[keichi]

Problem

Bit fields are deferred until the whole bit group is read. When the group spans into a nest (whose first field is a bit field), the deferred fields are flushed inside the nest's scope. generateAssert and generateFormatter resolved the variable path / this with ctx.generateVariable() at flush time, so they referenced the nested scope instead of the field's own scope.

Repro

new Parser()
  .bit4("x", { assert: 0xa })
  .nest("n", { type: new Parser().bit4("y") })
  .parse(Buffer.from([0xab]));
// Error: Assertion error: vars.n.x is 10

A formatter on x would likewise be called with this bound to vars.n instead of vars.

Fix

generateAssert takes an optional pre-resolved varName and generateFormatter an optional thisVar. generateBit captures both at deferral time and passes them when flushing. Added a regression test.