ICSharpCode Decompiler get from TypeReferenceExpression to TypeDeclaration?

I'm using ICSharpCode.Decompiler.Ast.AstBuilder (which is used by SharpDevelop, NRefactory and ILSpy under the hood; has taken inspiration from there too) from code to build an abstract syntax tree from a .NET Common Intermediate Language assembly.

var assembly = AssemblyDefinition.ReadAssembly(assemblyPath);
var astBuilder = new AstBuilder(new DecompilerContext(assembly.MainModule));
astBuilder.AddAssembly(assembly);
// astBuilder.SyntaxTree ...

The syntax tree contains TypeReferenceExpressions whenever a line like Math.Abs() is there. How can I retrieve the TypeDeclaration of the referenced type when it also exists in the same syntax tree?

The closest I got is TypeReferenceExpression.Type.ToTypeReference().Resolve() but this is very heavy to orchestrate, and I already have (I suppose) all the information in the syntax tree. I also tried manual lookup by using namespaces an identifiers but I guess there should be a better way.

Solution

You can use SyntaxTree.GetTypes() to enumerate all decompiled types. Since that's rather heavy, I'd build up a reference-to-declaration lookup, e.g.:

var assembly = AssemblyDefinition.ReadAssembly(assemblyPath);
var astBuilder = new AstBuilder(new DecompilerContext(assembly.MainModule));

astBuilder.AddAssembly(assembly);

var ast = astBuilder.SyntaxTree;

var lookup = ast.GetTypes(true)
                .ToDictionary(d => (TypeReference)d.Annotation<TypeDefinition>());

You can then fetch the TypeReference from your TypeReferenceExpression and use it to find the type's declaration in the lookup:

TypeReferenceExpression e = /* ... */;
TypeDeclaration declaration;

if (lookup.TryGetValue(e.Type.Annotation<TypeReference>(), out declaration))
    Console.WriteLine(declaration.GetText());  // do whatever