feat(build): install/export rules, umbrella header, verified consumer

CMakeLists.txt

@@ -28,8 +28,14 @@ add_library(plot_core
   src/input/controller.cpp
 )
 add_library(plot::core ALIAS plot_core)
+# What the target is called in an installed tree. Without this the export set is
+# namespaced by the target's own name (plot::plot_core), while the build tree --
+# and every consumer, and this project's own comments -- says plot::core.
+set_target_properties(plot_core PROPERTIES EXPORT_NAME core)
 
-target_include_directories(plot_core PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/include")
+target_include_directories(plot_core PUBLIC
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+  $<INSTALL_INTERFACE:include>)
 target_compile_features(plot_core PUBLIC cxx_std_20)
 target_link_libraries(plot_core PRIVATE ${CMAKE_DL_LIBS})
 plot_apply_warnings(plot_core)
@@ -79,3 +85,49 @@ if(PLOT_BUILD_TESTS)
   enable_testing()
   add_subdirectory(tests)
 endif()
+
+# Install and export. The core always goes in; each adapter joins the set only if
+# its toolkit can be re-found on a consumer's machine, which the adapter decided
+# when it was added (plot_record_adapter_export() -- the decisions and the reasons
+# are in the configure log above). plotConfig.cmake then re-finds exactly those
+# toolkits before including the targets file the adapters are described in, so
+# find_package(plot) + target_link_libraries(consumer PRIVATE plot::core) works
+# from an installed prefix with no -I or -L of the consumer's own.
+if(PLOT_INSTALL)
+  # The adapters that could be promised to a consumer, in the order they were
+  # added, and the find_dependency() calls that re-create their toolkits there.
+  get_property(PLOT_ADAPTER_EXPORT_TARGETS GLOBAL PROPERTY PLOT_ADAPTER_EXPORT_TARGETS)
+  # Substituted into plotConfig.cmake below (@PLOT_ADAPTER_DEPENDENCIES@).
+  get_property(PLOT_ADAPTER_DEPENDENCIES GLOBAL PROPERTY PLOT_ADAPTER_DEPENDENCIES)
+
+  include(CMakePackageConfigHelpers)
+
+  # No INCLUDES DESTINATION here: every target already declares
+  # $<INSTALL_INTERFACE:include> in its own target_include_directories(), and
+  # asking for it twice puts the same directory in the export twice.
+  install(TARGETS plot_core ${PLOT_ADAPTER_EXPORT_TARGETS}
+    EXPORT plotTargets
+    ARCHIVE DESTINATION lib
+    LIBRARY DESTINATION lib
+    RUNTIME DESTINATION bin)
+  install(DIRECTORY include/plot DESTINATION include)
+
+  install(EXPORT plotTargets
+    NAMESPACE plot::
+    FILE plotTargets.cmake
+    DESTINATION lib/cmake/plot)
+
+  configure_package_config_file(
+    cmake/plotConfig.cmake.in
+    "${CMAKE_CURRENT_BINARY_DIR}/plotConfig.cmake"
+    INSTALL_DESTINATION lib/cmake/plot)
+  write_basic_package_version_file(
+    "${CMAKE_CURRENT_BINARY_DIR}/plotConfigVersion.cmake"
+    VERSION ${PROJECT_VERSION}
+    COMPATIBILITY SameMajorVersion)
+
+  install(FILES
+    "${CMAKE_CURRENT_BINARY_DIR}/plotConfig.cmake"
+    "${CMAKE_CURRENT_BINARY_DIR}/plotConfigVersion.cmake"
+    DESTINATION lib/cmake/plot)
+endif()