yield and Collection Expression Syntax

[TonyValenti]

There have been many requests for a yield all list;.
With collection expression syntax, an alternative syntax might be:
yield return ..list;

[HaloFour]

I don't think the syntax has ever been the problem as much as the behavior, the quadratic nature of nested iterators.

[colejohnson66]

For reference, see dotnet/roslyn#15 and #378