Fix circular constraint check #25913
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When reviewing the baseline changes, note that the "disappearing" constraints are all in situations where a circularity error is also being reported. We now consistently remove constraints when they are circular. |
weswigham
reviewed
Jul 24, 2018
src/compiler/checker.ts
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| const bc = (<Type>target).immediateBaseConstraint; | ||
| return !!bc && bc !== circularConstraintType; | ||
| } | ||
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| return Debug.fail("Unhandled TypeSystemPropertyName " + propertyName); |
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While you're here revising this, it might be worth replacing Debug.fail( with Debug.asserNever(propertyName to guarantee exhaustiveness. Just a nit.
weswigham
approved these changes
Jul 24, 2018
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Looks good, but it might be worth commenting on getConstraintOfTypeParameter and/or getConstraintFromTypeParameter as to the nature of both and to which one you probably meant to use (similar to our comment on getContextualType that reads "Woah! Do you really want to use this function?").
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This PR ensures that we consistently call
getConstraintOfTypeParameterto obtain type parameter constraints. ThegetConstraintOfTypeParametermethod protects against circular constraints, unlike the lower levelgetConstraintFromTypeParameterhelper function.Fixes #25740.