fix: escape leading # and ! in keys so they round-trip

[mahirhir]

stringify does not escape a # or ! at the start of a key. Since those characters start a comment when they lead a line, parse reads the output back as a comment and drops the pair:

const { parse, stringify } = require('dot-properties')

parse(stringify({ '#x': 'y' })) // => {}  (the key is lost)
parse(stringify({ '!x': 'y' })) // => {}  (the key is lost)

escapeKey already escapes the separator characters (space, =, :) so they survive a round trip. The comment markers have the same problem when they lead a key, so I escape a leading # or ! there too. parse already unescapes \#/\! back to #/!, and java.util.Properties escapes these as well, so the result round-trips and stays consistent with the reference format. They are left untouched elsewhere in the key, since they are only special at the start of a line.

parse(stringify({ '#x': 'y', '!x': 'w' })) // => { '#x': 'y', '!x': 'w' }
stringify([['a#b!c', 'v']])                // => 'a#b!c = v'  (unchanged)

Added a round-trip test in tests/corner-cases.tests.js. The full suite (40 tests, 100% coverage), eslint, and prettier all pass.

[eemeli]

Looks good, thank you for catching this!

See inline for a small tweak.

[eemeli]

This should work as well?

Suggested change

	const escapeKey = key =>
	escape(key).replace(/[ =:]/g, '\\$&').replace(/^[#!]/, '\\$&')
	const escapeKey = key => escape(key).replace(/^[#!]|[ =:]/g, '\\$&')

[mahirhir]

Applied, thanks. Full suite still 100% coverage, 40/40 passing.

[eemeli]

Please fix the code style, and this is good to merge.