Nickel: Incorrectly inserts a newline before = in a record field-value pair

[silverraven691]

Describe the bug

To Reproduce
I write this

{
  config
    | {
      labels | { _ : String } = { a = "a", b = "b" },
    }
    | default
    = {},
}

Turns into this after a nickel format

{
  config
    | {
      labels | { _ : String } = { a
          = "a", b
          = "b" },
    }
    | default
    = {},
}

Which then turns into this after a second nickel format

{
  config
    | {
      labels | { _ : String } = {
          a
          = "a",
          b
          = "b"
        },
    }
    | default
    = {},
}

Expected behavior
I expect no changes to happen.

Environment

• Version of the code: Nickel v1.4.1

Additional context
This is stable

{
  config
    | {
      labels | { _ : String } = { a = "a", b = "b" },
    }
    | default
    #
    = {},
}

[Xophmeister]

Thank you for reporting this. Indeed, I can reproduce this and Topiary actually fails with this input, because the idempotency constraint is flaunted (Nickel must disable this).

That record which gets expanded (and ultimately fails) is on a single line, so I would expect no changes to the original input. If it were to span multiple lines, I would expect something like:

{
  a = "a",
  b = "b"
}

...which is clearly not happening, either 😞

I will look into this...

(cc @yannham)

[Xophmeister]

Minimal reproducer:

{
  config
    | { labels = { a = "a" } }
    = {}
}

[Xophmeister]

The erroneous line break that's being added between the record field and the = sign, in the annotation, is due to this rule:

(
  (#scope_id! "annotated_assignment")
  "=" @prepend_spaced_scoped_softline
)

Either this rule is too general, or the scope is too wide...