You can not configure the treatment of File.read!/1, as it is not a “local”. :locals_without_parens will only ever work for unqualified calls, those you write without a module in fron tof them.

And parenthesis aren’t really optional, they are considered best practice by the community and most of us actually agree on the formatter in the regard of adding them unconditionally. I’d even consider it a bug, that none are added to split/1.

The main reason why parens have been made optional for the compiler, is probably to make things like def and defmodule writable without having to wrap parenthesis to their arguments.

For those interested, the latest formatter plugin freedom_formatter now has the option to add parenthesis for these calls.

foo |> bar |> baz
# becomes, if `local_pipe_with_parens` option set to `true`:
foo |> bar() |> baz()