chore: add preprocessor support for doxygen

CMakeLists.txt

@@ -37,6 +37,10 @@ endif ()
 if (YYCC_BUILD_BENCHMARK)
     find_package(benchmark REQUIRED)
 endif ()
+# Doxygen is required if we build doc
+if (YYCC_BUILD_DOC)
+    find_package(Doxygen REQUIRED)
+endif ()
 # Iconv is required if we are not in Windows or user request it
 if (YYCC_ENFORCE_ICONV OR (NOT WIN32))
     find_package(Iconv REQUIRED)

doc/CMakeLists.txt

@@ -1,13 +1,31 @@
-# Configure Doxygen config file
+# Extract all public macros defined in YYCC
+# However, you should note that these extratcted macros have generator expressions.
+get_target_property(YYCC_COMPILE_DEFINITIONS YYCCommonplace COMPILE_DEFINITIONS)
+if (YYCC_COMPILE_DEFINITIONS STREQUAL "YYCC_COMPILE_DEFINITIONS-NOTFOUND")
+    message(FATAL_ERROR "Cannot extract compile definitions from YYCCommonplace.")
+endif ()
+# Convert list to string for expanding in future.
+list(JOIN YYCC_COMPILE_DEFINITIONS " " YYCC_MACRO_GENERATOR_EXPRESSIONS)
+
+# We simply configure Doxygen config file first.
 configure_file(
     ${CMAKE_CURRENT_LIST_DIR}/Doxyfile.in
     ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
     @ONLY
 )
 
-# Add custom target
+# Then we use "file GENERATE" syntax to generate per-config truely Doxyfile used by Doxygen.
+# Because there is no "$<>" syntax in Doxyfile, so we can safely use it.
+# Please note that the generation of "file GENERATE" syntax will be postponed until the build stage.
+file(GENERATE
+    OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/$<CONFIG>/Doxyfile"
+    INPUT "${CMAKE_CURRENT_BINARY_DIR}/Doxyfile"
+    TARGET YYCCommonplace
+)
+
+# Add custom target using per-config Doxyfile
 add_custom_target (YYCCDocumentation
-    doxygen ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
+    Doxygen::doxygen "${CMAKE_CURRENT_BINARY_DIR}/$<CONFIG>/Doxyfile"
     WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
     COMMENT "Generating documentation" VERBATIM
 )

doc/Doxyfile.in

@@ -2306,7 +2306,7 @@ PERLMOD_MAKEVAR_PREFIX =
 # C-preprocessor directives found in the sources and include files.
 # The default value is: YES.
 
-ENABLE_PREPROCESSING   = NO
+ENABLE_PREPROCESSING   = YES
 
 # If the MACRO_EXPANSION tag is set to YES, doxygen will expand all macro names
 # in the source code. If set to NO, only conditional compilation will be
@@ -2356,7 +2356,7 @@ INCLUDE_FILE_PATTERNS  =
 # recursively expanded use the := operator instead of the = operator.
 # This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
 
-PREDEFINED             = YYCC_DOXYGEN
+PREDEFINED             = @YYCC_MACRO_GENERATOR_EXPRESSIONS@
 
 # If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
 # tag can be used to specify a list of macro names that should be expanded. The