Implement(60881): Added detailed diagnostic for parent to child assignment #61145
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@microsoft-github-policy-service agree |
…0881 Syncing with upstream changes
…cMessages.json and changed it's code to 2881
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This newest change will fail the CI tests. However, it should correctly add the message we are looking for. I didn't accept the baseline so we can perform the difference checker in class tomorrow and ensure the new message is correct. |
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This PR doesn't have any linked issues. Please open an issue that references this PR. From there we can discuss and prioritise. |
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This PR contains a bunch of unrelated formatting changes which make this PR hard to review; you should revert these. If you have auto-format enabled in your editor, make sure it's running dprint. |
@jakebailey I've removed the formatting issues. Please let us know if there are any additional changes to be made. |
This reverts commit 8933230.
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@jakebailey Can you take another look at this issue? I think its ready for review. |
tests/baselines/reference/better_subType_assignable_to_superType_error_messsage.errors.txt
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| @@ -1,9 +1,9 @@ | |||
| conditionalTypes2.ts(15,5): error TS2322: Type 'Covariant<A>' is not assignable to type 'Covariant<B>'. | |||
| Type 'A' is not assignable to type 'B'. | |||
| 'B' could be instantiated with an arbitrary type which could be unrelated to 'A'. | |||
| 'B' is constrained to be a subtype of 'A'. | |||
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I'm not understanding why this error message is an improvement. What's the smallest example where this error is going to be easier to understand?
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@RyanCavanaugh This error message is an improvement because the original error message says that the two types could be unrelated but we know they are related in a parent child relationship, you just can't assign a parent to a child. We tried to pick a new error message that was similar to the suggestion in the original issue. This is the simplest example we looked at:
function example<SuperType, SubType extends SuperType>(superType: SuperType, subType: SubType) {
subType = superType;
}
Fixes #60881