core: look up custom gatherer relative to the config file path

[echopi]

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[echopi]

I signed it!

[googlebot]

CLAs look good, thanks!

[paulirish]

Thanks very much for the contribution! Appreciate it.
It's 7pm so we'll take a look tomorrow.

[patrickhulce]

awesome thanks for the addition @echopi! would you mind adding a test for your use case? ours are covered by the existing ones but we want to make sure not to break you in the future without a heads up :)

lighthouse/lighthouse-core/test/config/config-test.js

Lines 642 to 684 in ce8ed56

	it('loads a core gatherer', () => {
	const gatherer = loadGatherer('viewport-dimensions');
	assert.equal(gatherer.instance.name, 'ViewportDimensions');
	assert.equal(typeof gatherer.instance.beforePass, 'function');
	});
	it('loads gatherers from custom paths', () => {
	const customPath = path.resolve(__dirname, '../fixtures/valid-custom-gatherer');
	const gatherer = loadGatherer(customPath);
	assert.equal(gatherer.instance.name, 'CustomGatherer');
	assert.equal(typeof gatherer.instance.beforePass, 'function');
	});
	it('returns gatherer when gatherer class, not package-name string, is provided', () => {
	class TestGatherer extends Gatherer {}
	const gatherer = loadGatherer(TestGatherer);
	assert.equal(gatherer.instance.name, 'TestGatherer');
	assert.equal(typeof gatherer.instance.beforePass, 'function');
	});
	it('throws when a gatherer is not found', () => {
	assert.throws(_ => loadGatherer('/fake-non-existent-gatherer'), /locate gatherer/);
	});
	it('loads a gatherer from node_modules/', () => {
	// Use a lighthouse dep as a stand in for a module.
	assert.throws(_ => loadGatherer('mocha'), function(err) {
	// Should throw a gatherer validation error, but *not* a gatherer not found error.
	return !/locate gatherer/.test(err) && /beforePass\(\) method/.test(err);
	});
	});
	it('loads a gatherer relative to the working directory', () => {
	// Construct a gatherer URL relative to current working directory,
	// regardless of where test was started from.
	const absoluteGathererPath = path.resolve(__dirname, '../fixtures/valid-custom-gatherer');
	assert.doesNotThrow(_ => require.resolve(absoluteGathererPath));
	const relativeGathererPath = path.relative(process.cwd(), absoluteGathererPath);
	const gatherer = loadGatherer(relativeGathererPath);
	assert.equal(gatherer.instance.name, 'CustomGatherer');
	assert.equal(typeof gatherer.instance.beforePass, 'function');
	});

[echopi]

Done

[patrickhulce]

thanks @echopi! 👍 💯