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Handle out-of-order binding of identifiers to improve tree-shaking #2803

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merged 1 commit into from Apr 10, 2019

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@lukastaegert lukastaegert commented Apr 10, 2019

This PR contains:

  • bugfix
  • feature
  • refactor
  • documentation
  • other

Are tests included?

  • yes (bugfixes and features will not be merged without tests)
  • no

Breaking Changes?

  • yes (breaking changes will not be merged unless absolutely necessary)
  • no

List any relevant issue numbers:
Resolves #2799

Description

It is possible that Rollup needs to analyze values of identifiers before they have been bound to their variables, which can cause in sub-optimal tree-shaking results. This is fixed here by allowing out-of-order binding of identifiers if their value is needed earlier. This allows for the following:

// input
export const test = () => {
	console.log(foo());
	console.log(bar());
};

const foo = () => {
	return BUILD ? A : B;
};

const bar = () => {
	return getBuild() ? A : B;
};

const getBuild = () => BUILD;

const BUILD = true;

// output
const test = () => {
	console.log(foo());
	console.log(bar());
};

const foo = () => {
	return A;
};

const bar = () => {
	return A;
};

export { test };
@lukastaegert lukastaegert merged commit c3d73ff into master Apr 10, 2019
5 of 6 checks passed
@lukastaegert lukastaegert deleted the gh-2799-improve-return-expression-evaluation branch Apr 10, 2019
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