Not tree shakable React Pure Component

[MariDani]

I am developping library of components with rollup and I am using agadoo tool to check if it is tree shakable.
Maybe this question is off the topic, but when I use the below code the library is not tree shakable. And I don't understand why.

import React from 'react';

class Welcome extends React.PureComponent {
    render() {
        return <h1>Hello, {this.props.name}</h1>;
    }
}

export default Welcome

On the other hand, when I don't use the React Component, it stays tree shakable, so what's wrong with the React component?

import React from 'react';

function Welcome(props) {
  return <h1>Hello, {props.name}</h1>;
}

export default Welcome

[steveluscher]

This is because agadoo can't know that the member expression React.PureComponent has no side effect.

Consider that React is an object. When you access a property of an object (in this case PureComponent) it might be backed by a ‘getter’ – a function that runs to get you the value.

const React = {
  get PureComponent() {
    // Perform some awful side effect.
    window.__PURE_COMPONENT_WAS_USED = true;
    return /* ... */;
  }
}

Agadoo just throws up its hands, says ‘I can't possibly know that property access didn't result in a side effect,’ and does not tree-shake the code away.