Replace `@Nonnull(when = When.MAYBE) ` by `@CheckForNull` in `@Nullable`

[xenoterracide]

it appears this is found in the findbugs jsr305 annotations my reason why is I want to enable -Werror and I'm using java modules module-info.java and it appears you can't use jsr305 as the automatic module name. sadly I don't actually know what When does or if there's a replacement. most tools seem to respect annotations named Nullable or NonNull now.

/home/xeno/.gradle/caches/modules-2/files-2.1/org.springframework/spring-core/5.3.8/da9b87dacaa5bbf80fad0f7b483988372a00a152/spring-core-5.3.8.jar(/org/springframework/lang/Nullable.class): warning: Cannot find annotation method 'when()' in type 'Nonnull': class file for javax.annotation.Nonnull not found
warning: unknown enum constant When.MAYBE
  reason: class file for javax.annotation.meta.When not found
error: warnings found and -Werror specified
1 error
2 warnings

❯ ./gradlew --version && ./gradlew :authn:dependencyInsight --configuration runtimeClasspath --dependency spring-core                                                                      # backend -> master + !

------------------------------------------------------------
Gradle 7.1.1
------------------------------------------------------------

Build time:   2021-07-02 12:16:43 UTC
Revision:     774525a055494e0ece39f522ac7ad17498ce032c

Kotlin:       1.4.31
Groovy:       3.0.7
Ant:          Apache Ant(TM) version 1.10.9 compiled on September 27 2020
JVM:          11.0.11 (AdoptOpenJDK 11.0.11+9)
OS:           Linux 5.10.42-1-MANJARO amd64

Type-safe dependency accessors is an incubating feature.
Type-safe project accessors is an incubating feature.

> Task :authn:dependencyInsight
org.springframework:spring-core:5.3.8

[serv-inc]

Does https://stackoverflow.com/questions/61140322/jetty-run-error-java-lang-typenotpresentexception-type-javax-annotation-meta-wh help ?

    <dependency>
        <groupId>com.google.code.findbugs</groupId>
        <artifactId>jsr305</artifactId>
        <version>3.0.2</version>
    </dependency>

[sbrannen]

Do you have jsr305-3.0.2.jar in the class path or module path?

it appears you can't use jsr305 as the automatic module name.

What happens when you attempt to do that?

Are you encountering issues with split packages?

[chirag-ji]

I've also getting this, but adding jsr305 worked.

I wonder why it is not working as it was available as a transitive dependency in the classpath, but working fine after adding it as 'direct dependency`. Any one please share some views on it.

[sdeleuze]

This is a known side effect of current JSR 305 support, the Java compiler generates warning on annotation with enum values when not present in the classpath while it is lenient for the annotations themselves. As suggested by Sam, the workaround is to have the jsr305 in the classpath or module path.

If I am not mistaken, this only occurs when user code is using Spring null-safety annotations, so that's on purpose that we don't add jsr305 to the transitive dependencies in a mandatory way.

The middle term fix will be to switch to https://github.com/jspecify/jspecify (where Spring team is involved) and remove those JSR305 annotations from Spring ones.

@sbrannen What about creating an issue dedicated to switching from JSR 305 to JSpecify in the 6.x Backlog in order to give visibility to our users and closing this one?

[sbrannen]

• Closing as superseded by Migrate to JSpecify annotations for nullability constraints #28797.

[cpovirk]

I am all in favor of a migration to JSpecify, but FYI, I suspect that you can prevent this warning by changing...

spring-framework/spring-core/src/main/java/org/springframework/lang/Nullable.java

Line 53 in 6f95af9

@Nonnull(when = When.MAYBE)

...to just...

@CheckForNull

We do this for a common annotation inside Google, and it works well with Kotlin.

[sdeleuze]

Thanks for the insight, I am going to give it a try.