[LUCENE-7800] Remove code that potentially rethrows checked exceptions from methods that don't declare them ("sneaky throw" hack)

• Type: Task
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 6.7, 7.0
• Lucene Fields: New
• Assignee: Dawid Weiss
• Reporter: Dawid Weiss
• Created: 22/Apr/17 18:47
• Updated: 28/Aug/22 15:14
• Resolved: 18/May/17 14:41

Description

For a long time I considered the "sneaky" throw hack to be a nice way of coding around some of Java's limitations (especially with invoking methods via reflection or method handles), but with time I started to see how it can be potentially dangerous and is nearly always confusing. If you have a Java method and its signature doesn't indicate the possibility of a checked exception you, as a programmer, simply don't expect it to happen. Never. So, for example, you could write:

try {
 luceneApi();
} catch (RuntimeException | Error e) {
  // Handle unchecked exceptions here.
}

and consider the code above to be absolutely bullet-proof in terms of handling exceptions. Unfortunately with sneaky throws anywhere in the "luceneApi" this is no longer the case – you can receive a checked exception that will simply fall through and hit some code frame above.

So I suggest we remove sneaky throw from the core entirely. It only exists in two places – private methods inside Snowball programs invoked via method handles (these don't even declare checked exceptions so I assume they can't occur) and AttributeFactory – here there is a real possibility somebody could declare an attribute class's constructor that does throw an unchecked exception. In that case I think it is more reasonable to wrap it in a RuntimeException than rethrow it as original.

Alternatively, we can modify the signature of createAttributeInstance and getStaticImplementation to declare some kind of checked exception (either a wrapper or even a Throwable), but I see little reason for it and it'd change the API.

Issue Links

• relates to: LUCENE-7796 Make reThrow idiom declare Error return type so callers may use it in a way that compiler knows subsequent code is unreachable