add support for nested java annotations

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Please add support for nested Java annotations. Here is my guess at what the syntax might be, using the JPA annotations for example:

import javax.persistence._

@Entity
class Test {
    @ManyToMany
    @JoinTable { val joinColumns = Array(@JoinColumn{val name = "a name"}) }
    var test: String = _
}

In this example, the nested annotation is in an array value, but they should also be supported as single values:
{{@MyAnnotation { val test = @MyOtherAnnotation }}}

Here is a related [http://article.gmane.org/gmane.comp.lang.scala/8768 mailing list thread]. This feature is very important for interoperating with Java libraries, and I don't know of any current workaround.

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Imported From: https://issues.scala-lang.org/browse/SI-294?orig=1
Reporter: Matt Hellige (hellige)

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Jan Kriesten (jkriesten) said:
Since this is getting up on me currently - is there a plan to support this (in the near future)?

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Andreas Joseph Krogh (andreak) said:
So, can someone confirm this going into a 2.7.x release?

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@lrytz said:
Replying to [comment:11 andreak]:

So, can someone confirm this going into a 2.7.x release?

unfortunately not, it's going to be in 2.8.x only.

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Andreas Joseph Krogh (andreak) said:
Any words on when 2.8-release will be out?

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@lrytz said:
fixed in r17925 / r18002

syntax is:

@OuterAnnot(nested = new NestedAnnot())

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Julian Eberius (julian.eberius) said:
Hi. To me it seems that a special case of nested Annotations is still not working. It happens when a Scala annotation (i.e. a StaticAnnotation) contains a Java annotation, which contains named arguments (any annotation with more than one "value" argument)

class NestedAnnotationTest {
        // all of these work
	@ComplexJavaAnnotation(nested= new NestedJavaAnnotation2(arg="test"))
	@ComplexScalaAnnotation1(arg1=42, arg2="test")
	@ComplexScalaAnnotation2(nested = new NestedJavaAnnotation1(23))
	// this one throws "too many arguments for constructor NestedJavaAnnotation2"
        @ComplexScalaAnnotation2(nested = new NestedJavaAnnotation2(arg="test"))
	val field:int = 3;
}

Of course, NestedJavaAnnotation2 just looks like this

public @interface NestedJavaAnnotation2 {
	public String arg();
}

I tried to implement the TargetedAnnotation from #1846, but for this I need to put complex java annotations inside a scala annotation.

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@lrytz said:
Hi,

nesting a java annotation inside a scala StaticAnnotation is not allowed (I'll have to improve the error message). The reason is that arguments to scala annotations are type checked just like any other code. So if you write

@ScalaAnnotation(new JavaAnnotation(arg1 = 1, arg2 = "two"))

you will get an error

"too many arguments for constructor JavaAnnotation"

which is correct; the java annotation class does not have such a constructor. The reason why it works for non-nested java annotations is that we "abuse" the constructor / named arguments syntax for creating java annotations, so we don't actually type check it as an ordinary constructor call in that case.

We can't do the same special case for nested java annotations because we would have to generate an incorrect tree.

Lukas

Replying to [comment:20 julian.eberius]:

Hi. To me it seems that a special case of nested Annotations is still not working. It happens when a Scala annotation (i.e. a StaticAnnotation) contains a Java annotation, which contains named arguments (any annotation with more than one "value" argument)
{code}
class NestedAnnotationTest {
// all of these work
@ComplexJavaAnnotation(nested= new NestedJavaAnnotation2(arg="test"))
@ComplexScalaAnnotation1(arg1=42, arg2="test")
@ComplexScalaAnnotation2(nested = new NestedJavaAnnotation1(23))
// this one throws "too many arguments for constructor NestedJavaAnnotation2"
@ComplexScalaAnnotation2(nested = new NestedJavaAnnotation2(arg="test"))
val field:int = 3;
}
}}
Of course, NestedJavaAnnotation2 just looks like this
{code}
public @interface NestedJavaAnnotation2 {
public String arg();
}
}}

I tried to implement the TargetedAnnotation from #1846, but for this I need to put complex java annotations inside a scala annotation.