improve doxygen builds

CMakeLists.txt

@@ -95,12 +95,25 @@ set(LOCALE $ENV{LANG}
 
 # documentation and doxygen setup
 set(PROJECT_DOCS_DIR ${CMAKE_BINARY_DIR}/docs)
-find_program(HAVE_DOXYGEN NAMES doxygen)
-if(HAVE_DOXYGEN)
+include(FindDoxygen QUIET)
+if(DOXYGEN_FOUND)
   configure_file(${PROJECT_SOURCE_DIR}/tools/doxygen/Doxyfile.in ${CMAKE_BINARY_DIR}/tools/doxygen/Doxyfile)
 
+  file(GLOB_RECURSE DOXYGEN_PUBLIC_HEADERS ${PROJECT_SOURCE_DIR}/include/stumpless/*.h)
+  set(EXAMPLE_SOURCES
+    ${PROJECT_SOURCE_DIR}/docs/examples/basic/basic_example.c
+  )
+
   add_custom_target(docs
-    COMMAND doxygen ${CMAKE_BINARY_DIR}/tools/doxygen/Doxyfile
+    COMMAND ${DOXYGEN_EXECUTABLE} ${CMAKE_BINARY_DIR}/tools/doxygen/Doxyfile
+    DEPENDS
+      ${CMAKE_BINARY_DIR}/tools/doxygen/Doxyfile
+      ${DOXYGEN_PUBLIC_HEADERS}
+      ${EXAMPLE_SOURCES}
+      ${PROJECT_SOURCE_DIR}/include/stumpless.h
+      ${CMAKE_BINARY_DIR}/include/stumpless/config.h
+    BYPRODUCTS
+      ${PROJECT_BINARY_DIR}/docs/man/man3/config.h.3
   )
 
   set(INCLUDE_MANPAGES_IN_INSTALL INSTALL_MANPAGES)