fix: preserve blank line after inline block comment in stringify

[spokodev]

The bug

A blank line that follows an inline block comment (/* ... */) placed after a comma is silently dropped by stringify. The identical construct with a line comment (// ...) round-trips correctly.

const {parse, stringify} = require('comment-json')

// inline BLOCK comment after the comma, then a blank line:
const input = '{\n  "a": 1, /* x */\n\n  "b": 2\n}'
stringify(parse(input), null, 2) === input
// false -- the blank line before "b" is lost

// CONTROL: identical shape but a LINE comment round-trips fine:
const ctrl = '{\n  "a": 1, // x\n\n  "b": 2\n}'
stringify(parse(ctrl), null, 2) === ctrl
// true

It also reproduces in arrays ([\n 1, /* x */\n\n 2\n]) and collapses multiple blank lines to zero.

Why it is a stringify defect

For both the line- and block-comment inputs, parse produces the same structure. The only difference is the comment type; the BlankLine token in before:b is captured identically in both. Yet it renders only in the line-comment case, so the loss happens purely in stringify.

Root cause

In join(), the one && two branch did:

one + two.trim() + LF + gap

Here two is the rendered before:<key> slot and carries the blank-line count as leading line breaks. two.trim() discards them, and the branch hardcodes a single LF + gap. The line-comment case survives only because process_comments appends a trailing LF after a LineComment, which lands the missing break in one by coincidence; the block-comment case has no such trailing LF, so the blank line is lost.

The fix

Emit the blank lines that two carries beyond those already supplied by the trailing LF + gap and the trailing line breaks of one:

one
  + repeat_line_breaks(
    Math.max(
      count_leading_line_breaks(two)
        - count_trailing_line_breaks(one) - 1,
      0
    ),
    gap
  )
  + two.trim() + LF + gap

count_leading_line_breaks mirrors the existing count_trailing_line_breaks helper. When two carries no extra blank lines the clamp yields 0, so the output is byte-identical to before for every existing case.

Tests

Added three round-trip tests (block after object property, line-comment control, block in array). The block cases fail on master and pass with the fix; the line-comment control passes both ways. The full suite stays green (403 tests, 100% branch coverage on stringify.js).