Collection expressions: type inference from spread elements #69856
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| @@ -2675,6 +2675,135 @@ static void Main(string[] args) | |||
| Diagnostic(ErrorCode.ERR_CantInferMethTypeArgs, "F").WithArguments("Program.F<T>(System.Func<T[]>)").WithLocation(9, 17)); | |||
| } | |||
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| [Fact] | |||
| @@ -615,6 +615,10 @@ private void MakeExplicitParameterTypeInferences(Binder binder, BoundExpression | |||
| { | |||
| MakeCollectionExpressionTypeInferences(binder, (BoundUnconvertedCollectionExpression)argument, target, kind, ref useSiteInfo); | |||
| } | |||
| else if (argument.Kind == BoundKind.CollectionExpressionSpreadElement) | |||
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I find it super confusing that this parameter's name is argument when it seems like it might be any subexpression of an argument. Not for this PR to fix, though.
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| // https://github.com/dotnet/roslyn/issues/68786: Ignoring top-level nullability of enumeratorInfo.ElementType. | ||
| LowerBoundInference(TypeWithAnnotations.Create(enumeratorInfo.ElementType), target, ref useSiteInfo); |
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Why not use ElementTypeWithAnnotations?
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Seems like this could break something and cause us to not infer a type as nullable where we should. Please make sure to test something like:
M([..[default(string?)]]);
void M<T>(T[] arr);There was a problem hiding this comment.
Thanks, I hadn't noticed ElementTypeWithAnnotations previously.
I've added a couple of tests for inferring nullability but we are still not handling collection expressions in NullableWalker. If possible, I'd prefer to handle this when fixing #68786.
| dynamic x = new[] { 2, 3 }; | ||
| var y = F([..x]); | ||
| y.Report(includeType: true); | ||
| var z = F([1, ..x]); |
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nit: might be nice to show a case with multiple spread arguments. #Resolved
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Added to TypeInference_Spread_01.
| CompileAndVerify(new[] { source, s_collectionExtensions }, expectedOutput: "(System.Object[]) [1, 2, 3], "); | ||
| } | ||
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| // If we allow inference from a spread element _expression_ rather than simply |
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would def want to do this eventually. I feel like if we can make return [null] "just work" then return [..[null]] should also just work.
ghost
added this to the 
See Type inference:
Fixes #69706
Relates to test plan #66418