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Infer Java @Nullable return types from Kotlin call sites

io.moderne.nullability.infer.InferJavaNullabilityFromKotlinCallSites

Adds the JSpecify @Nullable annotation to the return type of Java methods based on how those methods are used in Kotlin code. A Java method returning a reference type appears to Kotlin as a platform type (String!) of unknown nullability; Kotlin call sites that treat the result as possibly null reveal the intended contract. This recipe scans Kotlin sources for such usage — a safe call (call()?.x), an elvis operand (call() ?: fallback), a not-null assertion (call()!!), or a comparison to null — and writes @Nullable onto the matching Java method declaration, resolving the platform-type ambiguity. Only Java sources are modified; Kotlin sources are read for evidence and left unchanged. Conservative by design: it skips primitive and void returns, methods that already carry a nullability annotation, and @Override methods (where annotating the return could violate the supertype contract).

Recipe source​

This recipe is only available to users of Moderne.

This recipe is available under the Moderne Proprietary License.

Used by​

This recipe is used as part of the following composite recipes:

Example​

Unchanged​
import io.moderne.nullability.fixture.Greeter
fun use(g: Greeter): Int? {
    return g.getName()?.length
}
Before​
package io.moderne.nullability.fixture;

public class Greeter {
    public String getName() {
        return "x";
    }

    public String other() {
        return "y";
    }
}
After​
package io.moderne.nullability.fixture;

import org.jspecify.annotations.Nullable;

public class Greeter {
    @Nullable
    public String getName() {
        return "x";
    }

    public String other() {
        return "y";
    }
}

Usage​

This recipe has no required configuration options. Users of Moderne can run it via the Moderne CLI.

You will need to have configured the Moderne CLI on your machine before you can run the following command.

shell
mod run . --recipe InferJavaNullabilityFromKotlinCallSites

If the recipe is not available locally, then you can install it using:

mod config recipes jar install io.moderne.recipe:rewrite-nullability:0.1.0

See how this recipe works across multiple open-source repositories​

Run this recipe on OSS repos at scale with the Moderne SaaS.

The community edition of the Moderne platform enables you to easily run recipes across thousands of open-source repositories.

Please contact Moderne for more information about safely running the recipes on your own codebase in a private SaaS.

Data Tables​

Source files that had results​

org.openrewrite.table.SourcesFileResults

Source files that were modified by the recipe run.

Column NameDescription
Source path before the runThe source path of the file before the run. null when a source file was created during the run.
Source path after the runA recipe may modify the source path. This is the path after the run. null when a source file was deleted during the run.
Parent of the recipe that made changesIn a hierarchical recipe, the parent of the recipe that made a change. Empty if this is the root of a hierarchy or if the recipe is not hierarchical at all.
Recipe that made changesThe specific recipe that made a change.
Estimated time savingAn estimated effort that a developer to fix manually instead of using this recipe, in unit of seconds.
CycleThe recipe cycle in which the change was made.