SSR should check that instance belongs to Apollo before calling fetchData

[asmockler]

Intended outcome:

fetchData should not be called on components that do not belong to react-apollo during server render.

Actual outcome:

If the component is not expecting fetchData to be called, SSR will fail. Right now, when walking the tree, react-apollo only checks if an instance exists and that it has a function called fetchData:

react-apollo/src/getDataFromTree.ts

Lines 139 to 154 in 9222ab3

	walkTree(rootElement, rootContext, (element, instance, context) => {
	const skipRoot = !fetchRoot && element === rootElement;
	if (instance && typeof instance.fetchData === 'function' && !skipRoot) {
	const query = instance.fetchData();
	if (query) {
	queries.push({ query, element, context });
	// Tell walkTree to not recurse inside this component; we will
	// wait for the query to execute before attempting it.
	return false;
	}
	}
	});
	return queries;
	}

That is problematic if the instance has a function called fetchData that should not be called during server rendering.

How to reproduce the issue:

Add something along the lines of the following to a component being server rendered:

class MyComponent extends React.Component {
  fetchData() {
    throw new Error('fetchData should not be called');
  }

  render() { return null; }
}

Version

• [email protected]
• [email protected]

[benjamn]

The implementation of getDataFromTree has changed substantially in [email protected] (the latest version), thanks to #2533. In particular, we no longer attempt to detect whether component instances have a fetchData method. Please try updating, and feel free to reopen this issue if the problem persists.