Newest tag across all branches

newestTaggedCommit="$(git rev-list --tags --max-count=1)"
tagName="$(git describe --tags "$newestTaggedCommit")"
# Commits since tag
git log "$(git rev-list --tags --max-count=1)"..HEAD --oneline

https://stackoverflow.com/a/7979255

Newest tag on current branch

newestTagName="$(git describe --tags --abbrev=0)"
# Commits since tag
git log "$(git describe --tags --abbrev=0)"..HEAD --oneline

https://stackoverflow.com/a/12083016

git describe doesn't seem to show tags made on other branches, even if they have been merged in (so follows only the first parent of a merge).

git rev-list --tags seems to be reliable for my use case (we release from different branches).