fix #8721,#9873: wrong type when computed return about this

[yoyo930021]

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:
Fix vuejs/vetur#1707, vuejs/vetur#1509, #8721, #9873

When computed return about this property,
The this type is wrong.

[yoyo930021]

@ktsn I don't know this PR.
Is it the right solution?
I added the test about the question.
Please take a look.

[ktsn]

Looks good to me.

[Yahohoo]

@ktsn, aren't you going to merge this bugfix? You approved it in April but it's still not merged. This one affects Vetur and breaks intelisense so it seems quite important to me as VSCode + Vetur + Vue programmer.

[LHernZ]

Good evening, I'm wondering if someone forgot to merge this pull request, agree with @Yahohoo the intelisense is important for us, hoping someone merge it @ktsn or @yoyo930021

[VottusCode]

bump, @ktsn can you merge it?

[octref]

This does not seem to fix vuejs/vetur#1707
I'm testing with https://github.com/octref/veturpack. Manually writing the changes to node_modules/vue/types/options.d.ts doesn't fix the issue.

[yoyo930021]

This does not seem to fix vuejs/vetur#1707
I'm testing with https://github.com/octref/veturpack. Manually writing the changes to node_modules/vue/types/options.d.ts doesn't fix the issue.

vuejs/vetur#2131 (comment)

[octref]

@yoyo930021 Great, now we have TS 4.0.2 in Vetur by default as well. Are you planning to send a new PR to vue?

[yoyo930021]

@yoyo930021 Great, now we have TS 4.0.2 in Vetur by default as well. Are you planning to send a new PR to vue?

The problem is only work when typescript 3.9 up.
I don't know if we can accept this kind of PR?

[octref]

Updating devDependency should be fine...I guess? /cc @yyx990803

[yoyo930021]

I guess #11488 also can fix this problem.