This implements NixOS/rfcs#136. This issue is agreed-upon by the https://github.com/orgs/NixOS/teams/nix-team.

Only leave these two commands, collapsing the existing ones into them:

• nix hash convert

  
  nix hash convert [--hash-algo (sha256|md5|...)] --from base16|...|sri --to (base64|...) <strings>...
  

  • the current implementation makes --from optional, but we are not quite sure how that works. If it doesn't seem robust, we can make it mandatory instead.

  • --algo is optional but will error if it can't infer from SRI or guess

• nix hash path:

  nix hash path --hash-algo (sha256|md5|...) --to (base16|...|sri) --mode nar|flat|git <path>
  

  • algo is mandatory, any default would be arbitrary
  • collapse modes to nar (serialise the directory as a NAR and hash that), flat (single file, error on directory), git (directory, according to RFC 133)