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Scala 3 Java interop: method on base class called instead of method on derived class #17073
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christian-mibex
asked this question in
Compiler internals Q&A
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Not sure if it's a bug or to be expected. We ran into runtime issues after upgrading to Scala 3.
//> using scala 3 //> using repository "https://maven.atlassian.com/repository/public" //> using lib "com.atlassian.webhooks:atlassian-webhooks-api:6.1.6" //> using lib "com.atlassian.bitbucket.server:bitbucket-webhooks-api:7.14.0" import com.atlassian.bitbucket.webhook.WebhookScopeAdapter import com.atlassian.webhooks._ val createRequest = WebhookCreateRequest.builder .name("name") .url("url") .build() println("Runs with scala 2")
Basically the class hierarchy of WebhookCreateRequest looks like (simplified):
public class CreateRequest extends AbstractRequest { private CreateRequest(Builder builder) { super(builder); } public static Builder builder() { return new Builder();} public static class Builder extends AbstractRequest.AbstractBuilder<Builder> { protected Builder self() { return this; } public build() { return new CreateRequest(this);} } } public abstract class AbstractRequest { abstract static class AbstractBuilder<B extends AbstractBuilder<B>> { private String name; private String url; AbstractBuilder() {} protected abstract B self(); public B name(String value) { this.name = value; return this.self(); } public B url(String value) { this.url = value; return this.self(); } } }
Now the inner class AbstractBuilder is not public, and when the Scala compiler calls the method on it instead of CreateRequest an IllegalAccessException is called.
The bytecode output of Scala 2/ Java compilation
// 10: invokestatic #30 // Method .../WebhookCreateRequest.builder:()L.../WebhookCreateRequest$Builder;
// 13: ldc #32 // String name
// 15: invokevirtual #35 // Method .../WebhookCreateRequest$Builder.name:(Ljava/lang/String;)L.../AbstractWebhookRequest$AbstractBuilder;
// 18: checkcast #12 // class .../WebhookCreateRequest$Builder
// 21: ldc #37 // String url
// 23: invokevirtual #39 // Method .../WebhookCreateRequest$Builder.url:(Ljava/lang/String;)L.../AbstractWebhookRequest$AbstractBuilder;
Compared to Scala 3 (issue on last line)
// 10: invokestatic #34 // Method .../WebhookCreateRequest.builder:()L.../WebhookCreateRequest$Builder;
// 13: ldc #36 // String name
// 15: invokevirtual #39 // Method .../WebhookCreateRequest$Builder.name:(Ljava/lang/String;)L.../AbstractWebhookRequest$AbstractBuilder;
// 18: ldc #41 // String url
// 20: invokevirtual #43 // Method .../AbstractWebhookRequest$AbstractBuilder.url:(Ljava/lang/String;)L.../AbstractWebhookRequest$AbstractBuilder;
Is there a reason the second and all further chained builder calls (here the url()) call) are compiled to call the base class method?
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