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There are many tools for generating completion scripts for shell languages (bash, zsh, fish, etc), crazy-complete is one of the best among such tools.
ldc -h | crazy-complete --input-type=help yaml /dev/stdin > ldc.yaml
crazy-complete --input-type=yaml fish ldc.yaml > ldc.fish
See https://github.com/legendu-net/icon/tree/dev/completion for a real example.