`is null` and `is not null` can't be used in expression contexts

[jnm2]

Looking at https://github.com/AArnott/CSharpIsNull/blob/main/src/CSharpIsNullAnalyzer/CSIsNull001.cs and https://github.com/AArnott/CSharpIsNull/blob/main/src/CSharpIsNullAnalyzer/CSIsNull002.cs, I didn't see anything checking for this.

using System;
using System.Linq.Expressions;

// ❌ CS8122 An expression tree may not contain an 'is' pattern-matching operator.
//                                        ↓↓↓↓↓↓↓↓↓
_ = (Expression<Func<string, bool>>)(s => s is null);

// ❌ CS8122 An expression tree may not contain an 'is' pattern-matching operator.
//                                        ↓↓↓↓↓↓↓↓↓↓↓↓↓
_ = (Expression<Func<string, bool>>)(s => s is not null);

_ = (Expression<Func<string, bool>>)(s => s is object); // Works

(SharpLab)

[jnm2]

This is what I settled on to deal with recursive nesting properly: dotnet/roslyn#51446 (reply in thread)

[AArnott]

Interesting. Do you have time to send a PR with tests and a fix?

[jnm2]

Sorry, probably not soon.