Address bootstrapping issue

src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs

@@ -146808,5 +146808,32 @@ void M(T initial, System.Func<T, T?> selector)
  var comp = CreateCompilation(src);
  comp.VerifyDiagnostics();
  }
+
+ [Theory, WorkItem(52925, "https://github.com/dotnet/roslyn/issues/52925")]
+ [InlineData("")]
+ [InlineData(" where T : notnull")]
+ [InlineData(" where T : class")]
+ [InlineData(" where T : class?")]
+ public void VarDeclarationWithGenericType_RefValue(string constraint)
+ {
+ var src = $@"
+#nullable enable
+
+class C<T> {constraint}
+{{
+ ref T Passthrough(ref T value)
+ {{
+ ref var value2 = ref value;
+ return ref value2;
+ }}
+}}
+";
+ var comp = CreateCompilation(src);
+ comp.VerifyDiagnostics(
+ // (9,20): warning CS8619: Nullability of reference types in value of type 'T?' doesn't match target type 'T'.
+ // return ref value2;
+ Diagnostic(ErrorCode.WRN_NullabilityMismatchInAssignment, "value2").WithArguments("T?", "T").WithLocation(9, 20)
+ );
+ }
  }
 }

src/Dependencies/Collections/SegmentedDictionary`2.cs

@@ -442,7 +442,7 @@ private ref TValue FindValue(TKey key)
 ConcurrentOperation:
  ThrowHelper.ThrowInvalidOperationException_ConcurrentOperationsNotSupported();
 ReturnFound:
- ref var value = ref entry._value;
+ ref TValue value = ref entry._value;
 Return:
  return ref value;
 ReturnNotFound: