Reduce indentation in parentheses-wrapped functions

[musjj]

Description

Functions with attribute set arguments should have the same amount of indentation compared to regular single argument functions when wrapped in a pair of parentheses.

Small example input

{
  foo = [
    (bar: {
      baz = "foobar";
    })
    (
      { bar }:
      {
        baz = "foobar";
      }
    )
  ];
}

Expected output

{
  foo = [
    (bar: {
      baz = "foobar";
    })
    ({ bar }: {
      baz = "foobar";
    })
  ];
}

Actual output

{
  foo = [
    (bar: {
      baz = "foobar";
    })
    (
      { bar }:
      {
        baz = "foobar";
      }
    )
  ];
}

[jfly]

Discussed in today's team meeting. Oftentimes, functions with destructured parameters have multiple keys they're plucking out of the attrset. For example, we would reformat this:

(
  { foo, bar, baz }:
  {
    baz = "foobar";
  }
)

To this:

(
  {
    foo,
    bar,
    baz,
  }:
  {
    baz = "foobar";
  }
)

@MattSturgeon points out that if we are not splitting the destructured args into multiple lines (as in the OP's example), we could "absorb" the function with the surrounding parens. We'll leave this open (and mark it approved) in case someone wants to take a crack at this.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/formatting-team-meeting-2026-03-17/76337/1