v-for class with Symbol.iterator not working properly when return value is modified

[plehnen]

Version

2.6.0-beta.3

Reproduction link

https://jsfiddle.net/vx1ygurm/

Steps to reproduce

Iterate with v-for on a class with Symbol.iterator (which does something with the returning value). See jsfiddle!

What is expected?

since 2.6-beta1 it should support iterables in v-for (#8179) d40eb9c, (#8179)

I thought, great, let's try this with my footnote class and get rid of that verbose "getItems()" accessor and directly pass the class with a Symbol.iterator.

What is actually happening?

But as soon as the values which should be iterated are mutated before they are returned (e.g. sort), it shows the Vue warn:
"You may have an infinite update loop in a component render function."

And the iterator gets called over 100 times.

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Even worse, if you put this class in a vuex state. Then it complains that it cannot be mutated (even though I don't actually mutate it)

[yyx990803]

.sort is a mutating method, when you call it it mutates the original array instead of creating a copy.