fix provide isn't reactive with a single array, Fix #5223

[Kingwl]

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

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:
#5223

[HerringtonDarkholme]

Related: #5067

Would @znck please also give a look?

[znck]

One thing I don't want with provide/inject is child modifying ancestor's data.

If foo is injected & reactive then setting this.foo = null would set the provided prop to null. IMO that could be problematic.

Injected properties were kept non-reactive intentionally. Perhaps @yyx990803 could explain better.

[Kingwl]

https://facebook.github.io/react/docs/context.html#updating-context

React has an API to update context, but it is fundamentally broken and you should not use it.

should we warn when the context is changed？

[znck]

Currently, reactive objects can be provided.

https://jsfiddle.net/m0fyr6z1/3/ - In this example, you see, child re-renders if array is changed in parent component.

IMO, rather than setting provided injections (current implementation) or defining reactive injections (this PR), it would be better to add enumerable, non-configurable & read-only injections.

[znck]

/ping @yyx990803 – Your input required.

[yyx990803]

defineReactive accepts a fourth argument (customSetter) which allows overriding the default set behavior. We can just use that to do the warning when a child component attempts to mutate an injection binding. This is what we are doing for props too: https://github.com/vuejs/vue/blob/dev/src/core/instance/state.js#L71-L91

[yyx990803]

make sure to prefix warnings with process.env.NODE_ENV check :)

[Kingwl]

done

[rayrutjes]

Overriding the setter makes this PR introduce a BC.

[yyx990803]

It doesn't because it was not reactive anyway.

[rayrutjes]

In the project I'm working on, I did the following:

export default {
  inject: ['_searchStore'],
  props: {
    searchStore: {
      type: Object,
      default () {
        return this._searchStore
      }
    }
  }
}

Which will now break if I'm not mistaken.