Do not include collection expression conversion to nullable value type in ClassifyStandardImplicitConversion() #74251
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…e in ClassifyStandardImplicitConversion()
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Do not include collection expression conversions to nullable value types in
ClassifyStandardImplicitConversion().User-defined conversions should not be considered in collection expression conversions. And it looks like the scenarios were not supported previously, even though
ClassifyStandardImplicitConversion()allowed user-defined conversions from nullable value types, becauseBinder.ConvertCollectionExpression()created aBoundCollectionExpressionwithHasErrors=truewhen the conversion was a user-defined conversion rather than a collection expression conversion.In some cases, such as the repro from #74185 with 17.8, a specific error was reported for the target type:
CS1061: 'Container<object>' does not contain a definition for 'Add'In other cases, no diagnostic was reported from binding, but the invalid
BoundCollectionExpressionwould cause emit to fail with a general error:CS7038: Failed to emit module: Unable to determine specific cause of the failure.Now, the user-defined conversion is ignored in
ClassifyStandardImplicitConversion(), and an error should be reported for the target type in all cases.Fixes #74185