Introduce the infrastructure for auto-generating API documentation vi…

…a sphinx and doxygen (#383)

* [doxygen] Update doxygen config file

* [doxygen] Make generated pages readable again

* [sphinx] Add baic sphinx setup and make it pick up doxygen output for c++ API

* [sphinx] Make sphinx generate API docs for python bindings

* [doc] Remove no longer necessary html and style files

* Integrate generation back into cmake

* Add a workflow for building the docs

* Make the documentation target depend on the necessary libs

.github/workflows/publish-docs.yml

@@ -0,0 +1,80 @@
+name: publish-doc
+
+on:
+  push:
+    branches:
+       - 'master'
+    tags:
+      - v*-*
+  workflow_dispatch:
+
+concurrency:
+  group: pages
+  cancel-in-progress: true
+
+jobs:
+  build-doc:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+    - uses: cvmfs-contrib/github-action-cvmfs@v3
+    - uses: aidasoft/run-lcg-view@v4
+      with:
+        container: el9
+        view-path: /cvmfs/sw-nightlies.hsf.org/key4hep
+        run: |
+          echo "::group::Install dependencies"
+          python3 -m pip install -r doc/requirements.txt
+          export PATH=/root/.local/bin:$PATH
+          export PYTHONPATH=/root/.local/lib/python3.10/site-packages:$PYTHONPATH
+
+          echo -e "::endgroup::\n::group::Build podio"
+          cmake -B build . --install-prefix=$(pwd)/install \
+                -GNinja -DENABLE_SIO=ON -DENABLE_RNTUPLE=ON \
+                -DBUILD_TESTING=OFF \
+                -DCMAKE_CXX_STANDARD=17
+          cmake --build build --target install
+          export PYTHONPATH=$(pwd)/install/python:$PYTHONPATH
+          export LD_LIBRARY_PATH=$(pwd)/install/lib*/:$LD_LIBRARY_PATH
+          export ROOT_INCLUDE_PATH=$(pwd)/install/include
+
+          echo -e "::endgroup::\n::group::build doc"
+          sphinx-build -M html doc doc_output
+
+    - name: Upload artifact
+      uses: actions/upload-pages-artifact@v3
+      with:
+        path: doc_output/html
+
+  publish-doc:
+    needs: build-doc
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: gh-pages
+      - uses: actions/download-artifact@v4
+        with:
+          name: github-pages
+          path: doc_artifact
+
+      - name: Update documentation
+        env:
+          TARGET_DIR: ${{ github.ref_name }}
+        run: |
+          mkdir -p ${TARGET_DIR}
+          rm -rf ${TARGET_DIR}/*
+          tar -xvf doc_artifact/artifact.tar --directory ${TARGET_DIR}
+          rm -r doc_artifact
+
+      - name: Commit and push changes
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          TARGET_DIR: ${{ github.ref_name }}
+        run: |
+          git config --global user.email ${GITHUB_ACTOR_ID}+${GITHUB_ACTOR}@users.noreply.github.com
+          git config --global user.name ${GITHUB_ACTOR}
+          git add ${TARGET_DIR}
+          git diff-index --quiet HEAD 2>&1 > /dev/null || git commit -m "Update documentation for ${TARGET_DIR}" && git push

.gitignore

@@ -70,6 +70,11 @@ spack*
 /python/podio/__version__.py
 /python/podio_version.py
 
+# Populated by doc generation
+/doc/py_api
+/doc/_build
+/doc/cpp_api/
+
 # CLion artifacts
 .idea/
 cmake-build*/

cmake/FindSphinx.cmake

@@ -0,0 +1,8 @@
+find_program(SPHINX_BUILD_EXECUTABLE
+  NAMES sphinx-build
+  DOC "Path to sphinx-build executable")
+
+include(FindPackageHandleStandardArgs)
+
+# Handle standard arguments to find_package
+find_package_handle_standard_args(Sphinx "Failed to find sphinx executable" SPHINX_BUILD_EXECUTABLE)

cmake/podioDoxygen.cmake

@@ -1,21 +1,21 @@
 find_package(Doxygen)
-if(DOXYGEN_FOUND)
-  # temporarily override the version for doxy generation (for nightly snapshots)
-  set(tmp ${podio_VERSION})
-  if(DOXYVERSION)
-    set(podio_VERSION ${DOXYVERSION})
-  endif()
-  configure_file(${CMAKE_CURRENT_SOURCE_DIR}/doc/Doxyfile.in
-                 ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile @ONLY)
-  configure_file(${CMAKE_CURRENT_SOURCE_DIR}/doc/doxy-boot.js.in
-                 ${PROJECT_BINARY_DIR}/doxygen/html/doxy-boot.js)
-  add_custom_target(doc
-                    ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
-                    WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
-                    COMMENT "Generating API documentation with Doxygen" VERBATIM)
+find_package(Sphinx)
 
-  install( DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/doxygen DESTINATION doxygen OPTIONAL)
-  # revert version to old value
-  set(podio_VERSION ${tmp})
-  unset(tmp)
-endif(DOXYGEN_FOUND)
+if(DOXYGEN_FOUND AND SPHINX_FOUND)
+  set(SPHINX_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/doc/_build)
+
+  add_custom_target(documentation
+                    COMMAND
+                    ${CMAKE_COMMAND} -E env "LD_LIBRARY_PATH=${CMAKE_BINARY_DIR}/src/:$ENV{LD_LIBRARY_PATH};ROOT_INCLUDE_PATH=${CMAKE_SOURCE_DIR}/include;"
+                    ${SPHINX_BUILD_EXECUTABLE} -M html
+                    ${CMAKE_SOURCE_DIR}/doc ${SPHINX_OUTPUT_DIRECTORY}
+                    COMMENT "Building documentation" VERBATIM
+                    DEPENDS podio::podio podio::podioRootIO
+                    )
+
+  install(DIRECTORY ${SPHINX_OUTPUT_DIRECTORY}/
+    DESTINATION ${CMAKE_INSTALL_DOCDIR}
+    OPTIONAL)
+else()
+  message(WARNING "Could not generate documentation because either Doxygen or Sphinx could not be found")
+endif()