Investigated the USE_SWIG module src, there isn't a way to tell it no…

…t to compile the SWIG outputs.

Therefore I implmented this which uses a custom command.

I cautiously think it works, although will require some refactoring and refinement.

cmake/doxygen.cmake

@@ -18,33 +18,159 @@ else()
 endif()
 
 macro(create_pydoxygen_target FLAMEGPU_ROOT DOXY_OUT_DIR XML_PATH)
-        # Seperate doxygen target for pyflamegpu
-        if(NOT TARGET pyflamegpu)
-            # create pyflamegpu.py ourselves
-            add_subdirectory(${FLAMEGPU_ROOT}/swig)
+        # Py docs, needs SWIG to convert the .i file/s to .py
+        # We don't require compilation of this file, as performed by UseSWIG module, so we will create a seperate target
+        # So we create a minimal SWIG target ourselves pyflamegpu.py ourselves
+        if(NOT SWIG_FOUND)
+            find_package(SWIG ${SWIG_MINIMUM_SUPPORTED_VERSION})
+            # Borrowed from swig/CMakeLists.txt, should really move it to a module or something.
+            # If minimum required swig could not be found, download and build it.
+            if(NOT SWIG_FOUND)
+                # SWIG_DIR and SWIG_EXECUTABLE are used by FindSwig. Executable specifies version info etc, swig_dir should contain swig.swg (i.e the value of swig -swiglib so doesn't need specifying if teh swig install is good?)
+
+                # Unset swig related variables from the previous failed attempt at finding swig
+                unset(SWIG_FOUND)
+                unset(SWIG_VERSION)
+                unset(SWIG_DIR)
+                unset(SWIG_EXECUTABLE)
+                unset(SWIG_FOUND CACHE)
+                unset(SWIG_VERSION CACHE)
+                unset(SWIG_DIR CACHE)
+                unset(SWIG_EXECUTABLE CACHE)
+
+
+                if(WIN32)
+                    # Download pre-compiled swig on windows.
+                    FetchContent_Declare(
+                        swig
+                        URL      http://prdownloads.sourceforge.net/swig/swigwin-${SWIG_DOWNLOAD_VERSION}.zip
+                        # URL_HASH #@todo - make sure the hash of the download is good?
+                    )
+                    FetchContent_GetProperties(swig)
+                    if(NOT swig_POPULATED)
+                        message(STATUS "[swig] Downloading swigwin-${SWIG_DOWNLOAD_VERSION}.zip")
+                        # Download
+                        FetchContent_Populate(swig)
+
+                        # Set variables used by find_swig to find swig.
+                        # Set locally and in the cache for subsequent invocations of CMake
+                        set(SWIG_EXECUTABLE "${swig_SOURCE_DIR}/swig.exe")
+                        set(SWIG_EXECUTABLE "${swig_SOURCE_DIR}/swig.exe" CACHE FILEPATH "Path to SWIG executable")
+                    endif()
+                else()
+                    # Under linux, download the .tar.gz, extract, build and install.
+                    # This must be done at configure time, as FindSwig requires the swig executable.
+                    # FetchContent allows download at configure time, but must use execute_process to run commands at configure time.
+
+                    # Download from sourceforge not github, github releases require several extra tools to build (bison, yacc, autoconfigure, automake), and we want to keep dependencies light. 
+                    FetchContent_Declare(
+                        swig
+                        URL      https://downloads.sourceforge.net/project/swig/swig/swig-${SWIG_DOWNLOAD_VERSION}/swig-${SWIG_DOWNLOAD_VERSION}.tar.gz
+                        # URL_HASH #@todo - make sure the hash of the download is good?
+                    )
+                    FetchContent_GetProperties(swig)
+                    if(NOT swig_POPULATED)
+                        message(STATUS "[swig] Downloading swig-${SWIG_DOWNLOAD_VERSION}.tar.gz")
