Debug assertion failure in GuardedAddBoundTreeForStandaloneSyntax

[sharwell]

Version Used:

Steps to Reproduce:

While debugging Roslyn with an open instance of Compilers.slnf, I observed the following assertion fail:

roslyn/src/Compilers/CSharp/Portable/Compilation/MemberSemanticModel.cs

Lines 1510 to 1514 in fa64d90

	Debug.Assert((manager is null && (!IsNullableAnalysisEnabled() || syntax != Root || syntax is TypeSyntax ||
	// Supporting attributes is tracked by
	// https://github.com/dotnet/roslyn/issues/36066
	this is AttributeSemanticModel)) ||
	(manager is object && remappedSymbols is object && syntax == Root && IsNullableAnalysisEnabled() && _lazySnapshotManager is null));

It's happening in the evaluation of Binder.DoUncheckedConversion in a speculative semantic model, and appears to impact code where the entire block body of a method is wrapped in unchecked { }. The manager is non-null, but the syntax != Root. Perhaps the assertion should be changed to syntax == GetBindableSyntaxNode(Root)?