How to use doxygen to update the libical API documentation at http://libical.github.io/libical.

Preparations

Make sure you have Doxygen installed; else this will fail.

Then checkout the desired branch (master is for unstable).

Build the documentation

# inside the libical top-level
mkdir build-apidox
cd build-apidox
cmake -G Ninja .. && ninja docs

Look in doxygen.log for warnings and errors. and fix them.

Load the ./apidocs/html/index.html into a web browser and review.

Uploading the new documentation

git checkout gh-pages
cd ..; rm -rf v3/apidocs; cp -dpr build-apidox/apidocs/html v3/apidocs
git add v3/apidocs #make sure to include any newly generated files
  OR
cd ..; rm -rf v4/apidocs; cp -dpr build-apidox/apidocs/html v4/apidocs
git add v4/apidocs #make sure to include any newly generated files
git commit -m "update apidox" --no-verify . && git push
rm -rf build-apidox

View the updates on http://libical.github.io/libical/index.html (might take a couple minutes to update).

Finally

Add the generated build-apidox/libical.tag file to the github release