Captured Object.assign alias causes react-reconciler HostRoot render hang

[andrewtdiz]

Summary

Using latest npm Perry (@perryts/perry@0.5.1025) with React 19's reconciler, basic package import/root creation works, but the first real Fiber render hangs.

The smallest failing surface I found is react-reconciler HostRoot update processing:

const root = Renderer.createContainer(container, LegacyRoot, null, false, null, "id", onError, onError, onError, null);

Renderer.updateContainerSync(null, root, null, () => {});
Renderer.flushSyncWork(); // hangs under Perry

This reproduces even with null, so the failure is before host component creation, text nodes, function components, or mutation methods.

Versions

@perryts/perry@0.5.1025
react@19.2.6
react-reconciler@0.33.0
scheduler@0.27.0

The repro was bundled with esbuild to avoid CJS package loading noise.

Evidence

Instrumenting the bundled react-reconciler.production.js shows Perry reaches HostRoot and then throws inside processUpdateQueue:

trace: updateContainerSync.before
trace: updateContainerSync.after
trace: flushSyncWork.before
internal.performUnitOfWork.enter tag=3
internal.pushHostContainer.afterContextPush
internal.hostRoot.beforeCloneUpdateQueue
internal.hostRoot.afterCloneUpdateQueue
internal.processUpdateQueue.enter
internal.processUpdateQueue.loop tag=0 lane=2
internal.processUpdateQueue.case0 beforePayload payloadType=object
internal.processUpdateQueue.case0 beforeAssign assignType=number newStateType=object updateLaneType=object
internal.renderRootSync.catch value=[object Object] type=object then=undefined
internal.renderRootSync.catch value=[object Object] type=object then=undefined
...

The React reconciler code at that point is:

var assign = Object.assign;

// inside processUpdateQueue(...)
newState = assign({}, newState, update.payload);

Under Perry, that call throws, React catches the thrown object in renderRootSync, retries, and loops forever. If I patch just that call to direct Object.assign({}, newState, update.payload), Perry advances past HostRoot update processing and reaches renderer host calls like getChildHostContext, shouldSetTextContent, and createInstance.

Expected

Captured stdlib function aliases like this should remain callable and equivalent to the member call:

var assign = Object.assign;
assign({}, a, b);

React packages commonly capture stdlib members this way.

Guidance

Please investigate Perry's lowering/runtime representation for function-valued stdlib member references captured into locals, especially inside bundled CommonJS wrapper scopes. The failing bundle has multiple local assign = Object.assign bindings from React and react-reconciler; at the failing call site Perry reports the local alias as number and the call throws.

It would also help if thrown non-Error objects preserved enough diagnostic information to avoid this kind of silent retry loop. React's sync work loop keeps retrying because the thrown value is opaque ([object Object]) and not a thenable.

[andrewtdiz]

Taking a focused current-main cut for the captured Object.assign value shape.

Planned scope: keep Object.assign value reads on the reified Object constructor so const assign = Object.assign is a real function value (typeof, name, length) while preserving the existing alias-call rewrite and runtime copy semantics. I will add a node-suite object fixture for the React-style captured alias path.

Non-goals: broader React reconciler execution, unrelated Object.assign descriptor/proxy behavior, and general native-module callable alias work.

[andrewtdiz]

Opened draft PR #4270 for the captured Object.assign value-shape cut: #4270

Scope: value reads like const assign = Object.assign now stay on the reified Object constructor static so the captured value reports Node-shaped typeof, name, and length, while the existing alias-call rewrite and runtime copy semantics remain intact. The PR also corrects Object.assign.length to Node's value of 2 without changing the rest-argument thunk call arity.

Validation: Node 26 oracle, direct Perry-vs-Node output diff for the new fixture, focused node-suite/object/captured-object-assign, nearby assign-coercion-errors, cargo fmt --all -- --check, cargo check -p perry-hir -p perry-runtime, git diff --check, and file-size gate.

[andrewtdiz]

Current-main status update: PR #4270 merged on June 4, 2026 for the captured Object.assign value-shape issue.

Merged scope: const assign = Object.assign now reads a real function value from the reified Object constructor, with Node-shaped typeof, name, and length, while preserving existing alias-call rewrite/runtime copy semantics.

This issue looks stale-open unless the React reconciler HostRoot path has a newer blocker after the merged captured-alias fix.