Collection expression arguments: support [CollectionBuilder] factory methods #76998
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| Diagnostic(ErrorCode.WRN_NullabilityMismatchInTypeParameterNotNullConstraint, "[null]").WithArguments("MyCollectionBuilder.Create<T>(System.ReadOnlySpan<T>)", "T", "string?").WithLocation(7, 28), | ||
| //// (7,28): warning CS8714: The type 'string?' cannot be used as type parameter 'T' in the generic type or method 'MyCollectionBuilder.Create<T>(ReadOnlySpan<T>)'. Nullability of type argument 'string?' doesn't match 'notnull' constraint. | ||
| //// MyCollection<string?> x1 = [null]; // 1 | ||
| //Diagnostic(ErrorCode.WRN_NullabilityMismatchInTypeParameterNotNullConstraint, "[null]").WithArguments("MyCollectionBuilder.Create<T>(System.ReadOnlySpan<T>)", "T", "string?").WithLocation(7, 28), |
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This case was previously handled in Binder.GetAndValidateCollectionBuilderMethod() in the call to collectionBuilderMethod.CheckConstraints(). That was unintentional, because initial binding should check type constraints but not nullability constraints. Nullability constraints should be checked in NullableWalker, and the existing work item in #68786 covers that.
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Binding and lowering of collection expression arguments for target types that are constructed using
[CollectionBuilder]factory methods.See proposals/collection-expression-arguments.md