WDYT about making it the same option as allowing e.g.

function(x) AWrapper(
  y,
  x
)

?

Wouldn't that disable that particular lint completely?

No, there's still

function(x)
  AWrapper(y, x)

function(x)
  AWrapper(
    y,
    x
  )

Ah okay. Any ideas for an option name? allow_simple_multiline = FALSE is what comes to my mind, but I'm not really happy with it.

But omitting braces here reduces readability, since the reader now needs to mentally add those braces back in.

function() function(x) {
  x
}

Why should we make an exception for such an omission? That is, why is it so important here to leave out braces?

Because you need two additional lines and an additional level of indent.
Not arguing that this should be default, but if you define a bunch of function factories, you end up with a lot of essentially empty lines and reduced available line width for the actual implementations.

Agree it can be useful, and warrants an argument, but also that it should not be the default choice.

Okay, thanks for the explaining. Makes sense.

As for the parameter name, how about curly_braces_required (default: TRUE)?

is strict=TRUE too glib?

strict sounds okay, while not very specific. curly_braces_required would suggest that the other examples mentioned by @MichaelChirico don't lint, which they always should.