How do I get AttributeData from AttributeSyntax in Roslyn?

Question

Question as in the title.

From an object of type AttributeSyntax how can I get the related AttributeData representation in order to access the metadata?

Axiom

Answer 1

You need to find the ISymbol that the syntax is applied to, call GetAttributes(), and find the returned AttributeData for which ApplicationSyntaxReference matches your AttributeSyntax.

Jochbed

How do you get the ISymbol for attribute? – Blocker

@Andez: The semantic model should have APIs to get the symbol for the AttributeSyntax. You can use the Syntax Tree Explorer to see which node & which API. – Jochbed

Answer 2

@SLaks answer is correct. Here is some code to retrieve attributes from a AttributeListSyntax:

using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis;
using System.Collections.Generic;

static class Extensions
{
    public static IReadOnlyList<AttributeData> GetAttributes(this AttributeListSyntax attributes, Compilation compilation)
    {
        // Collect pertinent syntax trees from these attributes
        var acceptedTrees = new HashSet<SyntaxTree>();
        foreach (var attribute in attributes.Attributes)
            acceptedTrees.Add(attribute.SyntaxTree);

        var parentSymbol = attributes.Parent!.GetDeclaredSymbol(compilation)!;
        var parentAttributes = parentSymbol.GetAttributes();
        var ret = new List<AttributeData>();
        foreach (var attribute in parentAttributes)
        {
            if (acceptedTrees.Contains(attribute.ApplicationSyntaxReference!.SyntaxTree))
                ret.Add(attribute);
        }

        return ret;
    }

    public static ISymbol? GetDeclaredSymbol(this SyntaxNode node, Compilation compilation)
    {
        var model = compilation.GetSemanticModel(node.SyntaxTree);
        return model.GetDeclaredSymbol(node);
    }
}

Torey

This doesn't work for assembly-level symbols. For those, use Compilation.Assembly.GetAttributes(). – Eyeleteer