Relax nested class @ConstructorBinding requirement

[philwebb]

It's a bit clunky that @ConstructorBinding is needed on nested classes. I think if the outer class is constructor bound we should assume the inner one is also constructor bound.

/cc @sdeleuze

[sdeleuze]

Indeed, as discussed my use case is the following.

@ConfigurationProperties("blog")
@ConstructorBinding
data class BlogProperties(val title: String, val banner: Banner) {

	@ConstructorBinding
	data class Banner(val title: String?, val content: String)

}

It would be nice to be able to reduce it to:

@ConfigurationProperties("blog")
@ConstructorBinding
data class BlogProperties(val title: String, val banner: Banner) {

	data class Banner(val title: String?, val content: String)

}

This would also allow to just switch from @ConfigurationProperties to @ImmutableConfigurationProperties without having to use @ConstructorBinding at all:

@ImmutableConfigurationProperties("blog")
data class BlogProperties(val title: String, val banner: Banner) {

	data class Banner(val title: String?, val content: String)

}

If I decompile Kotlin code and do some cleanup, in Java it gives:

@ConfigurationProperties("blog")
@ConstructorBinding
public final class BlogProperties {

   private final String title;

   private final BlogProperties.Banner banner;

   public final String getTitle() {
      return this.title;
   }

   public final BlogProperties.Banner getBanner() {
      return this.banner;
   }

   public BlogProperties(String title, BlogProperties.Banner banner) {
      this.title = title;
      this.banner = banner;
   }

   @ConstructorBinding
   public static final class Banner {

      private final String title;

      private final String content;

      public final String getTitle() {
         return this.title;
      }

      public final String getContent() {
         return this.content;
      }

      public Banner(String title, String content) {
         this.title = title;
         this.content = content;
      }

   }

}

[sdeleuze]

Thanks for the quick improvement!

[philwebb]

@sdeleuze I never got around to actually testing it with Kotlin. Let me know if it doesn't work for some reason.