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https://issues.apache.org/jira/browse/GROOVY-10855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17638431#comment-17638431
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Paul King commented on GROOVY-10855:
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Missing Retention and/or Target isn't necessarily an error in general.
Retention defaults to RetentionPolicy.CLASS. Target defaults to any declaration
except a type parameter declaration. Having said that, CLASS doesn't make sense
for annotation collectors which are replaced and not kept even at the class
level. But see historical info below.
Historically we had numerous annotations with retention set to RUNTIME. There
was the potential for tools to make use of that information, potentially
replacing the need for JavaBean BeanInfo classes in some circumstances or
allowing utility methods for BeanDescriptor and/or PropertyDescriptor style
processing. As far as we know, no such tools were written (or at least none
became popular). Over time we started switching back to SOURCE. We could
certainly consider dropping RUNTIME to at least CLASS which would eliminate the
potential for tools using runtime introspection or to SOURCE which would also
disallow ASM-style processing tools. That would be a breaking change, so a
version 5+ thing I would think.
There was also evolution that took place. @Immutable was originally not an
annotation collector.
So that Groovy could process class files compiled in earlier versions, we kept
RUNTIME for its retention. It also has deprecated annotation attributes which
are ignored. Any introspected class files with that annotation can still be
processed, though again we aren't necessarily aware of any tools or scripts
that do such processing. It's been quite some time since @Immutable was made a
meta-annotation, so perhaps we could release note that we no longer support
reading that annotation from class files with those old Groovy versions. We'd
need to do some testing. I have a vague re-collection that adding back in the
"backwards compatible reading of @Immutable" was only partly done to be nice
from a compatibility point of view - there were actually errors at the ASM
level (maybe? class mismatch errors?) if the annotation was found but didn't
match what the definition said.
> Meta-annotation retention policy and target
> -------------------------------------------
>
> Key: GROOVY-10855
> URL: https://issues.apache.org/jira/browse/GROOVY-10855
> Project: Groovy
> Issue Type: Bug
> Reporter: Eric Milles
> Priority: Minor
>
> Groovy collector annotations {{@Canonical}}, {{@Immutable}}, {{@RecordType}}
> and {{@CompileDynamic}} have missing or misleading {{Retention}} and
> {{Target}} metadata. _Note:_ there may be others...
> {{@Canonical}} and {{@CompileDynamic}}: missing {{Retention}} and {{Target}}
> {{@Immutable}} and {{@RecordType}}: {{RetentionPolicy}} is {{RUNTIME}} but
> should be {{SOURCE}} since meta-annotation is not retained.
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