Commits on Jul 6, 2022

1. Scala 2.13: Fix weaker access privileges error …

   Compiling under Scala 2.13, we see two identical compilation
   errors for traits `RssAtomModule` & `GModule`, which both
   extend the `com.sun.syndication.feed.module.Module` interface from
   ROME (used for processing RSS). The message is of the form:
   
   > weaker access privileges in overriding def clone(): Object (defined in trait Module)
   > override should be public;
   > (note that def clone(): Object (defined in trait Module) is abstract, and is therefore
   > overridden by concrete protected[package lang] def clone(): Object (defined in class Object))
   
   `com.sun.syndication.feed.module.Module` is a Java interface that specifies
   `clone()` should be *public*:
   
   ```
   public Object clone() throws CloneNotSupportedException;
   ```
   
   ...but it's just an interface, not a class - and so the `java.lang.Object.clone()` method,
   which is assigned `protected` as an access modifier, is more protected than the interface
   dictates - but it's the only `clone()` method available on our _trait_, whether that's
   `RssAtomModule` or `GModule`.
   
   This is a horrible little problem and various people have encountered it over the years:
   
   * scala/bug#3946
   * https://bugs.openjdk.org/browse/JDK-6946211
   
   How to fix?
   -----------
   
   There is a fairly good suggestion at https://stackoverflow.com/a/8619704/438886 - just
   define a concrete `clone()` method in the trait, with a guard implmentation that just
   throws `CloneNotSupportedException` - your concrete subclasses can override the method
   with whatever implementation they like. It's a bit of a hack, but it works.
   
   However, looking at the code of these two traits and their solitary implementations:
   
   * `RssAtomModule` with its implementation `RssAtomModuleImpl`
   * `GModule` with `GModuleImpl`
   
   ...there's no reason to separate the functionality here into a separate trait and class.
   It's not being used to facilitate testing, and each trait has only a single implementation.
   Sometimes a trait can be a nice way to decide exactly what limited public API you want
   people to think about when they use your code, but I don't think that's the case here.
   Totally fine to just unite each trait & class into a simple class, reducing unnecessary
   boilerplate, and removing the need to have a dummy `public` clone method!
   
   The compilation errors in full:
   
   ```
   [error] /Users/roberto/guardian/frontend/common/app/common/ShowcaseRSSModules.scala:16:7: weaker access privileges in overriding
   [error] def clone(): Object (defined in trait Module)
   [error]   override should be public;
   [error]   (note that def clone(): Object (defined in trait Module) is abstract,
   [error]   and is therefore overridden by concrete protected[package lang] def clone(): Object (defined in class Object))
   [error] trait RssAtomModule extends com.sun.syndication.feed.module.Module with Serializable with Cloneable {
   [error]       ^
   [error] /Users/roberto/guardian/frontend/common/app/common/ShowcaseRSSModules.scala:52:7: weaker access privileges in overriding
   [error] def clone(): Object (defined in trait Module)
   [error]   override should be public;
   [error]   (note that def clone(): Object (defined in trait Module) is abstract,
   [error]   and is therefore overridden by concrete protected[package lang] def clone(): Object (defined in class Object))
   [error] trait GModule extends com.sun.syndication.feed.module.Module with Serializable with Cloneable {
   [error]       ^
   ```

   

   rtyley committed Jul 6, 2022
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