TypeScript: Index.fts({ language: "english" }) aborts the Node process with an uncatchable panic #4367

Bug bash: Ready to fix

Bug bash priority: High · critical-fix: yes
From the FTS for Code bug bash (2026-10-01), findings: sdkdocs-1.md. Repros ran against released artifacts (pylance 12.0.0 / 13.0.0b18, lancedb 0.39.0 / 0.40.0b12, @lancedb/lancedb 0.40.0-beta.12) unless stated. $S is the bug bash scratch dir.

• Category: bug
• Environment: lancedb TypeScript, local, Node v24.21.0, Linux arm64
• Artifacts: @lancedb/lancedb 0.40.0-beta.12 (lancedb v0.40.0-beta.12, lance v13.0.0-beta.18)
• Target tracker: GitHub lancedb/lancedb

Repro

$S/hunt/sdkdocs/ts/lang.mjs:

import * as lancedb from "@lancedb/lancedb";
import { mkdtempSync } from "node:fs"; import { tmpdir } from "node:os"; import { join } from "node:path";
const which = process.argv[2];
try {
  if (which === "index") {
    const db = await lancedb.connect(mkdtempSync(join(tmpdir(), "ldb-")));
    const t = await db.createTable("t", [{ id: 1, code: "getUserName" }]);
    await t.createIndex("code", { config: lancedb.Index.fts({ baseTokenizer: "code", language: process.argv[3] }) });
  } else {
    console.log(await lancedb.tokenize("running", { language: process.argv[3] }));
  }
} catch (e) { console.log("caught", e.name, e.message); }

$ node lang.mjs index Klingon; echo "exit=$?"
thread '<unnamed>' (95409) panicked at nodejs/src/index.rs:242:45:
called `Result::unwrap()` on an `Err` value: Arrow { message: "unknown variant `Klingon`, expected one of `Arabic`, `Danish`, `Dutch`, `English`, `Finnish`, `French`, `German`, `Greek`, `Hungarian`, `Italian`, `Norwegian`, `Portuguese`, `Romanian`, `Russian`, `Spanish`, `Swedish`, `Tamil`, `Turkish` at line 1 column 9", location: Location { file: ".../lance-8ddea23c38163eda/b646eda/rust/lance-index/src/scalar/inverted/tokenizer.rs", line: 839, column: 24 }, backtrace: MaybeBacktrace }
fatal runtime error: failed to initiate panic, error 622329968, aborting
Aborted                    (core dumped) node lang.mjs index
exit=134

$ node lang.mjs index english      # lowercase is also rejected
thread '<unnamed>' (95790) panicked at nodejs/src/index.rs:242:45:

$ node lang.mjs tok Klingon; echo "exit=$?"
caught Error LanceDB does not support the requested language: 'Klingon'
exit=0

The try/catch never runs: the whole process aborts with core dump (exit 134). The same bad value in lancedb.tokenize throws a normal catchable Error.

Expected behavior

Index.fts throws a catchable JS Error, like lancedb.tokenize does in TS and like Python does:

>>> t.create_fts_index('code', language='english')
ValueError LanceDB does not support the requested language: 'english'

Evidence: Python behavior above (lancedb 0.40.0b12); TS tokenize behavior above. FtsOptions.language is typed as plain string (src/lancedb/nodejs/lancedb/indices.ts:530-533), so TS's type checker can't catch a bad value.

Suspected root cause

src/lancedb/nodejs/src/index.rs:241-243 calls opts.language(&language).unwrap(). FtsIndexBuilder::language returns Err for an unknown language (src/lance/rust/lance-index/src/scalar/inverted/tokenizer.rs:839), and the panic crosses the napi boundary and aborts the process. The function already returns napi::Result<Self> (index.rs:233), so the error can be propagated.

Fix direction

Map the error to napi::Error with ? (same message as Python/tokenize), and add a TS test for an invalid language.