Explicit resource management still not working natively due to SWC transpilation

[nktpro]

Version: Deno 2.2.11

Despite --js-explicit-resource-management v8 flag enabled by default since 2.2.10, the (now obsolete) explicit_resource_management SWC transpilation transformer was not disabled for TypeScript sources. Consequently, TypeScript scripts run with deno still do not benefit from this natively.

Here's a reproducer:

// test.ts
try {
  using _foo = {
    [Symbol.dispose]() {
      throw new Error("foo");
    },
  };

  throw new Error("bar");
} catch (e) {
  console.log(e);
}

deno run test.ts

Outputs:

SuppressedError: An error was suppressed during disposal.
    at fail (file:///test.ts:41:34)
    at next (file:///test.ts:57:11)
    at _ts_dispose_resources (file:///test.ts:63:12)
    at _ts_dispose_resources (file:///test.ts:64:5)
    at file:///test.ts:8:19

The stack trace clearly shows transpiled code with _ts_dispose_resources, which comes from SWC helpers, so the disposal execution actually doesn't leverage v8 natively at all.

On the other hand, if we rename test.ts to test.js, no transpilation occurs, and it works natively as expected:

deno run test.js

Outputs:

SuppressedError: An error was suppressed during disposal
    at file:///test.js:8:3

[0f-0b]

The transpilation step wasn't completely removed because the native implementation had a bug that can cause silent resource leaks—the following code should print dispose but instead prints nothing.

using _ = {
  [Symbol.dispose]() {
    console.log("dispose");
  },
};

(() => _);

(source)

[nktpro]

@0f-0b thank you for that info!

In the case of deno run with a JS file, since it doesn't go through TS transpilation, unfortunately, it's still affected by the v8 bug you mentioned, regardless of the swc rollback.

Hopefully the v8 fix lands in deno core soon...