remove an edge when there's cycles

[matthewmueller]

Okay I wanted to offer a solution. I haven't thought about all the possibilities here, but I think this would work.

Basically grab all the cycles, and remove the edge that completes the cycle, before doing the topological sort.

I've tested this on an app with cyclical dependencies and it seems to work fine. Unfortunately there are other parts of mako that throw with cycles, so they'll need to be updated too.

[dominicbarnes]

This function should not be manipulating the graph, we need to find a better solution. I checked out the implementation in graph.js, but they throw errors for cycles too.

We'll just need to add some tests and find a solution for this, I can work on it tonight.

[dominicbarnes]

Oh hahahah, that's a clone of the graph we are working on, so manipulating it is fine. Sorry about that @matthewmueller!

[dominicbarnes]

This solves #1

[matthewmueller]

sweet, glad we're on the same page that this (unfortunately) needs to get sorted out.

i think the only other piece is updating mako-tree to internally handle it for method calls like .removeFile, which throw if there are cycles. I'll get something working with the app I'm testing it on and then open a PR with some changes.

[dominicbarnes]

It looks like the changes made in this PR have negative consequences after all. I'm working on adding a cycle test in mako-js, and with a case like this: (borrowed from here)

index: a, b
a: b
b: a

This lib returns an empty array for the toposort, which means mako stops doing processing altogether. It looks like I'm going to need to find a proper toposort algorithm to port for handling cycles.