await Task.WhenAny(new List<Task>()) should not Hang

[TonyValenti]

Description

Run this code:

await Task.WhenAny(new List<Task>())

And it will hang your process.

This is a highly undesirable default behavior. It is not obvious this will hang and there is no easy way to detect that this was the cause.

Other information

I recommend one of the following adjustments:
If using Task.WhenAny() on an empty list/enumerable/array:
A) Throw a Sequence contains no elements exception.
OR
B) Immediately return Task.CompletedTask or Task.FromResult(default(T))

I am OK with either, but I think that A is the best option.

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Issue Details

---

Description

Run this code:

await Task.WhenAny(new List<Task>())

And it will hang your process.

This is a highly undesirable default behavior. It is not obvious this will hang and there is no easy way to detect that this was the cause.

Other information

I recommend one of the following adjustments:
If using Task.WhenAny() on an empty list/enumerable/array:
A) Throw a Sequence contains no elements exception.
OR
B) Immediately return Task.CompletedTask or Task.FromResult(default(T))

I am OK with either, but I think that A is the best option.

Author:	TonyValenti
Assignees:	-
Labels:	area-System.Threading.Tasks, untriaged
Milestone:	-

[stephentoub]

This is a regression in .NET 6 caused by #38896. It throws an ArgumentException as expected on previous versions.

[TonyValenti]

@stephentoub Thanks!