A datatype named __proto__, constructor, or toString crashes both emitters through the inherited WORDS lookup

[jasisz]

What you did

bun bend2/main.ts proto_type.bend --check-only
bun bend2/main.ts proto_type.bend
bun bend2/main.ts proto_type.bend -o out.js
bun bend2/main.ts proto_type.bend -o out

proto_type.bend:

import Base

type __proto__ is Data:
  P{}

def main() -> __proto__:
  P{}

What happened

The checker accepts the file and the interpreter prints the expected value:

All terms check.
P{}

Both the JS and native build paths instead fail inside the compiler:

TypeError: undefined is not an object (evaluating 'lay.ks.length')

Why it happens

WORDS is a normal object, but datatype names are used to query it without an own-property check:

const WORDS: Record<string, Lay> = { U32: W32, F32: W32, Nat: W64 };

function lay_of(book: Bend.Book, A: HTerm | null): Lay {
  const t = ty_adt(book, A);
  if (t === null) {
    return BOX;
  }
  return WORDS[t.k] ?? memo(LAYS, A!, () => {

For __proto__, WORDS[t.k] returns the inherited Object.prototype rather than undefined, so lay_of returns a value that is not a Lay; the printer/layout path later reads its nonexistent ks. The same bug reproduces with datatypes named constructor and toString, confirming that this is the inherited-property class rather than a special parser case.

The compiler already gives the user-indexed OPERATIONS and OPTIMIZED tables null prototypes. WORDS needs the same treatment, or each lookup needs to require an own property.

This also reproduces on 2.0.23, so it is not a 2.0.24 regression.

bend --version

bend 2.0.24
commit 99f9c6cd

uname -sm

Darwin arm64

clang --version (the first line)

Apple clang version 21.0.0 (clang-2100.0.123.102)

[VictorTaelin]

Fixed in 2.0.25: WORDS has a null prototype now, and the printer's kind table (the same bug) is a list lookup. __proto__, constructor and toString as type and field names print on all three lanes. Pinned as tests/compile/proto_type_name.bend. Thank you.

Note: this reply was written by an AI after it reported the issue to me and I made the decision. If anything here is wrong, reply and I will review it myself.