fix: #455

[38elements]

This is related to #455 and #582.

updated hook is called in vm._update() at 2.0.8.
https://raw.githubusercontent.com/vuejs/vue/v2.0.8/dist/vue.js

I read below lines.

https://github.com/vuejs/vue/blob/f43ce3a5d8f73e273f2d03c9d86ea5662cda481a/src/core/instance/lifecycle.js#L182-L190

https://github.com/vuejs/vue/blob/653aac2c57d15f0e93a2c1cc7e6fad156658df19/src/core/observer/watcher.js#L187-L202

https://github.com/vuejs/vue/blob/b7445a2b945dcded287601ace8e711ab5cf35ab5/src/core/observer/scheduler.js#L130-L151

https://github.com/vuejs/vue/blob/653aac2c57d15f0e93a2c1cc7e6fad156658df19/src/core/observer/scheduler.js#L35-L94

https://github.com/vuejs/vue/blob/b7445a2b945dcded287601ace8e711ab5cf35ab5/src/core/observer/scheduler.js#L96-L105

https://github.com/vuejs/vue/blob/f43ce3a5d8f73e273f2d03c9d86ea5662cda481a/src/core/instance/lifecycle.js#L315

[eddyerburgh]

This is a good solution, but I'm not sure we should keep it long term.

The recent changes to run watchers synchronously has caused lots of bugs.

I have a PR open that will add an async option to Vue, so we can set that to make rendering work synchronously—vuejs/vue#8240

I think the solution when we have the async option is to remove the code that sets watchers to sync, because there are too many bugs. Instead we should warn that users with Vue < 2.6 must either update Vue or use Vue.nextTick for updates to the DOM.

One question with this PR—I don't think child components will call update with this solution?

[38elements]

Thank you for reply.
sync option is useful.
Since sync option is different from the original behavior of Vue,
I think that it is better to remove sync option.
Since if sync option is removed, I think it is not necessary to resolve #455,
I will remove code which resolve #455 and keep code which resolve #582.

One question with this PR—I don't think child components will call update with this solution?

I think update method of child component is replaced at below line.
I will add test.

https://github.com/vuejs/vue-test-utils/pull/661/files#diff-81317be9320c4ebacbb2460e0f504e58R28

[38elements]

@eddyerburgh

One question with this PR—I don't think child components will call update with this solution?

Since this test passed, child components are updated.

[38elements]

I will remove code which resolve #455 and keep code which resolve #582 within 3 days.

[eddyerburgh]

I think this issue will be fixed in #586

[38elements]

Since this change will be unnecessary, I close this pull request.

[38elements]

@eddyerburgh

I am sorry.
I change my opinion.
I think sync mounting option is necessary and should not be removed.
sync mounting option is useful.

It is not problem that sync mounting option is different from the original behavior of Vue.
It should be explicitly described in document that sync mounting option is different from the original behavior of Vue.

If the async option is added to Vue@2.6, it is not added to Vue < 2.6.
In this case, It is inconvenient to run the same test by different Vue versions.
At Vue@2.6+, it is possible to use async option is false.
At Vue < 2.6, it is impossible to synchronously test .
Or The expression in the test will become different depending on the Vue version.
I think it is better to abstract the difference between async option and existing sync mounting option by sync mounting option.

[eddyerburgh]

Ok, can you reimplement your original code for update?

[38elements]

@eddyerburgh
Thank you for reply.
I send pull request #675.