LibWeb: Add static method ReadableStream.from(any asyncIterable)

Tests/LibWeb/Text/expected/Streams/ReadableStream-from-asyncIterator.txt

@@ -0,0 +1,5 @@
+Well
+Hello
+Friends
+!
+🦬

Tests/LibWeb/Text/input/Streams/ReadableStream-from-asyncIterator.html

@@ -0,0 +1,30 @@
+<script src="../include.js"></script>
+<script>
+    async function* asyncGenerator() {
+        yield "Well";
+        yield "Hello";
+        yield "Friends";
+        yield "!";
+        yield "🦬";
+    }
+
+    async function readStream(stream) {
+        const reader = stream.getReader();
+        while (true) {
+            const { done, value } = await reader.read();
+            if (done)
+                break;
+            println(value);
+        }
+    }
+
+    test(async () => {
+        const asyncIterable = {
+            [Symbol.asyncIterator]: asyncGenerator,
+        };
+
+        const readableStream = ReadableStream.from(asyncIterable);
+
+        await readStream(readableStream);
+    });
+</script>

Userland/Libraries/LibWeb/Streams/ReadableStream.cpp

@@ -68,6 +68,13 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<ReadableStream>> ReadableStream::construct_
     return readable_stream;
 }
 
+// https://streams.spec.whatwg.org/#rs-from
+WebIDL::ExceptionOr<JS::NonnullGCPtr<ReadableStream>> ReadableStream::from(JS::VM& vm, JS::Value async_iterable)
+{
+    // 1. Return ? ReadableStreamFromIterable(asyncIterable).
+    return TRY(readable_stream_from_iterable(vm, async_iterable));
+}
+
 ReadableStream::ReadableStream(JS::Realm& realm)
     : PlatformObject(realm)
 {

Userland/Libraries/LibWeb/Streams/ReadableStream.h

@@ -70,6 +70,8 @@ class ReadableStream final : public Bindings::PlatformObject {
 
     static WebIDL::ExceptionOr<JS::NonnullGCPtr<ReadableStream>> construct_impl(JS::Realm&, Optional<JS::Handle<JS::Object>> const& underlying_source, QueuingStrategy const& = {});
 
+    static WebIDL::ExceptionOr<JS::NonnullGCPtr<ReadableStream>> from(JS::VM& vm, JS::Value async_iterable);
+
     virtual ~ReadableStream() override;
 
     bool locked() const;

Userland/Libraries/LibWeb/Streams/ReadableStream.idl

@@ -29,7 +29,7 @@ dictionary ReadableStreamGetReaderOptions {
 interface ReadableStream {
     constructor(optional object underlyingSource, optional QueuingStrategy strategy = {});
 
-    [FIXME] static ReadableStream from(any asyncIterable);
+    static ReadableStream from(any asyncIterable);
 
     readonly attribute boolean locked;