Is it possible to get a SemanticModel from a project file instead of a DLL?

Question

I am creating a code extractor/inlining tool that will make it easier for me to share snippets of source code. It will ideally take a method that I provide, walk the method's syntax tree looking for references to methods/types in my other assemblies, and extract them all into a single block of code. This way, if I want to share an extension method I wrote that references other extensions that reference other extensions, I don't have to painstakingly compile it all into something I can copy and paste on the internet.

This article got me started:

https://joshvarty.com/learn-roslyn-now/

And below is what I have so far. I have an extension method called TrimWhiteSpace() in a GeneralUtilities class in the MyExtensions namespace. The below code successfully identifies this extension, but I also want access to the method's body so that I can walk the syntax tree there looking for other extensions. Because I am using the DLL directly, it won't have access to the body, so I need to generate a SemanticModel using the project instead. Using the project path doesn't appear to work.

public static void SemanticsTest()
{
    var tree = CSharpSyntaxTree.ParseText(@"using MyExtensions;
    namespace TestNamespace
    {
    public static class TestClass
    {
        public static void CallTrimWhiteSpace()
        {
            var x = "" some string  "".TrimWhiteSpace();
        }
    }
    }");

    var root = tree.GetRoot();

    var assemblyPath = MetadataReference.CreateFromFile(typeof(GeneralUtilities).Assembly.Location);

    var compilation = CSharpCompilation.Create("MyCompilation",
        syntaxTrees: new[] { tree }, references: new[] { assemblyPath });

    var model = compilation.GetSemanticModel(tree);

    var expression = root.DescendantNodes().OfType<InvocationExpressionSyntax>().FirstOrDefault();
    var symbol = model.GetSymbolInfo(expression);
}