Summary

Repeatable annotations without an @Target annotation should be allowed to have a container annotation with an @Target that explicitly includes module declarations.

Problem

Repeatable annotations are required to be applicable to at least the same kinds of program elements as their containing annotation type (JLS 9.6.3), and annotations without an @Target are applicable to module declarations (JLS 9.6.4.1).

Repeatable annotations with a @Target that explicitly lists all default targets except for MODULE and whose container annotation do not have an @Target are currently erroneously accepted by javac, and should be rejected:

import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Target;

@interface TC {
  T[] value() default {};
}

@Target({
  ElementType.CONSTRUCTOR,
  ElementType.PARAMETER,
  ElementType.TYPE,
  ElementType.METHOD,
  ElementType.LOCAL_VARIABLE,
  ElementType.PACKAGE,
  ElementType.ANNOTATION_TYPE,
  ElementType.FIELD,
  ElementType.RECORD_COMPONENT,
})
@Repeatable(TC.class) // error: containing annotation type (TC) is applicable to more targets than repeatable annotation type (T)
@interface T {}

Repeatable annotations without an @Target whose container annotations explicitly targets modules are currently erroneously rejected, and should be accepted by javac:

import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Target;

@Target(ElementType.MODULE)
@interface TC {
  T[] value() default {};
}

@Repeatable(TC.class)
@interface T {}

Solution

The solution is to update javac to include module declarations in the set of default targets of repeatable annotations.

See also discussion in https://github.com/openjdk/jdk/pull/2303.

Specification

No changes to the specification are required, this behaviour is already specified by JLS 9.6.3 and 9.6.4.1.

The change to javac to reconcile it with the specification is in https://github.com/openjdk/jdk/pull/2412.