Add composition api's computed function support to vue/no-side-effects-in-computed-properties close #1393

[sapphi-red]

This PR adds support for composition api's computed function to vue/no-side-effects-in-computed-properties.
close #1393

With computed properties, this rule only warned about mutating this.
But since computed functions does not use this, I made it warn about mutating any variables which are not declared inside the computed function.

For example

const foo = ref(0)
const bar = computed(() => {
  foo.value = 3 // here it will be warned, since `foo` is not declared inside computed
  return foo.value + 3
})

const baz = computed(() => {
  const foobar = [3,5,6]
  return foobar.sort().map(v => v + foo.value) // here it will not be warned, since `foobar` is declared inside computed
})

Is this approach ok? Any other one is better?
If it is ok, should I change the behavior with computed properties to this one?

[ota-meshi]

I think it's better to report only the variables defined in the setup() function scope. There can be many false negatives, but I think there are many false positives in the current process.

e.g.

const myUtils = { ... } // My utilities
export default {
  setup(props) {
    const array = reactive([])
    const foo = computed(() => myUtils.reverse(array)) // OK Build an array in reverse order.
    const bar = computed(() => array.reverse()) // NG
    const baz = computed(() => myUtils.reverse(props.array)) // OK Build an array in reverse order.
    const qux = computed(() => props.array.reverse()) // NG
  }
}

[sapphi-red]

I think the problem only lies with the CallExpressions.
I changed the code to only report variables which are declared inside setup functions.
But maybe it is possible to report mutations that are not by CallExpressions even if it is declared outside.

const myUtils = {}

myUtils.reverse() // this is ok, since it is unknown whether it is destructive
myUtils = null // this is a mutation
myUtils.count++ // this is a mutation

[ota-meshi]

The main purpose of this rule is to prevent a reactive loop due to mutation. Therefore, I don't think variables that are unlikely to be reactive should be reported.
I think it is possible to add options to check for other mutations.

[sapphi-red]

I see. Thank you for answering!

[sapphi-red]

Thank you for reviewing! I fixed it.

[sapphi-red]

I think the problem only lies with the CallExpressions.
I changed the code to only report variables which are declared inside setup functions.
But maybe it is possible to report mutations that are not by CallExpressions even if it is declared outside.

const myUtils = {}

myUtils.reverse() // this is ok, since it is unknown whether it is destructive
myUtils = null // this is a mutation
myUtils.count++ // this is a mutation

[ota-meshi]

Sorry for late reply. Thank you for changing. LGTM!