What C# feature is this? - c#-9.0

Question

In my C# application (which uses C# 9) I had a line of code like this:
var filterCallback = new HitTestFilterCallback(
el => el is Path s && s.DataContext is IShape shp ?
HitTestFilterBehavior.Continue : HitTestFilterBehavior.ContinueSkipSelf);
Resharper suggested I "merge sequential checks". It rewrote the code to this
var filterCallback = new HitTestFilterCallback(
el => el is Path {DataContext: IShape shp}
?
HitTestFilterBehavior.Continue : HitTestFilterBehavior.ContinueSkipSelf);
I am interested in the bit that lets me write
{DataContext: IShape shp}
in place of
s.DataContext is IShape shp
Is there a specific technical language name for this feature? I want to read up on it to understand it better but I don't even know what to call it. I tried looking under "pattern matching" and reading about the "is" keyword but don't see anything that looks like it?

Answer 1

The feature is called "recursive patterns". In particular it is using a "property pattern" as part of a "recursive pattern".
You can find the proposal document here: https://github.com/dotnet/csharplang/blob/master/proposals/csharp-8.0/patterns.md
You can find a more informal blog post about it here: https://devblogs.microsoft.com/dotnet/do-more-with-patterns-in-c-8-0/