export const x = expr as Generic<A, B> produces a phantom export named after B, colliding when 2+ such casts share a last type arg #296

import-in-the-middle's ESM export scanner (lib/get-esm-exports.mjs → es-module-lexer) misparses a specific TypeScript cast shape: export const x = expr as GenericType<Arg1, Arg2>;. When the cast target has 2+ comma-separated type arguments, the scanner emits a phantom second export named after the literal text of the last type argument — not tied to any real binding.

Not specific to the word unknown — swapping it for number produces a phantom number export instead. But unknown is exactly what codegen tools emit as the trailing type arg for typed documents with no variables (e.g. graphql-code-generator's typed-document-node plugin: export const MyQueryDocument = {...} as unknown as DocumentNode<MyQuery, unknown>;). Any generated file with 2+ such exports gets two phantom "unknown" exports, which collide in the generated wrapper module — invalid ESM, crashes the module linker before user code runs:

SyntaxError: Duplicate export of 'unknown'

Repro

Full runnable repro: https://gist.github.com/tmair/a10f56297ca85729faabedc897d47918

git clone https://gist.github.com/a10f56297ca85729faabedc897d47918.git phantom-export

Run:

npm install
node --experimental-loader=import-in-the-middle/hook.mjs --import ./register.mjs app.mjs

Expected: 1

Actual:

file:///.../types.ts?iitm=true:16
export { $0 as "foo", $1 as "unknown", $2 as "bar", $3 as "unknown" }
                                                    ^^^^^^^^^^^^^^^
SyntaxError: Duplicate export of 'unknown'

Environment

• import-in-the-middle: reproduces on 3.5.0 and 3.5.1 (latest)
• Node.js: v26.3.0 locally; also seen on v24.21.0 in production
• Triggered via Node's native TypeScript execution (running .ts files directly, no separate transpile step) combined with --experimental-loader=import-in-the-middle/hook.mjs

Boundary conditions checked

• Single-arg generic cast (1 as Array<unknown>) — no phantom export.
• Type annotation instead of cast (const foo: Generic<A, B> = ...) — no phantom export.
• Only a cast expression as Generic<Arg1, Arg2> with 2+ type args triggers it; phantom export name = last type argument's text.