setState in componentWillMount causes TypeError when rendering with renderToString and preceded by a component that renders with renderToString

[PKJedi]

Calling setState in componentWillMount of a component causes the error

TypeError: Cannot read property '_currentElement' of null
    at ReactCompositeComponentMixin._updateRenderedComponent

when rendering server-side with ReactDOMServer.renderToString and preceded by a component that renders content using ReactDOMServer.renderToString or ReactDOMServer.renderToStaticMarkup.

Causes TypeError with 0.14.8 and 15.0.0-rc.2:
https://github.com/PKJedi/react-dom-server-test/blob/master/test.js

Works with 0.13:
https://github.com/PKJedi/react-dom-server-test/blob/master/0.13/test.js

[gaearon]

Do we even support this? If we don't we should have a good early error message.

[Merri]

Yes, it is a supported feature according to the docs:

componentWillMount
Invoked once, both on the client and server, immediately before the initial rendering occurs. If you call setState within this method, render() will see the updated state and will be executed only once despite the state change.

Based on that the feature ought to work regardless of rendering method.

[aweary]

I've been looking at this issue this morning and it seems that it stems, at least partially, from the fact that ReactDefaultBatchingStrategy is being called when the first child component rendered has a call to renderToStaticMarkup or renderToString.

If you switch the order and render it second, then ReactServerBatchingStrategy (which is a noop) is used and the error isn't thrown.

If you remove the final

ReactUpdates.injection.injectBatchingStrategy(ReactDefaultBatchingStrategy);

from renderToStringImpl then the error isn't thrown, but that of course will have other implications.

[aweary]

So it looks like by the time enqueueUpdate is called, the batchingStrategy is already reset to ReactDefaultBatchingStrategy, even though the transaction that wrapped the ReactReconciler.mountComponent call was pulled from the ReactServerRenderingTransaction object pool.

Since ReactServerRenderingTransaction.batchedUpdates is a noop, and ReactDefaultBatchingStrategy.batchedUpdates is not, it's incorrectly attempting to apply the batched updates when it shouldn't.

[jimfb]

cc @spicyj

[aweary]

I still have a rather naive understanding of how ReactUpdates works, but would it be reasonable to just enqueue any injectBatchingStrategy calls when there is still a transaction that hasn't been released, instead of applying it immediately? That way any actions in transaction.perform would finish will the batching strategy they expected?

[sophiebits]

IIRC we don't support nested server rendering at the moment and have another issue about it somewhere.

[aweary]

@spicyj I opened a PR #7033 with a fix that resolves this issue, let me know what you think.