cmake: fix Doxygen documentation generation + install html & man pages

CMakeLists.txt

@@ -283,17 +283,31 @@ if(PHYSFS_BUILD_DOCS)
         file(APPEND "${PHYSFS_OUTPUT_DOXYFILE}" "\n\n# Below auto-generated by cmake...\n\n")
         file(APPEND "${PHYSFS_OUTPUT_DOXYFILE}" "PROJECT_NUMBER = \"${PHYSFS_VERSION}\"\n")
         file(APPEND "${PHYSFS_OUTPUT_DOXYFILE}" "OUTPUT_DIRECTORY = \"${CMAKE_CURRENT_BINARY_DIR}/docs\"\n")
+        file(APPEND "${PHYSFS_OUTPUT_DOXYFILE}" "INPUT = \"${CMAKE_CURRENT_SOURCE_DIR}/include\"\n")
         file(APPEND "${PHYSFS_OUTPUT_DOXYFILE}" "\n# End auto-generated section.\n\n")
 
         set(PHYSFS_TARGETNAME_DOCS "docs" CACHE STRING "Name of 'docs' build target")
 
-        add_custom_target(
-            ${PHYSFS_TARGETNAME_DOCS}
-            ${DOXYGEN_EXECUTABLE} "${PHYSFS_OUTPUT_DOXYFILE}"
-            WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
+        add_custom_command(
+            OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/docs/html/index.html"
+            COMMAND ${DOXYGEN_EXECUTABLE} "${PHYSFS_OUTPUT_DOXYFILE}"
             COMMENT "Building documentation in 'docs' directory..."
+            DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/include/physfs.h" "${CMAKE_CURRENT_SOURCE_DIR}/docs/Doxyfile"
         )
 
+        add_custom_target(${PHYSFS_TARGETNAME_DOCS} ALL
+            DEPENDS "${CMAKE_CURRENT_BINARY_DIR}/docs/html/index.html"
+        )
+
+        if(NOT PHYSFS_DISABLE_INSTALL)
+            install(DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/docs/html"
+                    DESTINATION "${CMAKE_INSTALL_DATAROOTDIR}/doc/physfs"
+            )
+            install(DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/docs/man"
+                    DESTINATION "${CMAKE_INSTALL_DATAROOTDIR}"
+            )
+        endif()
+
     else()
         message(STATUS "Doxygen not found. You won't be able to build documentation.")
     endif()