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GeezerVison is showing github.com — Improve indexed access type relations by ahejlsberg · Pull Request #26698 · microsoft/TypeScript

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@ahejlsberg

@ahejlsberg Anders Hejlsberg (ahejlsberg) commented Aug 27, 2018

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Fixes #26409.

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Anders Hejlsberg (ahejlsberg) added 3 commits August 27, 2018 15:50
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Examine all constraints of indexed access types in relations
eeabd52
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Add tests
9f83958
@ahejlsberg
Accept new baselines
d369cec
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Anders Hejlsberg (ahejlsberg) requested review from Ryan Cavanaugh (RyanCavanaugh) and Wesley Wigham (weswigham) August 27, 2018 23:13
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Anders Hejlsberg (ahejlsberg) commented Aug 27, 2018

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TypeScript Bot (@typescript-bot) test this
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TypeScript Bot (typescript-bot) commented Aug 27, 2018 •
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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.
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weswigham
Wesley Wigham (weswigham) approved these changes Aug 27, 2018
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@weswigham Wesley Wigham (weswigham) left a comment •
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Looks good - I actually like this more than the existing index type constraint code by a bit - it much more clearly defines the hierarchy of constraints we check. Just some clarifying questions.

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Comment thread src/compiler/checker.ts
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);

@weswigham Wesley Wigham (weswigham) Aug 27, 2018

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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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@ahejlsberg Anders Hejlsberg (ahejlsberg) Aug 28, 2018

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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.

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Comment thread src/compiler/checker.ts
if (t.flags & TypeFlags.Substitution) {
return getBaseConstraint((<SubstitutionType>t).substitute);
}
if (isGenericMappedType(t)) {

@weswigham Wesley Wigham (weswigham) Aug 27, 2018

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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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@ahejlsberg Anders Hejlsberg (ahejlsberg) Aug 28, 2018

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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) merged commit bd40583 into master Aug 28, 2018
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Anders Hejlsberg (ahejlsberg) deleted the indexedAccessConstraints branch August 28, 2018 01:14
@ahejlsberg Anders Hejlsberg (ahejlsberg) mentioned this pull request Aug 28, 2018
Object values are not assignable when wrapped in a Partial #26266
Closed
@sandersn Nathan Shively-Sanders (sandersn) mentioned this pull request Aug 28, 2018
🤖 User test baselines have changed #26712
Closed
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Nathan Shively-Sanders (sandersn) commented Aug 28, 2018

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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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@RyanCavanaugh Ryan Cavanaugh (RyanCavanaugh) mentioned this pull request Aug 28, 2018
Regression - able to use union containing non-indexing type as index #26714
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Ryan Cavanaugh (RyanCavanaugh) commented Aug 28, 2018

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Logged #26714
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@ahejlsberg Anders Hejlsberg (ahejlsberg) mentioned this pull request Sep 20, 2018
Regression: something is wrong with type checking in dev.20180919 #27223
Closed
@mattmccutchen Matt McCutchen (mattmccutchen) mentioned this pull request Oct 14, 2018
Change in generic behavior between 3.0.1 and >=3.1.1 #27895
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@jakebailey Jake Bailey (jakebailey) mentioned this pull request Jun 30, 2023
Constraints which are generic mapped types should have a constraint of the same mapping over their generic's constraint #21249
Closed
@microsoft Microsoft (microsoft) locked as resolved and limited conversation to collaborators Oct 21, 2025
@typescript-bot TypeScript Bot (typescript-bot) assigned Anders Hejlsberg (ahejlsberg) Oct 21, 2025
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@weswigham Wesley Wigham (weswigham) weswigham approved these changes
@RyanCavanaugh Ryan Cavanaugh (RyanCavanaugh) Awaiting requested review from RyanCavanaugh

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@ahejlsberg Anders Hejlsberg (ahejlsberg)

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@ahejlsberg @typescript-bot @sandersn @RyanCavanaugh @weswigham
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