Question about type annotations

Julian Bangert bangert at google.com
Tue Oct 18 21:34:58 UTC 2016 

Ok I hacked up something quick (see attachments). When running the tool, I
get
/usr/local/google/home/bangert/16/jdk-type-test/Annotation.java
/usr/local/google/home/bangert/16/jdk-type-test/Testcase.java
/usr/local/google/home/bangert/16/jdk-type-test/Generic.java
CompilationUnit:
/usr/local/google/home/bangert/16/jdk-type-test/Annotation.java
CompilationUnit:
/usr/local/google/home/bangert/16/jdk-type-test/Testcase.java


 MethodInvocation: super()
MethodSelect: JCTree.type: ()void
MethodSelect: Trees.type: ()void


 MethodInvocation: list.add(foo)
MethodSelect: JCTree.type: (@test.Annotation java.lang.String)boolean
MethodSelect: Trees.type: (java.lang.String)boolean


 MethodInvocation: Generic.<@Annotation() String>Method(foo)
MethodSelect: JCTree.type: (java.lang.String)void
MethodSelect: Trees.type: (java.lang.String)void
CompilationUnit:
/usr/local/google/home/bangert/16/jdk-type-test/Generic.java


 MethodInvocation: super()
MethodSelect: JCTree.type: ()void
MethodSelect: Trees.type: ()void


The trees API always strips metadata (which is unfortunate, but other parts
of error-prone already depend on JCType), so the annotations are always
gone. However, when looking at the JCTree.type field, the class method on a
generic has annotations on the substituted type parameter, whereas it
doesn't for the generic method call. The same applies to constructors.

Thanks again,
Julian
On Mon, Oct 17, 2016 at 6:00 PM Jonathan Gibbons <
jonathan.gibbons at oracle.com> wrote:

> A small program that parses the test case you already provided, to get an
> AST, then walks the AST, looking for selected nodes, printing out any
> relevant info.   Essentially, encapsulate this part of your message in
> demonstrable code:
>
>
> > Now call node.getMethodSelect() on the MethodInvocation AST nodes
> > generated by this snippet. For the first call site (list.add(foo)),
> > node.getMethodSelect() returns a JCFieldAccess with type
> >
> > "(@test.Annotation java.lang.String)boolean"
> <(@test.Annotationjava.lang.String)boolean> (note the annotation).
> >
> > When I do the same for Generic.<@Annotation String>Method, I merely get
> > "(java.lang.String)void".
>
>
> If (but only if) you're familiar with the javac code base, and more
> importantly, the test base, if you know of DPrinter, you might be able to
> use that to dump the AST.  In fact, something like
>     java -classpath ...  DPrinter.Main -after PARSE -showTreeTypes
> source-files...
>
> might get you pretty much all the way to a script you could post.
>
> -- Jon
>
>
>
> On 10/17/2016 05:46 PM, Julian Bangert wrote:
>
> Thanks for the quick response -- how would you prefer the stripped down
> example? Should I send an error-prone testcase?
>
> On Mon, Oct 17, 2016 at 5:38 PM Jonathan Gibbons <
> jonathan.gibbons at oracle.com> wrote:
>
> As is typically the case in requests like this, it would help if you
> could post a working, stripped down example.
>
> You're also working with javac internal objects. It would help if you
> could post an example in terms of the public API, such as is available
> using
>      com.sun.source.*
>      javax.lang.model.*
>
> For example, if you have identified a node in an AST by a TreePath, use
>      com.sun.source.util.Trees.getTypeMirror(TreePath)
> and then, since TypeMirror extends AnnotatedConstruct, you can get the
> annotation mirrors.
>
> See:
>
> http://download.java.net/java/jdk9/docs/jdk/api/javac/tree/com/sun/source/util/Trees.html
>
> http://download.java.net/java/jdk9/docs/api/javax/lang/model/type/TypeMirror.html
>
> http://download.java.net/java/jdk9/docs/api/javax/lang/model/AnnotatedConstruct.html
>
> -- Jon
>
> On 10/17/2016 05:18 PM, Julian Bangert wrote:
> > Hello (re-sending due to moderation),
> >
> > I am working on a checker based on the error-prone framework that
> > works with (Java 8) type annotations. The javac AST seems to be
> > missing annotation types for generic methods (and constructors on
> > generic types):
> >
> > // Annotation .java
> > package test;
> > import java.lang.annotation.ElementType;
> > import java.lang.annotation.Target;
> >
> >  @Target({
> >     ElementType.TYPE_USE,
> >     ElementType.FIELD,
> >     ElementType.LOCAL_VARIABLE,
> >     ElementType.PARAMETER,
> >     ElementType.METHOD
> >   })
> > public interface @Annotation {}
> >
> >
> > // Generic.java
> >  package test;
> >   public class Generic {
> >       public static <V> void Method(V value) {
> >       }
> >   }
> >
> > // Testcase.java
> >
> > package test;
> > import java.util.List;
> > public class Testcase {
> >     void test(List<@Annotation String> list, String foo) {
> >         list.add(foo);
> >         Generic.<@Annotation String>Method(foo);
> >     }
> > }
> >
> > Now call node.getMethodSelect() on the MethodInvocation AST nodes
> > generated by this snippet. For the first call site (list.add(foo)),
> > node.getMethodSelect() returns a JCFieldAccess with type
> >
> > "(@test.Annotation java.lang.String)boolean"
> <(@test.Annotationjava.lang.String)boolean> (note the annotation).
> >
> > When I do the same for Generic.<@Annotation String>Method, I merely get
> > "(java.lang.String)void".
> >
> > Is this a bug or intended behaviour? Is there a way to get annotation
> > on the types (besides implementing my own lookup, which might be
> > buggy/unelegant).
> >
> > Regards,
> > Julian
>
>
>
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