Bridge bug: PHP filter does not decode \' escape in single-quoted strings

[asgeirf]

Surfaced by the spec contract audit (PR for spec/php).

Symptom

Per the PHP Manual on single quoted strings, inside a single-quoted PHP string the only two escape sequences are \' (literal apostrophe) and \\ (literal backslash). Both should decode to their literal characters in the extracted text.

The Okapi PHPContentFilter keeps the backslash and the apostrophe verbatim instead of decoding \' → '.

Reproduction

core/formats/phpcontent/spec.yaml feature single_quoted_string::escaped_apostrophe:

input:    <?php $text = 'It\'s a test';
expected: It's a test          (native, correct per PHP spec)
bridge:   It\'s a test         (backslash-apostrophe kept verbatim)

Spec tag

The example is tagged expected_fail: in the spec.yaml so the parity gate downgrades it to a warning until the bridge is fixed. Once the bridge fix lands, drop the expected_fail: block.

Repro test

KAPI_PARITY_SANDBOX=$PWD/.parity \
  go test -tags parity -run TestParityPhpSpec/single_quoted_string -count=1 -v ./parity/...

(from cli/, on branch spec/php)

Affected upstream code

okf_phpcontent (okapi-filter-php) — the single-quoted-string lexer in PHPContentFilter, all currently-shipped Okapi versions affected.

[asgeirf]

Moved from neokapi/neokapi#498

Transferred during tracker housekeeping. The defect stays open here rather than being closed: okapi-bridge continues as a standalone product — the reference implementation of a third-party kapi plugin in a non-Go language (neokapi/neokapi#1073) — so a divergence in the okf_phpcontent filter remains actionable independently of what neokapi ships natively.

What changed on the neokapi side

neokapi/neokapi#1079 removed the native phpcontent format package. The reproduction path recorded in the body above therefore no longer resolves:

• core/formats/phpcontent/spec.yaml (and its expected_fail: tag) was deleted with the package
• TestParityPhpSpec and the spec/php branch no longer exist

The report itself is unaffected: its reference point is the PHP language specification for single-quoted strings, where \' and \\ are the only two recognised escape sequences, not a neokapi implementation.

Reproducing here

Exercise net.sf.okapi.filters.php.PHPContentFilter directly from this repository's test suite with <?php $text = 'It\'s a test'; and assert the extracted text is It's a test. Worth pairing with the \\ case, which the same lexer path governs.