build: move unit+quantity feature from xo-observable -> xo-unit

docs/CMakeLists.txt

@@ -0,0 +1,60 @@
+# xo-unit/docs/CMakeLists.txt
+
+# copied from xo-observable/docs/CMakeLists.txt
+
+set(DOX_CONFIG_FILE ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile)
+
+#set(DOX_DEPS ${PROJECT_SOURCE_DIR}/mainpage.dox)   # not yet
+set(DOX_INPUT_DIR ${PROJECT_SOURCE_DIR})
+set(DOX_OUTPUT_DIR ${CMAKE_CURRENT_BINARY_DIR}/dox)
+
+set(DOX_INDEX_FILE ${DOX_OUTPUT_DIR}/html/index.html)
+
+#set(SPHINX_OUTPUT_DIR ${CMAKE_CURRENT_BINARY_DIR}/sphinx/html)
+#set(SPHINX_INDEX_FILE ${SPHINX_OUTPUT_DIR}/index.html)
+#
+## sphinx .rst files reachable from cmake-examples/docs
+#file(GLOB_RECURSE SPHINX_RST_FILES ${CMAKE_CURRENT_SOURCE_DIR} *.rst)
+
+set(ALL_LIBRARY_TARGETS xo_unit)  # todo: automate this from xo-cmake macros
+#set(ALL_UTEST_TARGETS "")        # todo: automate this from xo-cmake macros
+
+# look for doxygen executable
+find_program(DOXYGEN_EXECUTABLE NAMES doxygen REQUIRED)
+message("-- DOXYGEN_EXECUTABLE=${DOXYGEN_EXECUTABLE}")
+
+if (XO_SUBMODULE_BUILD)
+    # in submodule build, rely on toplevel docs/CMakeLists.txt file instead
+else()
+    # build docs starting from here only in standalone build.
+    # otherwise use top-level doxygen setup instead.
+
+    # TODO:
+    # 1. move Doxyfile.in to xo-cmake project
+    # 2. replace this command section with xo-cmake macro
+    #
+    configure_file(
+        Doxyfile.in ${DOX_CONFIG_FILE}
+        FILE_PERMISSIONS OWNER_READ OWNER_EXECUTE GROUP_READ GROUP_EXECUTE WORLD_READ WORLD_EXECUTE
+        @ONLY)
+
+    file(MAKE_DIRECTORY ${DOX_OUTPUT_DIR})
+    add_custom_command(
+        OUTPUT ${DOX_INDEX_FILE}
+        DEPENDS ${DOX_DEPS} ${ALL_LIBRARY_TARGETS} ${ALL_UTEST_TARGETS}
+        COMMAND "${DOXYGEN_EXECUTABLE}" ${DOX_CONFIG_FILE}
+        WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+        MAIN_DEPENDENCY ${DOX_CONFIG_FILE}
+        COMMENT "Generating docs (doxygen)")
+
+    # To build this target
+    #   $ cmake --build .build -j -- doxygen
+    # or
+    #   $ cd .build
+    #   $ make doxygen
+    #
+    add_custom_target(
+        doxygen
+        DEPENDS ${DOX_INDEX_FILE}
+    )
+endif()