Fix some Doxygen stuff

Author: toroidal-code

CMakeLists.txt

@@ -36,3 +36,52 @@ if(BUILD_EXAMPLES)
     set_property(TARGET cppspec_sample PROPERTY CXX_INCLUDE_WHAT_YOU_USE ${iwyu_path})
   endif()
 endif(BUILD_EXAMPLES)
+
+
+# ##### Documentation generation #######
+# check if Doxygen is installed
+find_package(Doxygen
+    OPTIONAL_COMPONENTS dot mscgen dia
+)
+
+if(DOXYGEN_FOUND)
+    if(NOT ${DOXYGEN_HAVE_DOT})
+        message(
+            "Can't find GraphViz DOT tool for generating images."
+            "Make sure it's on your PATH or install GraphViz")
+    endif()
+
+    cmake_policy(SET CMP0135 NEW)
+
+    include(FetchContent)
+    
+    FetchContent_Declare(doxygen-awesome-css
+      URL      https://github.com/jothepro/doxygen-awesome-css/archive/refs/tags/v2.2.1.tar.gz
+      URL_HASH MD5=340d3a206794ac01a91791c2a513991f
+    )
+    FetchContent_MakeAvailable(doxygen-awesome-css)
+
+    set(DOXYGEN_PROJECT_NAME "C++Spec")
+    set(DOXYGEN_PROJECT_BRIEF "BDD testing for C++")
+    set(DOXYGEN_RECURSIVE YES)
+    set(DOXYGEN_EXAMPLE_RECURSIVE YES)
+
+    set(DOXYGEN_NUM_PROC_THREADS ${HOST_NUM_CORES})
+
+    # From doxygen-awesome
+    set(DOXYGEN_GENERATE_TREEVIEW YES)
+    set(DOXYGEN_DISABLE_INDEX NO)
+    set(DOXYGEN_FULL_SIDEBAR NO)
+    set(DOXYGEN_HTML_COLORSTYLE LIGHT)
+    set(DOXYGEN_HTML_EXTRA_STYLESHEET "${doxygen-awesome-css_SOURCE_DIR}/doxygen-awesome.css")
+
+    set(DOXYGEN_USE_MDFILE_AS_MAINPAGE README.md)
+
+    file(GLOB markdown_SOURCES *.md)
+
+    doxygen_add_docs(doxygen ${markdown_SOURCES} include)
+else(DOXYGEN_FOUND)
+    message(WARNING
+        "Doxygen needs to be installed to generate documentation."
+        "Please install from https://github.com/doxygen/doxygen/releases")
+endif(DOXYGEN_FOUND)