fix #5997: refactor function registerRef

[javoski]

fix #5997 .
When registering ref, if refs[key] is an array and ref is already in refs[key], then do nothing.

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

[javoski]

It's seems that flow is a little weak to check array type, even codes below couldn't pass.

if (Array.isArray(refs[key])) {
  if (refs[key].indexOf(ref)) {
    refs[key].push(ref)
  }
}

So I added a suppress_comment option to .flowconfig.

[Kingwl]

please add the test case😁

[javoski]

Will do it soon wenlu.wang <notifications@github.com>于2017年7月6日 周四19:12写道：

…

please add the test case😁 — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#6039 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AFJGFKWvafjfMr3H6bJZVysZN2oAyy5Bks5sLMElgaJpZM4OPczR> .

[wuchuguang]

upgrade vue2.4.4
parent1
child ref="child"
loop child

parent1.$refs.child is ok
parent2.$refs.child is undefined