Syntax Tree manipulation

[JustArion]

Hi how would I go about manipulating the syntax tree to add say:

local x = 42

to

local x = 42;

and vice-versa? Note the only addition was a redundant ;

I have tried

var tree = LuaSyntaxTree.ParseText("local x = 42");
var root = tree.GetRoot();
var newToken = SyntaxFactory.Token(SyntaxKind.SemicolonToken);
var lastToken = root.GetLastToken();

var updatedRoot = root.InsertTokensAfter(lastToken, [newToken]);

But the following stack trace is thrown

System.InvalidOperationException: The item specified is not the element of a list.
   at Loretta.CodeAnalysis.Lua.Syntax.SyntaxReplacer.TokenListEditor.VisitToken(SyntaxToken token)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.VisitLiteralExpression(LiteralExpressionSyntax node)
   at Loretta.CodeAnalysis.Lua.Syntax.LiteralExpressionSyntax.Accept[TResult](LuaSyntaxVisitor`1 visitor)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.Visit(SyntaxNode node)
   at Loretta.CodeAnalysis.Lua.Syntax.SyntaxReplacer.BaseListEditor.Visit(SyntaxNode node)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.VisitListElement[TNode](TNode node)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.VisitList[TNode](SeparatedSyntaxList`1 list)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.VisitEqualsValuesClause(EqualsValuesClauseSyntax node)
   at Loretta.CodeAnalysis.Lua.Syntax.EqualsValuesClauseSyntax.Accept[TResult](LuaSyntaxVisitor`1 visitor)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.Visit(SyntaxNode node)
   at Loretta.CodeAnalysis.Lua.Syntax.SyntaxReplacer.BaseListEditor.Visit(SyntaxNode node)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.VisitLocalVariableDeclarationStatement(LocalVariableDeclarationStatementSyntax node)
   at Loretta.CodeAnalysis.Lua.Syntax.LocalVariableDeclarationStatementSyntax.Accept[TResult](LuaSyntaxVisitor`1 visitor)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.Visit(SyntaxNode node)
   at Loretta.CodeAnalysis.Lua.Syntax.SyntaxReplacer.BaseListEditor.Visit(SyntaxNode node)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.VisitListElement[TNode](TNode node)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.VisitList[TNode](SyntaxList`1 list)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.VisitStatementList(StatementListSyntax node)
   at Loretta.CodeAnalysis.Lua.Syntax.StatementListSyntax.Accept[TResult](LuaSyntaxVisitor`1 visitor)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.Visit(SyntaxNode node)
   at Loretta.CodeAnalysis.Lua.Syntax.SyntaxReplacer.BaseListEditor.Visit(SyntaxNode node)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.VisitCompilationUnit(CompilationUnitSyntax node)
   at Loretta.CodeAnalysis.Lua.Syntax.CompilationUnitSyntax.Accept[TResult](LuaSyntaxVisitor`1 visitor)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxRewriter.Visit(SyntaxNode node)
   at Loretta.CodeAnalysis.Lua.Syntax.SyntaxReplacer.BaseListEditor.Visit(SyntaxNode node)
   at Loretta.CodeAnalysis.Lua.Syntax.SyntaxReplacer.InsertTokenInList(SyntaxNode root, SyntaxToken tokenInList, IEnumerable`1 newTokens, Boolean insertBefore)
   at Loretta.CodeAnalysis.Lua.LuaSyntaxNode.InsertTokensInListCore(SyntaxToken originalToken, IEnumerable`1 newTokens, Boolean insertBefore)
   at Loretta.CodeAnalysis.SyntaxNodeExtensions.InsertTokensAfter[TRoot](TRoot root, SyntaxToken tokenInList, IEnumerable`1 newTokens)

[GGG-KILLER]

You'd have to get the LocalVariableDeclarationStatement from the tree and then call either .Update or .WithSemicolon and then replace the original node in the tree with the one with the semicolon that's returned by the .Update/.WithSemicolon methods.

[JustArion]

Could you please show an example of this? The intent here is not to specifically add a semicolon but rather add another SyntaxToken, the semicolon is a generic example of this. Same for removing a token.

[GGG-KILLER]

Well, the thing is, you can only add a token if it's part of the node's structure, you can't just generically add any token you want.