feat(typing): use keyof inference to simplify definition

[HerringtonDarkholme]

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 (require new TS compiler)
• 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:

Our typing is very complex. This pull request uses the new feature from TS 2.7 to combine record style and array style prop definition into one. microsoft/TypeScript#19227
A simpler type definition should be beneficial to both our users and we maintainers.

Kudos to @sandersn @DanielRosenwasser !

Note: this requires TS 2.7+. So it is expected to be included in a minor version update.

[DanielRosenwasser]

@yyx990803, I haven't tried this yet, but I think the TypeScript template in vue-cli should have this in the box if possible.

[DanielRosenwasser]

Though, wait @HerringtonDarkholme, doesn't this mean that every type in props ends up being {}?

[HerringtonDarkholme]

@DanielRosenwasser @sandersn has a following fix to inferany.
microsoft/TypeScript#21271

[ktsn]

LGTM 😄

[yyx990803]

There's a flow error causing the TS test to be skipped. Can we rebase against latest dev to get CI passing?

[yyx990803]

@HerringtonDarkholme this PR seems to have been messed up by force pushes.

The type tests are failing after manual cherry-picking locally - can you take another look?

[HerringtonDarkholme]

It looks like TypeScript has added a new inference priority for literal type as in https://github.com/Microsoft/TypeScript/pull/22525/files.

This means keyof T will not picked up as inference if mapped type exists. In our case, PropsDefinition = ArrayProp | RecordProp is such situation. To work around this, we will still need a function call overload as we are doing now....

But it does not simplify our type definition.

[HerringtonDarkholme]

In short, we cannot achieve simpler definition in 2.6.

But we probably can rewrite the definition in Vue 3.0 with conditional types! I have used in my own project and it works quite well.

As for now, let's close this issue.