Fix unstable assignment when a member chain object has a leading comment - #19882

Description

Fixes #10851.

A comment on the object of a member chain is printed before the whole chain, because the printer adds the parentheses and printComments then wraps the result:

const generate = (
  // @ts-expect-error requireOutside Babel transform
  requireOutside("@babel/generator") as typeof import("@babel/generator")
).default;

After one format the comment leads the right-hand side, which is a state the original source was not in:

const generate = // @ts-expect-error requireOutside Babel transform
(requireOutside("@babel/generator") as typeof import("@babel/generator"))
  .default;

So the second format takes a different branch — hasLeadingOwnLineComment is now true, chooseLayout returns break-after-operator, and the value is indented. Two formats, two outputs.

chooseLayout now looks down the member chain for that comment, so the first format already produces what the second one would:

const generate =
  // @ts-expect-error requireOutside Babel transform
  (requireOutside("@babel/generator") as typeof import("@babel/generator"))
    .default;

This also puts the @ts-expect-error back above the line it suppresses, rather than leaving it stranded after the =.

The same shape shows up whenever the object needs parentheses — as, await, and binary expressions all reproduce it, and all three are covered in the fixture.

Worth flagging

The one existing snapshot this changes, typescript/prettier-ignore/issue-14238.ts, was recording the unstable output:

export const foo = // prettier-ignore
(bar as Baz).qux;

Feeding that text back through main gives a different result, so that snapshot could not survive a second format either. It now records the stable form.

I did not touch the parenthesis/comment ordering in ast-to-doc.js, which is where the comment actually moves. That looked like a much larger change than the bug warranted, and this fix makes the output stable without it — but if you would rather see it solved there, say so and I will look.

Checklist

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