Are Filer's originating elements useful?

Question

I'm working on a Java program (Dagger) that uses the Java annotation processing API to generate code. When our program encounters an annotation in Foo.java, it generates Foo$$InjectAdapter.java. We use the Filer API to attach the originating Element that triggered the generated code.

The Filer docs say that this is intended to aid incremental builds:

"This information may be used in an incremental environment to determine the need to rerun processors or remove generated files. Non-incremental environments may ignore the originating element information."

Does anyone know of an incremental environment that use this information? Does javac or the Eclipse compiler use this information?

Answer 1

Does anyone know of an incremental environment that use this information?

Sorry, I don't.

Does javac or the Eclipse compiler use this information?

1. javac:

   javac's internal annotation processing environment uses the javax.annotation.processing.Filer implementation class com.sun.tools.javac.processing.JavacFiler. Here's the relevant code snippet from this class:

   public JavaFileObject createSourceFile(CharSequence paramCharSequence, 
                                          Element[] paramArrayOfElement) throws IOException {
       return createSourceOrClassFile(true, paramCharSequence.toString());
   }
   

   i.e. it simply throws away the originating element(s), not using it/them in any way.

   Same is done for createClassFile and createResourceFile.

   So that's a big no.

2. Eclipse compiler:

   In Eclipse, you enable java 6 -style annotation processing via

   Project properties -> Java Compiler -> Annotation Processing -> Check “Enable Project Specific Settings” & Check “Enable annotation processing”

   This delegates annotation processing to JDT-Core internal compiler, which uses it's own implementation of annotation processing. Eclipse 4.2, 3.7 and 3.6 source code does not contain the strings javax.annotation.processing or originatingElements - i.e. does not use the new java 6 annotation processing API at all. When searching for Filer, we see that it uses the old jdk-5 style Filer interface:

   org.eclipse.jdt.apt.core.internal.env.BuildFilerImpl extends org.eclipse.jdt.apt.core.internal.env.FilerImpl, which implements com.sun.mirror.apt.Filer

   All of these have method signatures:

   PrintWriter createSourceFile(String name) throws IOException;
   OutputStream createClassFile(String name) throws IOException;
   PrintWriter createTextFile(Location loc, String pkg, File relPath, String charsetName) throws IOException;
   OutputStream createBinaryFile(Location loc, String pkg, File relPath) throws IOException;
   

   So that's a big no.