[ydah]

ConstExprEvaluator applies isset-style fetching only to the outermost array offset on the left of ??. Inner offsets can therefore cause evaluateSilently() to throw instead of returning the fallback:

$expr = $parser->parse('<?php ["a" => 1]["b"]["c"] ?? 2;')[0]->expr;
$evaluator->evaluateSilently($expr);
// Before: exception for undefined key "b"
// After:  2

$expr = $parser->parse('<?php null["a"]["b"] ?? 3;')[0]->expr;
$evaluator->evaluateSilently($expr);
// Before: exception for accessing an offset on null
// After:  3

Propagate isset context through nested array offsets, while evaluating offset expressions normally and preserving right-hand-side short-circuiting.