Pre-deployment check on circular dependencies possible?

[vicary]

During a refactoring of our internal fork of this repo, we recently discovered the test util function doesNotBecomeCircular (linked below).

serverless-plugin-split-stacks/__tests__/migration-strategy/per-group-function.js

Lines 16 to 33 in 8164136

	const doesNotBecomeCircular = function (resources) {
	const memo = {};
	Object.keys(resources).forEach(resourceName => {
	const resource = resources[resourceName];
	if (resource.DependsOn) {
	resource.DependsOn.forEach(parent => {
	if (!memo[parent]) {
	memo[parent] = [resourceName];
	} else {
	memo[parent].push(resourceName);
	}
	});
	}
	});
	return Object.keys(memo).every(parentName => memo[parentName].length <= 1);
	};

We think this is a good starting point to detect potential errors before we wait for the long-running deployment process in CloudFormation, the situation gets significant for projects with more than 300 functions like ours. We have to wait for more than 1 hour just to discover this error.

This should also improve the situation in #20 #53 #83 #102 #105 #116 #122

@dougmoscrop Do you think this function is good enough as a pre-deployment assertion?

[dougmoscrop]

Oh wow, an hour! Yeah. I think I have some util code that also finds references via intrinsic functions not just dependsOn, which would add more cases to this early* detection

[vicary]

I am excited to see it happen!