Within 'setData' method computed variables are re-calculated, even if are not used in template

[lusarz]

Version

1.0.0-beta.10

Reproduction link

https://github.com/lusarz/vue-test-utils/commit/51cf7b5c10cd2010c26a21d7e9f2cca400faacd1

Steps to reproduce

Use wrapper.setData(...) method

What is expected?

Computed properties that are not truly used in template shouldn't be re-calculated.

By 'truly used' I mean variables that are not filtered out by v-if directive.

What is actually happening?

All computed properties are calculated. In some situations it cause Cannot read property ${property} of null kind of errors.

[LinusBorg]

By 'truly used' I mean variables that are not filtered out by v-if directive.

That's not how Vue works. This computed property will be re-evaluated independent of the usage in the render function.

This is not a bug in the test-utils, it's how Vue is designed to work.

[lusarz]

@LinusBorg
I have some doubts. Could you check here:
https://github.com/lusarz/vue/commit/9ef5946f082a5565efdd0d0794371f61bf0e73d9

Both tests pass. In second one, when <span v-if="a">{{ b }}</span> is evaluated to not be rendered, function that calculates b is not invoked.

[LinusBorg]

Can't take a look right now but reopened for someone else to check

[LinusBorg]

Edit: Quickly checked this with a fiddle: https://jsfiddle.net/tohdxapr/1/

Seems OP is right, sorry :/

[lusarz]

No problem. @LinusBorg I turned off cache for computed property in fiddle: https://jsfiddle.net/tohdxapr/2/

With cache it doesn't prove anything :)

[lusarz]

This issue seems to be related with watchers which are launched in setData -> update methods:

vue-test-utils/src/wrappers/vue-wrapper.js

Lines 15 to 17 in c095221

	this._watchers.forEach(watcher => {
	watcher.run()
	})

I noticed that watcher on computed property is run here, not sure where this watcher is initialized