+                        # Download the content
+                        FetchContent_Populate(swig)
+
+                        # Set some paths for error files in case things go wrong.
+                        set(swig_configure_ERROR_FILE "${swig_BINARY_DIR}/swig-error-configue.log")
+                        set(swig_make_ERROR_FILE "${swig_BINARY_DIR}/swig-error-make.log")
+                        set(swig_makeinstall_ERROR_FILE "${swig_BINARY_DIR}/swig-error-make-install.log")
+
+                        # run ./configure with an appropraite prefix to install into the _deps/swig-bin directory
+                        message(STATUS "[swig] ./configure --prefix ${swig_BINARY_DIR}")
+                        execute_process(
+                            COMMAND "./configure" "--prefix" "${swig_BINARY_DIR}"
+                            WORKING_DIRECTORY ${swig_SOURCE_DIR}
+                            RESULT_VARIABLE swig_configure_RESULT
+                            OUTPUT_VARIABLE swig_configure_OUTPUT
+                            ERROR_FILE ${swig_configure_ERROR_FILE}
+                        )
+                        if(NOT swig_configure_RESULT EQUAL "0")
+                            message(FATAL_ERROR 
+                            " [swig] Error configuring SWIG ${SWIG_DOWNLOAD_VERSION}.\n"
+                            " Error log: ${swig_configure_ERROR_FILE}\n"
+                            " Consider installing SWIG ${SWIG_MINIMUM_SUPPORTED_VERSION} yourself and passing -DSWIG_EXECUTABLE=/path/to/swig.")
+                        endif()
+
+                        # run make to compile swig within swig_SOURCE_DIR
+                        message(STATUS "[swig] make")
+                        execute_process(
+                            COMMAND "make"
+                            WORKING_DIRECTORY ${swig_SOURCE_DIR}
+                            RESULT_VARIABLE swig_make_RESULT
+                            OUTPUT_VARIABLE swig_make_OUTPUT
+                        )
+                        if(NOT swig_make_RESULT EQUAL "0")
+                            message(FATAL_ERROR 
+                            " [swig] Error compiling SWIG ${SWIG_DOWNLOAD_VERSION}\n"
+                            " Error log: ${swig_make_ERROR_FILE}"
+                            " Consider installing SWIG >= ${SWIG_MINIMUM_SUPPORTED_VERSION} yourself and passing -DSWIG_EXECUTABLE=/path/to/swig.")
+                        endif()
+
+                        # run make install to copy to the installation location (swig_BINARY_DIR)
+                        message(STATUS "[swig] make install")
+                        execute_process(
+                            COMMAND "make" "install"
+                            WORKING_DIRECTORY ${swig_SOURCE_DIR}
+                            RESULT_VARIABLE swig_makeinstall_RESULT
+                            OUTPUT_VARIABLE swig_makeinstall_OUTPUT
+                        )
+                        if(NOT swig_makeinstall_RESULT EQUAL "0")
+                            message(FATAL_ERROR 
+                            " [swig] Error installing SWIG ${SWIG_DOWNLOAD_VERSION}\n"
+                            " Error log: ${swig_makeinstall_ERROR_FILE}"
+                            " Consider installing SWIG >= ${SWIG_MINIMUM_SUPPORTED_VERSION} yourself and passing -DSWIG_EXECUTABLE=/path/to/swig.")
+                        endif()
+
+                        # Set variables used by find_swig to find swig.
+                        # Set locally and in the cache for subsequent invocations of CMake
+                        set(SWIG_EXECUTABLE "${swig_BINARY_DIR}/bin/swig")
+                        set(SWIG_EXECUTABLE "${swig_BINARY_DIR}/bin/swig" CACHE FILEPATH "Path to SWIG executable")
+                    endif()
+                endif()
+                # Attempt to find swig again, but as REQUIRED.
