Bun includes a TypeScript -> JavaScript transpiler, which is used
to power the runtime (run .ts files directly). It can be run in isolation
with the CLI command bun build ./input.ts (default output to stdout).
The bug comes from transpiling TypeScript enums inside of namespaces.
JavaScript has neither enum nor namespace, so it's the transpiler's job
to lower this syntax into valid JavaScript.
Given the input:
namespace Test {
export enum Foo {}
}Bun currently outputs the following, which when run throws a syntax error:
// test.ts
var Test;
(function (Test) {
export let Foo; // <-- SyntaxError: unexpected`export`
(function (Foo2) {})((Foo = Test.Foo || (Test.Foo = {})));
})(Test || (Test = {}));It is worth noting that parser/transpiler in Bun was originally written by porting esbuild to Zig, with many functions names being identical, down to copying some of their comments. Esbuild does not have this bug.
Bun can be rebuild with ninja -Cbuild, where it is available as bun-debug.
VSCode's debugger has been configured to run bun-debug build on the sample
file for you.