C# detect primary constructor with Roslyn

Question

I'm trying to analyse the primary constructor of a class but I can't find how. It should be possible to find it in the syntax tree, I don't want to create the semantic model.

The code is pretty trivial.

string testCode = @"
public class TestClass(int someInt)
{

}";

var tree = CSharpSyntaxTree.ParseText(testCode);
var root = tree.GetRoot();
var cls = root.DescendantNodes().OfType<ClassDeclarationSyntax>().Single();
var primaryCtr = cls.DescendantNodes()
                    .OfType<PrimaryConstructorBaseTypeSyntax>()
                    .FirstOrDefault();

Console.WriteLine(primaryCtr != null ? "primaryCtr FOUND" : "NOT FOUND!");

This code outputs NOT FOUND! and I could not find any other way how to find it.

Miroslav · Accepted Answer · 2024-04-28 07:42:59Z

2

Let's see what the tree contains.

foreach (var item in root.DescendantNodes())
    Console.WriteLine(item.GetType().Name);

This outputs the following:

ClassDeclarationSyntax
ParameterListSyntax
ParameterSyntax
PredefinedTypeSyntax

That was little surprising but I guess it makes sense that in the parsed context the primary constructor is nothing else than a list of parameters.

So to detect the primary constructor I have to look for a ParameterListSyntax that is immediate descendant of the ClassDeclarationSyntax.

UPDATE

I found even a better way.

string testCode = @"
public class TestClass(int someInt)
{

}";

var tree = CSharpSyntaxTree.ParseText(testCode);
var root = tree.GetRoot();
var cls = root.DescendantNodes().OfType<ClassDeclarationSyntax>().Single();

if(cls.ParameterList == null)
    Console.WriteLine("NO PRIMARY CTR");
else
    Console.WriteLine("PRIMARY CTR FOUND");

edited Apr 28, 2024 at 7:42

answered Apr 28, 2024 at 7:32

Miroslav

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