Malte UblandClaude Opus 5.5 887aa774e0 Build an empty array literal in a union of array slots at its first arm
`const message: M = { content: [] }` with `content: TextContent[] |
ImageContent[]` threw at run time, `a 'number[]' value is not
representable in the target union`. tsc types an empty literal `never[]`,
whose element has no representation of its own: the literal mapped through
never's f64 element as `number[]`, then the union slot's retag found no
width lift into either array arm and took the stranded-source trap.

An empty array carries no element to select an arm by, and it is the same
value whichever array family stores it, so the literal is built as the
union's FIRST array arm — the rule a lone array slot already states, and
the one the ternary arm and the `?? []` default apply. Both the IR slot
(lowerExprExpecting) and the literal's own type mapping (lowerArrayLiteral)
now state it for any number of array arms; a single array arm keeps the
identical lowering it had. A `never[]` VALUE (an explicitly declared
variable) still maps to `number[]` and keeps its refusal: mapping never's
element globally is a different change.

Corpus: tests/corpus/empty-array-union-slot.ts pins the nested record
field, declarations and reassignment, declared and async returns, ternary
arms (one and both empty), arguments and default parameters, deeper
nesting, a class field, an optional arm, array/Set/Map element slots, a
callback argument, an assertion, and a fresh array per evaluation.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-29 19:11:34 -07:00
2026-10-29 16:39:31 -05:00
2026-10-29 16:39:31 -05:00
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2026-10-29 06:02:00 -05:00
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scriptc

Vercel Labs Experiment npm version: scriptc License: Apache-2.0 npm downloads per month: scriptc

scriptc compiles TypeScript and JavaScript to native executables and WebAssembly. It uses the types checked by the TypeScript compiler to generate machine code, and the output runs without Node.js installed. npm packages your program imports compile along with it. Code scriptc can't compile is reported at build time with a diagnostic and, where available, a rewrite hint.

scriptc is experimental and supports a subset of JavaScript, TypeScript, and Node.js APIs. Run scriptc coverage on an existing program to see how much of it compiles, and see the limitations and Node.js compatibility reference for details.

Installation

Install with Node.js 24 or later and npm:

$ npm install -g scriptc

The installed compiler runs natively on macOS, Linux, and Windows. Node.js is needed only to install it and to run WASI modules with scriptc run. Standalone compiler archives are also available from GitHub Releases.

Building executables requires a linker and the platform SDK or sysroot. See the quickstart for prerequisites and platform support for host requirements, cross-compilation, and WebAssembly.

Build a program

Create hello.ts:

const who = process.argv.length > 2 ? process.argv[2] : "world";
console.log(`hello, ${who}`);

scriptc run compiles the file and runs the result:

$ scriptc run hello.ts
hello, world

scriptc build writes an executable:

$ scriptc build hello.ts -o hello >/dev/null
$ ./hello scriptc
hello, scriptc

These examples use POSIX shell syntax. On Windows, build hello.exe and run it with .\hello.exe.

Use scriptc coverage hello.ts to check what compiles before you build. See coverage reports for details.

Use Node APIs

Supported Node APIs compile to the native runtime. For example, server.ts:

import { createServer } from "node:http";

const server = createServer((req, res) => {
  res.setHeader("content-type", "application/json");
  res.end(JSON.stringify({ path: req.url }));
});

server.listen(8080, () => {
  console.log("listening on http://localhost:8080");
});
$ scriptc build server.ts -o server >/dev/null
$ ./server
listening on http://localhost:8080

Use npm packages

npm packages compile into the executable with your code, so it doesn't read node_modules at runtime.

Create cli.ts:

import pc from "picocolors";

console.log(pc.green("hello from scriptc"));
$ npm install picocolors
$ scriptc build cli.ts -o cli >/dev/null
$ ./cli
hello from scriptc

Package support is partial. See npm dependencies for which packages compile and how to check them.

Documentation

Contributing

See CONTRIBUTING.md for source setup, testing, native artifact builds, and docs development.

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