Support async_sequence by Bashamega · Pull Request #2533 · microsoft/TypeScript-DOM-lib-generator

Adam Naji (Bashamega) · 2026-08-28T08:16:02Z

closes #2480

…nd maintainability

Kagami Sascha Rosylight (saschanaz) · 2026-08-28T08:20:41Z

Please just do the async_sequence part, the other parts are too big to consume.

Adam Naji (Bashamega) · 2026-08-28T08:26:05Z

Please just do the async_sequence part, the other parts are too big to consume.

Sure, but how can we test it without upgrading the library?

Kagami Sascha Rosylight (saschanaz) · 2026-08-28T08:29:05Z

That's a good question. But it's kinda more important to make the job pass than making it correct right now, we'll get it checked later when we get the actual IDL updated.

Signed-off-by: Bashamega <adambashaahmednaji@gmail.com>

Adam Naji (Bashamega) · 2026-08-28T08:32:51Z

That's a good question. But it's kinda more important to make the job pass than making it correct right now, we'll get it checked later when we get the actual IDL updated.

Done. Thanks for looking at this. When will you check my previous PRs? Or should I close them?

Kagami Sascha Rosylight (saschanaz) · 2026-08-28T08:38:32Z

+          }
+          return "AsyncIterable";
+        } else {
+          // Legacy main & fallback builds: no async iterable interface available.


What is main & fallback builds? Can we say legacy TS versions?

Kagami Sascha Rosylight (saschanaz) · 2026-08-28T08:38:54Z

+        if (compilerBehavior.treatAsyncSequence) {
+          // Forwards-compatible definition:
+          // NOTE: In IDL→TS (whatwg/streams#1372 etc) async_sequence<T> -> AsyncIterable<T>
+          // If stricter interop wanted, could use AsyncIterable<T> | Iterable<T>


Kagami Sascha Rosylight (saschanaz) · 2026-08-28T08:39:42Z

+        // For TS <2.3, the generator separates out [Symbol.asyncIterator] into *.asynciterable.d.ts, so
+        // these references must not leak into the main file, so we can treat them as `any` as a fallback.
+        if (compilerBehavior.treatAsyncSequence) {
+          // Forwards-compatible definition:


forwards-compatible?

Kagami Sascha Rosylight (saschanaz) · 2026-08-28T08:40:18Z

+      // Support async_sequence (see https://github.com/whatwg/streams/pull/1372)
+      if (obj.type === "async_sequence") {
+        // If we're in a build that includes async iterables (TS 2.3+ or forced), emit as AsyncIterable<T>.
+        // For TS <2.3, the generator separates out [Symbol.asyncIterator] into *.asynciterable.d.ts, so


I don't think we care about TS < 2.3, minimum supported version is already 4.4.

That said, AsyncIterable does require separate asynciterable.d.ts until TS 6.0, so to make it correct we need to defer any functions that uses async_sequence to asynciterable variant.

Given we don't really test it here, it's also acceptable to just entirely skip the generation for those functions with some console warning.

I don't think we are doing this?

I don't quite understand this comment but i have pushed a change tell me if this is what you mean

Kagami Sascha Rosylight (saschanaz) · 2026-08-28T08:41:48Z

      outputFolder: new URL("./ts5.5/", outputFolder),
-      compilerBehavior: {}, // ts5.5 does not support `IteratorObject` or unrelated setter types
+      compilerBehavior: {
+        treatAsyncSequence: false,


Let it just empty as others did here

Adam Naji (Bashamega) · 2026-08-28T09:30:18Z

done

… warn for TypeScript versions below 6.0

Kagami Sascha Rosylight (saschanaz) · 2026-08-28T11:08:26Z

      compilerBehavior: {
        useIteratorObject: true,
        allowUnrelatedSetterType: true,
+        treatAsyncSequence: false,


Again, please skip it as others do

Sorry, done

…unction

Kagami Sascha Rosylight (saschanaz) · 2026-08-28T20:55:34Z

    const type = convertBaseType();
+    if (type === "any") {
+      return type;
+    }


Does this still matter?

