How to determine if a variable is in scope in node syntax with Roslyn?

Question

I am new to Roslyn. I am wondering if there is a way to determine if a variable is in scope at some position in the semantic model. To give some information about what I'm doing, I am trying to convert blocks foreachthat iterate over the results Select, for example. kind of

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

to

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

Here is the relevant part of my code fix provider. I am currently hard-coded for an iteration variable item:

var ident = SyntaxFactory.Identifier("item");

Then I extract the Bodyselector SimpleLambdaExpressionSyntaxand (in the case above), replacing the parameter iwith item, to get item.ToString():

var paramTokens = from token in selectorBody.DescendantTokens()
                  where token.Text == selectorParam.Identifier.Text
                  select token;
selectorBody = selectorBody.ReplaceTokens(paramTokens, (_, __) => ident);

, , item foreach, . - SemanticModel/Symbol/etc. API-?

.

Answer 1

.

, (, , , )

    const string code = @"
    public class AClass{
        private int MyFld = 5;
        protected double MyProp{get;set;}
        public void AMethod(){
            string myVar = null;
            for (int myIterator=0; myIterator<10;myIterator++)
                foreach (string str in new int[0].Select(i => i.ToString())){ }
        }
        public void AnotherMethod()
        {
            string anotherVar = null;
        }
    }";

-

void Main()
{
    var tree = CSharpSyntaxTree.ParseText(code);
    var root = tree.GetRoot();

    var startNode = root
        .DescendantNodes()
        .OfType<SimpleLambdaExpressionSyntax>() // start at the Select() lambda
        .FirstOrDefault(); 

    FindSymbolDeclarationsInAncestors(startNode, "myVar").Dump(); // True
    FindSymbolDeclarationsInAncestors(startNode, "anotherVar").Dump(); // False

    CompilationLookUpSymbols(tree, startNode, "myVar").Dump(); // True
    CompilationLookUpSymbols(tree, startNode, "anotherVar").Dump(); // False
}

// You could manually traverse the ancestor nodes, and find the different DeclarationSyntax-es. 
// I may have missed some, like CatchDeclarationSyntax..
// Error-prone but more fun.
public bool FindSymbolDeclarationsInAncestors(CSharpSyntaxNode currentNode, string symbolToFind)
{
    return currentNode
        .Ancestors().SelectMany(a => a.ChildNodes()) // get direct siblings
        .SelectMany(node => // find different declarations
            (node as VariableDeclarationSyntax)?.Variables.Select(v => v.Identifier.ValueText)
            ?? (node as FieldDeclarationSyntax)?.Declaration?.Variables.Select(v => v.Identifier.ValueText)
            ?? (node as LocalDeclarationStatementSyntax)?.Declaration?.Variables.Select(v => v.Identifier.ValueText)
            ?? new[] {
                (node as PropertyDeclarationSyntax)?.Identifier.ValueText,
                (node as MethodDeclarationSyntax)?.Identifier.ValueText,
                (node as ClassDeclarationSyntax)?.Identifier.ValueText,
                })
        .Any(member => string.Equals(member, symbolToFind));
}

// Or use the SemanticModel from the CSharpCompilation.
// Possibly slower? Also, not as much fun as manually traversing trees.
public bool CompilationLookUpSymbols(SyntaxTree tree, CSharpSyntaxNode currentNode, string symbolToFind)
{
    var compilation = CSharpCompilation.Create("dummy", new[] { tree });
    var model = compilation.GetSemanticModel(tree);
    return model.LookupSymbols(currentNode.SpanStart, name: symbolToFind).Any();
}