With introduction of mode support to terraform_providers_lock hooks it should be possible to run the hook without terraform_validate when mode=only-check-is-current-lockfile-cross-platform, but it is not working as advertised.

It works as advertised only when lockfile_contains_all_needed_sha returns 0 = when the lock file is valid. If it NOT valid, for example it is missing hash for some platform, the condition

IMHO the condition could be rewritten to:

if [ "$mode" == "only-check-is-current-lockfile-cross-platform" ] ; then
    lockfile_contains_all_needed_sha "$platforms_count"

    exit_code=$?
    return $exit_code
  fi

In this case it could be executed in mode=only-check-is-current-lockfile-cross-platform without running terraform_validate which runs terraform init under the hood.