…ine type conversion process

Kagami Sascha Rosylight (saschanaz) · 2026-08-30T15:15:17Z

Thanks!

For future reference - I think the fix is in a wrong place - Ideally it should be somewhere in emitMethod or the caller of emitMethod, check the return type from there, and skip the emission for older TS versions. We should not emit any because that's unrecoverable with overloads.

But for now this is okay as we'll check it later.

LGTM

github-actions · 2026-08-30T15:15:34Z

Merging because Kagami Sascha Rosylight (@saschanaz) is a code-owner of all the changes - thanks!

Kagami Sascha Rosylight (saschanaz) · 2026-08-30T15:19:21Z

As for future work - I think it would be nice to consume each of webref/idl and BCD updates release-by-release to reduce #2495 and eventually close it.

About KDL work - I have been thinking of having a library - https://codeberg.org/krosylight/kdl2json, but hasn't been made any progress recently. I was thinking maybe I should encourage contribution once I get it more in form, but any help (or any question for future direction to contribute for) would be nice.

Adam Naji (Bashamega) · 2026-08-30T16:13:26Z

As for future work - I think it would be nice to consume each of webref/idl and BCD updates release-by-release to reduce #2495 and eventually close it.

About KDL work - I have been thinking of having a library - https://codeberg.org/krosylight/kdl2json, but hasn't been made any progress recently. I was thinking maybe I should encourage contribution once I get it more in form, but any help (or any question for future direction to contribute for) would be nice.

Hello,
Thank you for sharing this with me.
I would love to help you out.
Please tell me how I can help out with the kdl2json library. Meanwhile I will try to reduce the pr.

Update Bcd & support async_sequence

9817d72

github-actions Bot added the maintainers label Aug 28, 2026

github-actions Bot assigned Jake Bailey (jakebailey) and Nathan Shively-Sanders (sandersn) Aug 28, 2026

Adam Naji (Bashamega) added 2 commits August 28, 2026 11:18

Refactor async sequence handling in emitWebIdl function for clarity a…

28414b8

…nd maintainability

Update @mdn/browser-compat-data dependency to version 8.0.1

c2020ab

Adam Naji (Bashamega) added 2 commits August 28, 2026 11:30

-

7cc9bb8

Signed-off-by: Bashamega <adambashaahmednaji@gmail.com>

Reset package lock

eabe67c

Signed-off-by: Bashamega <adambashaahmednaji@gmail.com>

Adam Naji (Bashamega) changed the title ~~Update Bcd & support async_sequence~~ Support async_sequence Aug 28, 2026

Kagami Sascha Rosylight (saschanaz) suggested changes Aug 28, 2026

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Adam Naji (Bashamega) added 2 commits August 28, 2026 12:40

Refactor async_sequence handling in emitWebIdl to skip generation and…

afc9000

… warn for TypeScript versions below 6.0

lint

f47f00a

Kagami Sascha Rosylight (saschanaz) reviewed Aug 28, 2026

View reviewed changes

Remove 'treatAsyncSequence' option from compilerBehavior in emitDom f…

afb7d5a

…unction

Kagami Sascha Rosylight (saschanaz) reviewed Aug 28, 2026

View reviewed changes

Adam Naji (Bashamega) and others added 2 commits August 29, 2026 08:39

Remove unnecessary 'any' type check in emitWebIdl function to streaml…

cfb0452

…ine type conversion process

Remove unnecessary line break in emitter.ts

18a1c91

github-actions Bot merged commit 23be9eb into microsoft:main Aug 30, 2026
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Kagami Sascha Rosylight (saschanaz) deleted the feat/update-bcd branch August 30, 2026 15:15

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Adam Naji (Bashamega) commented Aug 28, 2026

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Kagami Sascha Rosylight (saschanaz) commented Aug 30, 2026

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