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Improve indexed access type relations - #26698
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TypeScript Bot (@typescript-bot) test this |
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Heya Anders Hejlsberg (@ahejlsberg), I've started to run the extended test suite on this PR at d369cec. You can monitor the build here. It should now contribute to this PR's status checks. |
| return constraint && constraint !== errorType ? constraint : undefined; | ||
| const objectType = getConstraintOfType(type.objectType) || type.objectType; | ||
| if (objectType !== type.objectType) { | ||
| const constraint = getIndexedAccessType(objectType, type.indexType, /*accessNode*/ undefined, errorType); |
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Wouldn't this still result in a type we may need to get the constraint of if the constraint of tyoe.objectType is a generic mapped type (since an index on a mapped type is trivially bounded by the mapped type's template)? Or is getConstraintOfType not the variant that can do that?
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If the constraint of type.objectType is a mapped type, we do indeed fetch that here and form a new indexed access. If type.objectType itself is a mapped type, the getConstraintOfType function does nothing, and we'll fall into the base constraint code below.
| if (t.flags & TypeFlags.Substitution) { | ||
| return getBaseConstraint((<SubstitutionType>t).substitute); | ||
| } | ||
| if (isGenericMappedType(t)) { |
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This makes the constraint of a generic mapped type itself, right? I guess that makes sense since indexed accesses work that way already.
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Correct. I'm not sure why this code was here, but it definitely isn't right. Removing it had no effect on baselines (including RWC baselines), but it fixes the second issue I found while exploring #26409.
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Anders Hejlsberg (@ahejlsberg) This causes some good errors to disappear in the user tests. Mind taking a look? #26712 |
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Logged #26714 |
Fixes #26409.