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POHow do I get the type of the expression in a MemberSelectTree from a javac plugin?
 

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  1. POHow do I get the type of the expression in a MemberSelectTree from a javac plugin?
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    <p>I am trying to write an annotation processor in the JSR 269 format which uses javac's Compiler Tree API to do some source code analysis. I am interested in member select expressions, such as method calls.</p> <p>I can easily get the name of the method (or field, etc.) being selected. But I want to know what type the member is being selected from, and I cannot seem to find a straightforward way to do this. <code>Trees.getTypeMirror</code> returns <code>null</code> for everything I try calling it on (and the Javadoc gives no hints).</p> <p>I suppose I could exhaustively analyze every kind of expression on the left side of the member select and determine the static type of the expression by recursive analysis: <code>NewClassTree</code>, <code>TypeCastTree</code>, <code>MethodInvocationTree</code>, <code>ArrayAccessTree</code>, and many others. But this seems like a lot of error-prone work, and clearly javac already knows the static type of the expression since it needs this information for many purposes. But how do I get access to this type information?</p> <p>What I have so far:</p> <pre><code>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&lt;? extends TypeElement&gt; annotations, RoundEnvironment roundEnv) { for (Element e : roundEnv.getRootElements()) { final Trees trees = Trees.instance(processingEnv); final TreePath root = trees.getPath(e); new TreePathScanner&lt;Void,Void&gt;() { 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; } } </code></pre> <p>and what it prints when run on some simple code making method calls:</p> <pre><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 </code></pre>
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    1. USJesse Glick
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    1. COThanks for that question, which really doubles as a great concise example for the Compiler Tree API. For the record, above `processingEnv` comes from an `init(ProcessingEnvironment)` method that should also be overridden. Oh, and JRockit 1.6.0_29 still shows "null".
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      1. POHow do I get the type of the expression in a MemberSelectTree from a javac plugin?
      1. USmgaert
    2. CONo need to override `AbstractProcessor.init` in most cases.
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      1. POHow do I get the type of the expression in a MemberSelectTree from a javac plugin?
      1. USJesse Glick
 

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