Support async_sequence

src/build.ts

@@ -252,6 +252,7 @@ async function emitDom() {
         allowUnrelatedSetterType: true,
         useGenericTypedArrays: true,
         includeIterable: true,
+        treatAsyncSequence: true,
       },
     },
     // ts5.7 (and later)
@@ -262,6 +263,7 @@ async function emitDom() {
         useIteratorObject: true,
         allowUnrelatedSetterType: true,
         useGenericTypedArrays: true,
+        treatAsyncSequence: true,
       },
     },
     // ts5.6

src/build/emitter.ts

@@ -132,6 +132,8 @@ export interface CompilerBehavior {
   allowUnrelatedSetterType?: boolean;
   useGenericTypedArrays?: boolean;
   includeIterable?: boolean;
+  /** If true, treat async_sequence as AsyncIterable<T>, otherwise as any (legacy < TS 4.4 emit). */
+  treatAsyncSequence?: boolean;
 }
 
 export function emitWebIdl(
@@ -405,6 +407,17 @@ export function emitWebIdl(
     forReturn: boolean,
   ): string {
     function convertBaseType() {
+      // Support async_sequence (see https://github.com/whatwg/streams/pull/1372)
+      if (obj.type === "async_sequence") {
+        // AsyncIterable<T> requires separate asynciterable.d.ts until TS 6.0.
+        // To make it correct, we need to defer any functions using async_sequence to the asynciterable variant.
+        // For now, skip generation and warn.
+        console.warn(
+          "Skipping generation for a function or property with async_sequence type: " +
+            JSON.stringify(obj),
+        );
+        return "never"; // Use 'never' to signal omission in type generation
+      }
       if (obj.type === "sequence" && !forReturn && iterator !== "") {
         return "Iterable";
       }