Type-use annotation on var lambda parameter

[Tagir Valeev]

Hello again!

Thanks to Srikanth Sankaran from the Eclipse compiler project, I've got an
additional context about this problem.
Between Java 11 and Java 19, the specification was saying a slightly
different thing [1]:

> If the annotation appears before a void method declaration or a local
variable declaration that uses var (§14.4), then there is no closest type.

Since Java 20, it was changed:

> If the annotation appears before a void method declaration or a variable
declaration that uses var (§14.4, §15.27.1), then there is no closest type.

This specification problem was reported as JDK-8295807 by Dan Smith [3] and
fixed by Gavin Bierman, as the result of the earlier report by Chris Povirk
[4].
However, it looks like the javac implementation was never updated to
reflect this specification change. I've created an issue JDK-8371683 in
tools/javac [5].

With best regards,
Tagir Valeev

[1] https://docs.oracle.com/javase/specs/jls/se19/html/jls-9.html#jls-9.7.4
[2] https://docs.oracle.com/javase/specs/jls/se20/html/jls-9.html#jls-9.7.4
[3] https://bugs.openjdk.org/browse/JDK-8295807
[4] https://mail.openjdk.org/pipermail/compiler-dev/2022-October/020593.html
[5] https://bugs.openjdk.org/browse/JDK-8371683

On Mon, Nov 3, 2025 at 12:32 PM Tagir Valeev <amaembo at gmail.com> wrote:

> Hello!
>
> I stumbled on the following issue. Let's consider this Java file:
>
> package com.example;
>
> import java.lang.annotation.Retention;
> import java.lang.annotation.Target;
> import java.util.function.Function;
>
> import static java.lang.annotation.ElementType.TYPE_USE;
> import static java.lang.annotation.RetentionPolicy.RUNTIME;
>
> @Retention(value=RUNTIME)
> @Target(value={TYPE_USE})
> @interface Anno {
> }
> public class TestClass {
>     public static void main(String[] args) {
>         Function<Integer, String> f = (@Anno var val ) ->
> Integer.toHexString(val);
>         System.out.println(f.apply(10));
>     }
> }
>
> As you can see, there's a TYPE_USE annotation which is applied to the
> lambda parameter declared with 'var' keyword. If I understand JLS 9.7.4 [1]
> correctly, this should not be legal:
>
> > If the annotation appears before a void method declaration or a variable
> declaration that uses var (§14.4, §15.27.1), then there is no closest type.
> If the annotation's interface is deemed to apply only to the type which is
> closest to the annotation, a compile-time error occurs.
>
> However, javac accepts this code. I tried different versions between Java
> 11 and Java 25, and the result is the same: the file is compiled
> successfully. However, the TestClass.class file contains no references to
> the Anno annotation at all, despite it having the RUNTIME retention. So it
> looks like the annotation is silently ignored.
>
> One thing that confuses me is that the Eclipse compiler (ecj-4.34.jar)
> also accepts this code. However, it generates
> a RuntimeVisibleTypeAnnotations attribute for the Anno annotation. So
> either both compilers accept this code incorrectly, or my understanding of
> the specification is wrong.
>
> Could you please take a look at the javac issue? I'd be happy to be
> corrected if I misunderstood the specification. Thank you in advance!
>
> Tagir Valeev
>
> [1]
> https://docs.oracle.com/javase/specs/jls/se25/html/jls-9.html#jls-9.7.4
>
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