake
+	VERSION ${UCHARDET_VERSION}
+	COMPATIBILITY AnyNewerVersion
+)
+
+configure_file(
+	${PACKAGE_NAME}-config.cmake.in
+	${PACKAGE_NAME}-config.cmake
+	@ONLY
+)
+
+install (
+	FILES
+		"${CMAKE_CURRENT_BINARY_DIR}/${PACKAGE_NAME}-config.cmake"
+		"${CMAKE_CURRENT_BINARY_DIR}/${PACKAGE_NAME}-config-version.cmake"
+	DESTINATION
+		${CMAKE_INSTALL_LIBDIR}/cmake/${PACKAGE_NAME}
+)

src/CMakeLists.txt

@@ -84,6 +84,12 @@ if(BUILD_SHARED_LIBS)
 	target_compile_definitions("${UCHARDET_LIBRARY}" PUBLIC UCHARDET_SHARED)
 endif()
 
+target_include_directories(${UCHARDET_LIBRARY}
+	PUBLIC
+		"$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>"
+		"$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/${PACKAGE_NAME}>"
+)
+
 if (UCHARDET_STATIC_LIBRARY)
 	add_library(
 		${UCHARDET_STATIC_LIBRARY}
@@ -91,6 +97,12 @@ if (UCHARDET_STATIC_LIBRARY)
 		${UCHARDET_SOURCES}
 	)
 	target_compile_definitions("${UCHARDET_STATIC_LIBRARY}" PRIVATE BUILDING_UCHARDET)
+
+	target_include_directories(${UCHARDET_STATIC_LIBRARY}
+		PUBLIC
+			"$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>"
+			"$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}/${PACKAGE_NAME}>"
+	)
 endif (UCHARDET_STATIC_LIBRARY)
 
 set_target_properties(
@@ -121,6 +133,8 @@ if (NOT WIN32)
 	install(
 		TARGETS
 			${UCHARDET_LIBRARY}
+		EXPORT
+			UchardetTargets
 		LIBRARY DESTINATION
 			${CMAKE_INSTALL_LIBDIR}
 		ARCHIVE DESTINATION
@@ -130,6 +144,8 @@ else (NOT WIN32)
 	install(
 		TARGETS
 			${UCHARDET_LIBRARY}
+		EXPORT
+			UchardetTargets
 		RUNTIME DESTINATION
 			${CMAKE_INSTALL_BINDIR}
 		ARCHIVE DESTINATION
@@ -141,6 +157,8 @@ if (UCHARDET_STATIC_LIBRARY)
 	install(
 		TARGETS
 			${UCHARDET_STATIC_LIBRARY}
+		EXPORT
+			UchardetTargets
 		ARCHIVE DESTINATION
 			${CMAKE_INSTALL_LIBDIR}
 	)

src/tools/CMakeLists.txt

@@ -35,6 +35,8 @@ target_link_libraries(
 install(
 	TARGETS
 		${UCHARDET_BINARY}
+	EXPORT
+		UchardetTargets
 	RUNTIME DESTINATION
 		${CMAKE_INSTALL_BINDIR}
 )

uchardet-config.cmake.in

@@ -0,0 +1,19 @@
+# This file may optionally do:
+#
+# 1. Check for dependencies of exported targets. Example:
+#
+# include(CMakeFindDependencyMacro)
+# find_dependency(MYDEP REQUIRED)
+#
+# find_dependency() has the same syntax as find_package()
+#
+# 2. Capture values from configuration. Example:
+#
+# set(my-config-var @my-config-var@)
+#
+# 3. Other required setup when importing targets from another project
+#
+# See also:
+# https://cliutils.gitlab.io/modern-cmake/chapters/install.html
+#
+include("${CMAKE_CURRENT_LIST_DIR}/uchardet-targets.cmake")