@babel/plugin-transform-react-constant-elements generates non-tree-shakeable output

[wereHamster]

Bug Report

In #7372 the plugin started marking the hoisted values as pure. However the way it does it has no effect if the original React tree is more than one level deep. Let me illustrate…

Consider the following input:

export function ReactComponent() {
  return <svg><path /></svg>
}

Will get transformed to this (you can test it on the babel repl):

var _ref =
/*#__PURE__*/
React.createElement("svg", null, React.createElement("path", null));

export function ReactComponent() {
  return _ref;
}

However such an annotation has no effect and the _ref is retained by all bundlers (rollup, webpack/terser). This is expected, that's how the /*#__PURE__*/ annotation works.

Here is an example how rollup does (or rather does not) tree-shake such a module

One solution would be to wrap the value in an IIFE, as suggested by the above linked comment:

var _ref =
/*#__PURE__*/ (() => 
React.createElement("svg", null, React.createElement("path", null)))();

• Babel version(s): 7.x

[babel-bot]

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