GetIterator on a class declaration throws 'is not iterable' — INT32 ClassRef rejected by js_get_iterator's primitive guard (blocks Effect's yield* SomeTag) #6454

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1. proggeramlug commented on Jul 16, 2026

   

   proggeramlug

   on Jul 16, 2026

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   Summary

   yield* / for…of / destructuring / spread over a class declaration throws
   TypeError: is not iterable in Perry, where Node iterates it.

   This blocks Effect's most central idiom — yield* SomeTag, where the tag is a
   class:

   class HttpRouter extends Context.Tag("HttpRouter")<...>() {}
   const router = yield* HttpRouter        // GetIterator(HttpRouter) — a CLASS

   It is the remaining failure in the web.ts app of the effect-compiled-experiment
   repro (logger.ts, forking.ts, api.ts all pass byte-identical to node).

   Minimal repro (no Effect involved)

   const Proto: any = {
     [Symbol.iterator](this: any) { return [this.key, "second"][Symbol.iterator]() }
   }
   function makeTag(key: string): any {
     function TagClass() {}
     Object.setPrototypeOf(TagClass, Proto)
     ;(TagClass as any).key = key
     return TagClass
   }
   
   const RawTag: any = makeTag("raw-tag")
   function* gRaw(): any { return yield* RawTag }
   console.log([...gRaw()])              // node ["raw-tag","second"] | perry ["raw-tag","second"]  OK
   
   class DeclTag extends makeTag("decl-tag") {}
   function* gDecl(): any { return yield* (DeclTag as any) }
   console.log([...gDecl()])             // node ["decl-tag","second"] | perry TypeError: is not iterable

   yield* on the factory's plain function object works. yield* on a class
   declaration extending it does not.

   Per-construct matrix (class declaration receiver)

   construct	node	perry
   yield* DeclTag	["decl-tag","second"]	TypeError: is not iterable
   [...DeclTag]	["decl-tag","second"]	TypeError: value is not iterable
   for (const v of DeclTag)	["decl-tag","second"]	TypeError: is not iterable
   const [a,b] = DeclTag	["decl-tag","second"]	TypeError: is not iterable
   Array.from(DeclTag)	["decl-tag","second"]	[] (silently wrong, no throw)

   Root cause

   Perry lowers a class declaration to an INT32-tagged ClassRef
   (INT32_TAG \| class_id). js_get_iterator
   (crates/perry-runtime/src/symbol/iterator.rs) guards its generic
   [Symbol.iterator] lookup with:

   // A primitive number / boolean / null / undefined is not iterable...
   let jsv = JSValue::from_bits(val_f64.to_bits());
   if !jsv.is_pointer() && !jsv.is_any_string() {
       throw_value_not_iterable();
   }

   A ClassRef is not pointer-tagged, so it is misread as a primitive number and
   throws before the lookup at the bottom of the function — even though
   js_object_get_symbol_property already resolves class refs correctly
   (bits >> 48 == 0x7FFE → CLASS_STATIC_SYMBOLS → resolve_proto_chain_symbol
   → class_parent_closure, the last of which exists specifically for
   class Svc extends Context.Tag(id)<...>() {}, #36/#321).

   So the resolution machinery is present and correct; the value never reaches it.

   Confirmed in the emitted IR for web.ts — the operand is a bare constant:

   if.then.13:                                        ; generator state == 0
     %r43 = call double @js_get_iterator(double 0x7FFE000000000002)   ; INT32 2 = class_id 2

   6 of 709 js_get_iterator calls across the 311-module build pass a constant
   class ref (in HttpLayerRouter.ts and HttpApiBuilder.ts).

   Caveat worth recording

   INT32_TAG | 2 (the number 2) and a ClassRef with class_id == 2 are
   bit-identical; only is_class_id_registered distinguishes them. Any fix must
   therefore keep throwing when a class-ref-shaped value resolves no
   [Symbol.iterator], so for (const x of 37) {} remains a TypeError even when
   class id 37 happens to exist. A number colliding with a registered class id that
   does carry [Symbol.iterator] is inherently ambiguous under this
   representation — vanishingly rare, but it is a real property of the encoding.

   Secondary: error-message parity

   Perry's messages on this path do not match node's for any subject:

   subject	node	perry
   yield* undefined	undefined is not iterable (cannot read property Symbol(Symbol.iterator))	is not iterable
   yield* 2	number 2 is not iterable (cannot read property Symbol(Symbol.iterator))	is not iterable
   [...2]	2 is not iterable	value is not iterable

   crates/perry-runtime/src/collection_iter.rs::not_iterable_message already
   produces node's exact format and is reused by the Map/Set constructors; the
   symbol/iterator.rs + array/iterator.rs throwers predate it and emit bare or
   "value"-prefixed text. Worth routing them through it (it needs null/
   undefined cases added — node prints undefined and object null).
2. proggeramlug

   changed the title [-]effect: HttpLayerRouter 'TypeError: is not iterable' blocks Layer.launch (4th layer; #6449 clears the first three)[/-] [+]GetIterator on a class declaration throws 'is not iterable' — INT32 ClassRef rejected by js_get_iterator's primitive guard (blocks Effect's `yield* SomeTag`)[/+] on Jul 16, 2026
3. proggeramlug commented on Jul 16, 2026

   

   proggeramlug

   on Jul 16, 2026

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   Combined-build validation (PR #6460 + PR #6449 + PR #6459)

   On a build carrying all three fixes, the minimal-repro matrix is fully identical to node — yield*, spread, for…of, Array.from, and destructuring on a class declaration all behave like node, and every primitive still throws. The only remaining diffs on the probe are the error message wording for primitives (perry: bare is not iterable; node: 2 is not iterable etc.) — the secondary parity gap above.

   Effect app status on the combined build (effect-compiled-experiment):

   app	status
   logger.ts	✅ byte-identical to node
   forking.ts	✅ byte-identical to node
   api.ts	✅ byte-identical to node
   web.ts	❌ next layer — TypeError: value is not a function at startup

   Two intermediate walls resolved along the way:

   • The layer-5 Unsupported schema or overlapping types / cannot extend "BadArgument" with "BadArgument" seen on a fix(runtime): resolve [Symbol.iterator] on a class declaration (#6454) #6460-only build (no fix(hir): per-evaluation statics for class expressions with heritage (#6438) #6449) does not reproduce on the combined build — it was an artifact of the class-statics aliasing fix(hir): per-evaluation statics for class expressions with heritage (#6438) #6449 fixes, feeding Schema.extend the same _tag: Literal twice.
   • Layer 6 (value is not a function) is a new, later failure — being traced now; will get its own issue rather than piling onto this one.
4. proggeramlug

   added 2 commits that reference this issue on Jul 16, 2026

   fix(runtime): resolve `[Symbol.iterator]` on a class declaration (#6454…

   ...

   6243035

   fix(codegen): make FFI provenance part of the object cache entry (#6439…

   ...

   b4b47ba
5. proggeramlug commented on Jul 17, 2026

   

   proggeramlug

   on Jul 17, 2026

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   Fixed by #6460 (fix(runtime): resolve [Symbol.iterator] on a class declaration), merged to main. effect's yield* SomeTag and the HttpLayerRouter iteration path now work — web.ts (which routes through HttpLayerRouter) serves byte-identical to Node. Closing as resolved.
6. proggeramlug

   closed this as completedon Jul 17, 2026