[Fix] parse: a backslash inside single quotes must not escape the closing quote

[mahirhir]

In a POSIX shell a single-quoted string is fully literal: a backslash inside single quotes is just a backslash and never escapes the closing quote. parse's scanner already follows this (rule 1 in the comment in parse.js; the single-quote branch only does out += c), but the chunker regex that splits the input into tokens does not.

The single-quote matcher is:

var DOUBLE_QUOTE = '\'((\\\\\'|[^\'])*?)\'';

The \' alternative lets the regex treat a backslash-then-quote as an escaped quote inside a single-quoted token, so it walks past the real closing quote and keeps consuming the trailing whitespace and the next token. Two single-quoted tokens that end in a backslash get merged into one:

parse("'\\' '\\'")   // returns ["\\ \\"]  (one token); expected ["\\", "\\"]

This also breaks round-tripping through quote. Since #20, quote wraps a backslash in single quotes without escaping it (quote(["\\"]) === "'\\'"), which is correct, but parse cannot read its own output back:

parse(quote(["\\", "\\"]))   // returns ["\\ \\"]; expected ["\\", "\\"]

The fix drops the \' alternative so the single-quote matcher ends at the first closing quote, matching the scanner and POSIX:

var DOUBLE_QUOTE = '\'([^\']*?)\'';

The normal way to place a quote next to single-quoted text, '\'' (close, escaped quote, reopen), is unaffected: parse("'\\'\\''") still returns ["\\'"].

Added three assertions in test/parse.js (the two-token case, the quote/parse round-trip, and the '\'' preservation case). The full suite passes. Reverting only the parse.js change makes the two behavioral assertions fail.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.40%. Comparing base (d390f9a) to head (5d460a3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #26   +/-   ##
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  Coverage   99.40%   99.40%           
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  Files           3        3           
  Lines         168      168           
  Branches       48       48           
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  Hits          167      167           
  Misses          1        1           

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