+                find_package(SWIG ${SWIG_MINIMUM_SUPPORTED_VERSION} REQUIRED)
+            endif()
+        endif()
+#"C:\Program Files\CMake\bin\cmake.exe" -E make_directory C:/Users/Robadob/fgpu2/build/swig/python//pyflamegpu C:/Users/Robadob/fgpu2/build/swig/python//pyflamegpu
+#if %errorlevel% neq 0 goto :cmEnd
+#"C:\Program Files\CMake\bin\cmake.exe" -E env SWIG_LIB=C:/Users/Robadob/fgpu2/build/_deps/swig-src/Lib C:/Users/Robadob/fgpu2/build/_deps/swig-src/swig.exe -python -doxygen -IC:/Users/Robadob/fgpu2/include -IC:/ProgramData/Anaconda3/include -IC:/Users/Robadob/fgpu2_vis/include "-IC:/Program Files/NVIDIA GPU Computing Toolkit/CUDA/v11.2/include" -IC:/Users/Robadob/fgpu2/build/_deps/jitify-src -IC:/Users/Robadob/fgpu2/include -IC:/Users/Robadob/fgpu2/build/FLAMEGPU2/_deps/flamegpu2_visualiser-build/freetype-build/include -IC:/Users/Robadob/fgpu2/build/FLAMEGPU2/_deps/flamegpu2_visualiser-build/freetype-src/include -IC:/Users/Robadob/fgpu2/build/_cmrc/include -IC:/Users/Robadob/fgpu2/build/_deps/thrust-src/dependencies/cub -IC:/Users/Robadob/fgpu2/build/_deps/thrust-src -IC:/Users/Robadob/fgpu2/build/_deps/tinyxml2-src -DVISUALISATION -DSEATBELTS=1 -DNOMINMAX -threads -outdir C:/Users/Robadob/fgpu2/build/swig/python//pyflamegpu -c++ -module pyflamegpu -interface _pyflamegpu -o C:/Users/Robadob/fgpu2/build/swig/python//pyflamegpu/flamegpuPYTHON_wrap.cxx C:/Users/Robadob/fgpu2/swig/python/flamegpu.i
+        if(SEATBELTS)
+          set(DEFINE_SEATBELTS "-DSEATBELTS=1")
+        endif()
+        if(VISUALISATION)
+          set(DEFINE_VISUALISATION "-I${VISUALISATION_ROOT}/include -DVISUALISATION")
         endif()
-        SET(PYTHON_LIB_TEMP_DIRECTORY ${CMAKE_BINARY_DIR}/swig/python/${CMAKE_BUILD_TYPE})
-        set(DOXYGEN_STRIP_FROM_PATH       "${PYTHON_LIB_TEMP_DIRECTORY}/pyflamegpu")
-        set(DOXYGEN_STRIP_FROM_INC_PATH   "${PYTHON_LIB_TEMP_DIRECTORY}/pyflamegpu")
+        add_custom_target(
+            pyflamegpu_pyonly
+            COMMAND ${CMAKE_COMMAND} -E make_directory "${CMAKE_BINARY_DIR}/pyflamegpu_docs"
+            COMMAND ${CMAKE_COMMAND} -E env "SWIG_LIB=${SWIG_DIR}" ${SWIG_EXECUTABLE} -python -doxygen "-I${FLAMEGPU_ROOT}/include" ${DEFINE_VISUALISATION} ${DEFINE_SEATBELTS} -DNOMINMAX -threads -outdir "${CMAKE_BINARY_DIR}/pyflamegpu_docs" -c++ -module pyflamegpu -interface _pyflamegpu -o flamegpuPYTHON_wrap.cxx "${FLAMEGPU_ROOT}/swig/python/flamegpu.i"
+        )
+        # And now do the doxygen bits
+        set(DOXYGEN_STRIP_FROM_PATH       "${CMAKE_BINARY_DIR}/pyflamegpu_docs")
+        set(DOXYGEN_STRIP_FROM_INC_PATH   "${CMAKE_BINARY_DIR}/pyflamegpu_docs")
         set(DOXYGEN_PREDEFINED            "")
         set(DOXYGEN_PYTHON_DOCSTRING      NO)
-        set(DOXY_INPUT_FILES "${PYTHON_LIB_TEMP_DIRECTORY}/pyflamegpu/pyflamegpu.py")
+        set(DOXY_INPUT_FILES "${CMAKE_BINARY_DIR}/pyflamegpu_docs/pyflamegpu.py")
         if("${XML_PATH}" STREQUAL "")
             doxygen_add_docs("pydocs" "${DOXY_INPUT_FILES}")
-            add_dependencies("pydocs" "pyflamegpu")
             set_target_properties("pydocs" PROPERTIES EXCLUDE_FROM_ALL TRUE)
             if(COMMAND CMAKE_SET_TARGET_FOLDER)
                 # Put within FLAMEGPU filter
                 CMAKE_SET_TARGET_FOLDER("pydocs" "FLAMEGPU")
             endif()
+            add_dependencies(pydocs pyflamegpu_pyonly)
         else()
             doxygen_add_docs("api_pydocs_xml" "${DOXY_INPUT_FILES}")
-            add_dependencies("api_pydocs_xml" "pyflamegpu")
             set_target_properties("api_pydocs_xml" PROPERTIES EXCLUDE_FROM_ALL TRUE)
             if(COMMAND CMAKE_SET_TARGET_FOLDER)
                 # Put within FLAMEGPU filter
                 CMAKE_SET_TARGET_FOLDER("api_pydocs_xml" "FLAMEGPU")
             endif()
+            add_dependencies(api_pydocs_xml pyflamegpu_pyonly)
         endif()
 endmacro()