How do I insert a statement into a block with normalized whitespace using Roslyn?

Question

I'm new to Roslyn. I'm writing a code fix provider that transforms foreach blocks that iterate through the results of a Select, e.g.

foreach (var item in new int[0].Select(i => i.ToString()))
{
    ...
}

to

foreach (int i in new int[0])
{
    var item = i.ToString();
    ...
}

To do this, I need to insert a statement at the beginning of the BlockSyntax inside the ForEachStatementSyntax that represents the foreach block. Here is my code for that:

var blockStatement = forEach.Statement as BlockSyntax;
if (blockStatement == null)
{
    return document;
}
forEach = forEach.WithStatement(
    blockStatment.WithStatements(
        blockStatement.Statements.Insert(0, selectorStatement));

Unfortunately, doing that results in the whitespace being off:

            foreach (int i in new int[0])
            {
var item = i.ToString();
                ...
            }

I Googled solutions for this. I came across this answer, which recommended using either Formatter.Format or SyntaxNode.NormalizeWhitespace.

• I can't use Formatter.Format because that takes a Workspace parameter, and it looks I don't have access to a Workspace per Roslyn: Current Workspace in Diagnostic with code fix project.

• I tried using NormalizeWhitespace() on the syntax root of the document, but that invasively formatted other code not related to the fix. I tried using it on just the ForEachStatementSyntax associated with the foreach block, and then calling syntaxRoot = syntaxRoot.ReplaceNode(oldForEach, newForEach), but that results in the entire foreach block not being properly indented.

  namespace ConsoleApp1
  {
      class Program
      {
          static void Main(string[] args)
          {
              var array = new int[0];
              int length = array.Length;
  
  foreach (int i in array)
  {
      string item = i.ToString();
  }        }
      }
  }
  

So is it possible to simply insert the statement with the correct indentation in the first place, without having to format other code?

Thanks.

Answer 1

You can add the Formatter Annotation to the nodes that you want the formatter to run on using WithAdditionalAnnotations

blockStatement.Statements.Insert(0, selectorStatement.WithAdditionalAnnotations(Formatter.Annotation))