[DOC] Add Doxygen documentation support (#362)

* [DOC] Add Doxygen documentationsupport

* minor fix

* remove LLVM_INCLUDE_DOCS and MLIR_INCLUDE_DOCS variable

* remove unnessary set(Dot dot)

CMakeLists.txt

@@ -186,11 +186,10 @@ add_subdirectory(tools)
 add_subdirectory(test)
 add_subdirectory(integration_test)
 
-#option(CIRCT_INCLUDE_DOCS "Generate build targets for the CIRCT docs."
-#  ${LLVM_INCLUDE_DOCS} ${MLIR_INCLUDE_DOCS})
-#if (CIRCT_INCLUDE_DOCS)
-#  add_subdirectory(docs)
-#endif()
+option(CIRCT_INCLUDE_DOCS "Generate build targets for the CIRCT docs.")
+if (CIRCT_INCLUDE_DOCS)
+  add_subdirectory(docs)
+endif()
 
 install(DIRECTORY include/circt
   DESTINATION include

docs/CMakeLists.txt

@@ -0,0 +1,20 @@
+include(FindDoxygen)
+if(DOXYGEN_FOUND)
+  set(abs_top_srcdir ${CMAKE_CURRENT_SOURCE_DIR}/..)
+  set(abs_top_builddir ..)
+
+  configure_file(${CMAKE_CURRENT_SOURCE_DIR}/doxygen.cfg.in
+    ${CMAKE_CURRENT_BINARY_DIR}/doxygen.cfg @ONLY)
+  
+  add_custom_target(doxygen-circt
+    COMMAND ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/doxygen.cfg
+    WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+    COMMENT "Generating circt doxygen documentation." VERBATIM)
+        
+  if (CIRCT_BUILD_DOCS)
+    add_dependencies(doxygen doxygen-circt)
+  endif()
+
+  install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/doxygen/html
+    DESTINATION docs/html)
+endif()

docs/doxygen-mainpage.dox

@@ -0,0 +1,16 @@
+/// @mainpage CIRCT
+///
+/// @section main_intro Introduction
+/// Welcome to CIRCT.
+///
+/// This documentation describes both the private and public interface of CIRCT.
+/// There are no instructions here on how to use CIRCT, only the APIs
+/// that make up the software. For usage instructions, please see
+/// the help command.
+///
+/// @section main_caveat Caveat
+/// This documentation is generated directly from the source code with doxygen.
+/// Since CIRCT is constantly under active development, what you're about to
+/// read is out of date! However, it may still be useful since certain portions
+/// of CIRCT are very stable.
+