CSharpRemoveUnusedVariableCodeFixProvider does not work with top-level statements

[AlekseyTs]

Start with top-level statement:

int abc = 123;

Use "Remove unused variable fix".
Observed:

System.ArgumentNullException : Value cannot be null.
Parameter name: statement
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitGlobalStatement(GlobalStatementSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.GlobalStatementSyntax.Accept[TResult](CSharpSyntaxVisitor`1 visitor)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.SyntaxNodeRemover.SyntaxRemover.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitListElement[TNode](TNode node)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitList[TNode](SyntaxList`1 list)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.VisitCompilationUnit(CompilationUnitSyntax node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.CompilationUnitSyntax.Accept[TResult](CSharpSyntaxVisitor`1 visitor)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxRewriter.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.SyntaxNodeRemover.SyntaxRemover.Visit(SyntaxNode node)
   at Microsoft.CodeAnalysis.CSharp.Syntax.SyntaxNodeRemover.RemoveNodes[TRoot](TRoot root,IEnumerable`1 nodes,SyntaxRemoveOptions options)
   at Microsoft.CodeAnalysis.CSharp.CSharpSyntaxNode.RemoveNodesCore(IEnumerable`1 nodes,SyntaxRemoveOptions options)
   at Microsoft.CodeAnalysis.SyntaxNodeExtensions.RemoveNode[TRoot](TRoot root,SyntaxNode node,SyntaxRemoveOptions options)
   at Microsoft.CodeAnalysis.Editing.SyntaxGenerator.RemoveNode(SyntaxNode root,SyntaxNode node,SyntaxRemoveOptions options)
   at Microsoft.CodeAnalysis.CSharp.CodeGeneration.CSharpSyntaxGenerator.RemoveNodeInternal(SyntaxNode root,SyntaxNode declaration,SyntaxRemoveOptions options)
   at Microsoft.CodeAnalysis.CSharp.CodeGeneration.CSharpSyntaxGenerator.<>c__DisplayClass198_0.<RemoveNode>b__0(SyntaxNode r)
   at Microsoft.CodeAnalysis.Editing.SyntaxGenerator.PreserveTrivia[TNode](TNode node,Func`2 nodeChanger)
   at Microsoft.CodeAnalysis.CSharp.CodeGeneration.CSharpSyntaxGenerator.Isolate(SyntaxNode declaration,Func`2 editor)
   at Microsoft.CodeAnalysis.CSharp.CodeGeneration.CSharpSyntaxGenerator.RemoveNode(SyntaxNode root,SyntaxNode node,SyntaxRemoveOptions options)
   at Microsoft.CodeAnalysis.Editing.SyntaxEditor.RemoveChange.Apply(SyntaxNode root,SyntaxGenerator generator)
   at Microsoft.CodeAnalysis.Editing.SyntaxEditor.GetChangedRoot()
   at async Microsoft.CodeAnalysis.CodeFixes.SyntaxEditorBasedCodeFixProvider.FixAllWithEditorAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.GetChangedSolutionAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.ComputeOperationsAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.CodeActions.CodeAction.GetPreviewOperationsAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Editor.Implementation.Suggestions.SuggestedAction.GetPreviewResultAsync(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Editor.Implementation.Suggestions.SuggestedActionWithNestedFlavors.<>c__DisplayClass11_0.<GetPreviewAsync>b__0(<Unknown Parameters>)
   at async Microsoft.CodeAnalysis.Extensions.IExtensionManagerExtensions.PerformFunctionAsync[T](<Unknown Parameters>)
   at Microsoft.VisualStudio.Telemetry.WindowsErrorReporting.WatsonReport.GetClrWatsonExceptionInfo(Exception exceptionObject)

Relates to #43563 (test plan for "top-level statements")

[AlekseyTs]

CC @sharwell

[CyrusNajmabadi]

I'm a little surprised by these issues. We should have had some amount of testing of these scenarios for the existing top-level-statements features (i.e. interactive). Is there something very different about the simple-program top-level statements, and interactive top-level statements?

[AlekseyTs]

No, difference for the syntax tree shape

[AlekseyTs]

Actually, that is not accurate, there is no locals and local functions in interactive, they are fields and methods. So, there is a difference in syntax shape

[jcouv]

I'll take a look to block or fix this today

[sharwell]

This was fixed by #44455. @jcouv Can you update the milestone for when this actually shipped?