How to get expression type in MemberSelectTree from javac plugin?

Question

How to get expression type in MemberSelectTree from javac plugin?

I am trying to write an annotation processor in JSR 269 format that uses the javac compiler API to do some analysis of the source code. I'm interested in element selection expressions, such as method calls.

I can easily select the name of the method (or field, etc.). But I want to know what type the member is selected from, and I cannot find an easy way to do this. Trees.getTypeMirrorreturns nullfor everything that I am trying to call it (and Javadoc does not give any hints).

I suppose I can exhaustively analyze all the expressions on the left side select the item and determine the static type of expression by recursive analysis: NewClassTree, TypeCastTree, MethodInvocationTree, ArrayAccessTreeand many others. But this seems to work with an error, and it is obvious that javac already knows the static type of the expression, since it needs this information for many purposes. But how do I access this type of information?

What I still have:

import com.sun.source.tree.MemberSelectTree;
import com.sun.source.tree.MethodInvocationTree;
import com.sun.source.util.TreePath;
import com.sun.source.util.TreePathScanner;
import com.sun.source.util.Trees;
import java.util.Set;
import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.annotation.processing.SupportedSourceVersion;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.TypeElement;
@SupportedAnnotationTypes("*")
@SupportedSourceVersion(SourceVersion.RELEASE_6)
public class PublicProcessor extends AbstractProcessor {
    public @Override boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        for (Element e : roundEnv.getRootElements()) {
            final Trees trees = Trees.instance(processingEnv);
            final TreePath root = trees.getPath(e);
            new TreePathScanner<Void,Void>() {
                public @Override Void visitMethodInvocation(MethodInvocationTree node, Void p) {
                    System.err.println("visiting method invocation: " + node + " of kind: " + node.getMethodSelect().getKind());
                    TreePath expr = TreePath.getPath(root, node);
                    System.err.println("  of type: " + trees.getTypeMirror(expr));
                    return super.visitMethodInvocation(node, p);
                }
                public @Override Void visitMemberSelect(MemberSelectTree node, Void p) {
                    System.err.println("accessing member: " + node.getIdentifier());
                    System.err.println("  from: " + getCurrentPath().getCompilationUnit().getSourceFile().toUri());
                    TreePath expr = TreePath.getPath(root, node.getExpression());
                    System.err.println("  in expr: " + expr.getLeaf());
                    System.err.println("  of type: " + trees.getTypeMirror(expr));
                    return super.visitMemberSelect(node, p);
                }
            }.scan(root, null);
        }
        return true;
    }
}

and what it prints on startup on some simple calls to create code:

visiting method invocation: new Class().method() of kind: MEMBER_SELECT
  of type: null
accessing member: method
  from: .../Whatever.java
  in expr: new Class()
  of type: null