$ cabal haddock-project
Warning: haddock-project command is experimental, it might break in the future
Up to date
No documentation was generated as this package does not contain a library.
Perhaps you want to use the --haddock-all flag, or one or more of the
--haddock-executables, --haddock-tests, --haddock-benchmarks or
--haddock-internal flags.
$ cabal haddock-project --haddock-all
Error: cabal: unrecognized 'haddock-project' option `--haddock-all'
$ cabal --version
cabal-install version 3.10.3.0
compiled using version 3.10.3.0 of the Cabal library