test262 annexB legacy-web tail (73) — RegExp legacy escapes (\1 backref, \c control) + B.3.x function-binding semantics

[proggeramlug]

Measured 2026-06-23 on an internal Linux sweep host (perry 0.5.1204, node v26.3.0); persistent standing gap (the 2026-06-23 regression #5579 excluded). Split from now-closed umbrella #5346. See test-compat/test262/README.md.

73 failing (test262 @ 2026-06-23 sweep).

Top reasons

n	reason
14	SameValue(«Another function») block-fn hoisting
6	binding is not initialized to undefined
6	ReferenceError: f is not defined
6	SameValue(«first declaration»)
6	SameValue(«undefined» vs «function»)
2	Invalid regular expression: /\1/ legacy backref/octal
2	/\cА/ control escape

Sample tests

annexB/built-ins/RegExp/RegExp-leading-escape.js
annexB/built-ins/RegExp/RegExp-decimal-escape-not-capturing.js
annexB/built-ins/RegExp/RegExp-control-escape-russian-letter.js
annexB/language/...

Two concrete subclusters: (1) Annex B legacy RegExp escapes — \1 as octal/identity when no such capture group, \c<letter> control escapes — Perry rejects these as invalid patterns (Rust regex crate strictness); (2) B.3.3 residual block-scoped function-declaration hoisting edge cases (f is not defined / binding-init).

Measure

scripts/test262_subset.py --root /root/test262 --dir annexB --jobs 6

[proggeramlug]

Re-measure 2026-06-25 (main @ 9a3d246): annexB tail → 39 (legacy escapes + B.3.3 fixed).