Requested changes from review.

ChangeLog.md

@@ -19,6 +19,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fix analyzer [RCS0049](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS0049) ([PR](https://github.com/dotnet/roslynator/pull/1386))
 - Fix analyzer [RCS1159](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1159) ([PR](https://github.com/dotnet/roslynator/pull/1390))
+- Fix code fix for [CS8600](https://josefpihrt.github.io/docs/roslynator/fixes/CS8600) changing the wrong type when casts or `var` are involved ([PR](https://github.com/dotnet/roslynator/pull/1393))
 
 ## [4.10.0] - 2024-01-24
 

src/CodeFixes/CSharp/CodeFixes/DeclareAsNullableCodeFixProvider.cs

@@ -101,28 +101,31 @@ private static void TryRegisterCodeFixForCast(CodeFixContext context, Diagnostic
  async ct =>
  {
  NullableTypeSyntax newType = SyntaxFactory.NullableType(type.WithoutTrivia()).WithTriviaFrom(type);
- Document changedDocument = await context.Document.ReplaceNodeAsync(type, newType, ct).ConfigureAwait(false);
 
- // This could be in a variable declaration, so grab the new syntax root and find the newly-replaced type node
- SyntaxNode root = await changedDocument.GetSyntaxRootAsync(ct).ConfigureAwait(false);
- SyntaxNode insertedNewType = root.FindNode(type.Span);
-
- // Try finding a surrounding variable declaration whose type we also have to change
- if (insertedNewType.AncestorsAndSelf().FirstOrDefault(a => a.IsKind(SyntaxKind.EqualsValueClause)) is EqualsValueClauseSyntax equalsValueClause)
- {
- ExpressionSyntax expression = equalsValueClause.Value;
-
- if (equalsValueClause.IsParentKind(SyntaxKind.VariableDeclarator)
- && equalsValueClause.Parent.Parent is VariableDeclarationSyntax variableDeclaration
- && variableDeclaration.Variables.Count == 1
- && !variableDeclaration.Type.IsKind(SyntaxKind.NullableType)
- && variableDeclaration.Type is not IdentifierNameSyntax { Identifier.Text: "var" })
+ // This could be in a variable declaration whose type we also may have to change
+ if (type.Parent?.Parent is EqualsValueClauseSyntax
  {
- NullableTypeSyntax newDeclarationType = SyntaxFactory.NullableType(variableDeclaration.Type.WithoutTrivia()).WithTriviaFrom(variableDeclaration.Type);
- changedDocument = await changedDocument.ReplaceNodeAsync(variableDeclaration.Type, newDeclarationType, ct).ConfigureAwait(false);
+ Parent: VariableDeclaratorSyntax
+ {
+ Parent: VariableDeclarationSyntax
+ {
+ Variables.Count: 1,
+ Type: { IsVar: false } declarationType
+ } variableDeclaration
+ }
  }
+ && !declarationType.IsKind(SyntaxKind.NullableType))
+ {
+ NullableTypeSyntax newDeclarationType = SyntaxFactory.NullableType(declarationType.WithoutTrivia()).WithTriviaFrom(declarationType);
+ VariableDeclarationSyntax newVariableDeclaration = variableDeclaration
+ .ReplaceNode(type, newType)
+ .WithType(newDeclarationType);
+ return await context.Document.ReplaceNodeAsync(variableDeclaration, newVariableDeclaration, ct).ConfigureAwait(false);
+ }
+ else
+ {
+ return await context.Document.ReplaceNodeAsync(type, newType, ct).ConfigureAwait(false);
  }
- return changedDocument;
  },
  GetEquivalenceKey(diagnostic));