I am not in favor of more system properties to switch behavior all around. If sealed classes are of interest, then a Java 17 JVM is a reasonable requirement. I think this can be applied to records, switch expressions, etc. To keep it simple, require the minimum Java version that supports a feature natively. Releases are coming so fast now (every six months) that trying to backport this kind of thing to Java 11 or 8 seems less beneficial than it was a few years back.
From: Mario Garcia <mario.g...@gmail.com> Sent: Tuesday, September 21, 2021 3:10 AM To: dev@groovy.apache.org; Paul King <pa...@asert.com.au> Subject: [EXT] Re: [DISCUSS] Some potential additional system properties/CompilerConfiguration flags for Groovy 4 External Email: Use caution with links and attachments. Hi: Here are my thoughts. Maybe I'm wrong but, if somebody is familiar with JDK17 sealed classes, I don't think that person would expect that using sealed syntax with JDK8 is going to output a JDK17 sealed class. I would add it to the documentation and that's it. To me seems that implementing such scenario of compiler configuration is going to be done for the sake of part of the 1/3 of the potential users: * I would like to use sealed-classes -> use JDK17 * I love Groovy and I'd like to use sealed classes -> Use Groovy 4 and JDK 17 * I love Groovy but I'm stuck in JDK8 OR I love Java and I'd like to use sealed classes but again stuck in JDK8 -> Use Groovy 4 and be aware that, although it looks like sealed classes, you're not using JDK17, so it won't be the JDK17 sealed class Anyway, I would wait until this is really a real concern rather than a premature optimization and I would use that time and effort in other parts of the language. You already mentioned it, I also think Codenarc could be a good fit for this. My two cents El mar, 21 sept 2021 a las 9:41, Paul King (<pa...@asert.com.au<mailto:pa...@asert.com.au>>) escribió: Hi folks, [A bit of a long winded explanation but hopefully you will bear with me.] For recent features like sealed classes and records*, we are moving towards implementations which support the feature natively (as per Java) when compiled with a suitable target bytecode version, and fall back to some alternate mechanism on older JDK versions. E.g. native sealed classes vs a @Sealed annotation. For sealed classes there are flags in CompilerConfiguration (and corresponding system properties) to give better control, e.g. do you still want the annotations even on a native sealed class. Feedback on the existing implementation is as always welcome but that is distinct from what I am asking here. Do folks think an additional flag would be useful that failed compilation if the native option wasn't enabled? Here is an example to spell out the idea. The idea is that if I have: sealed class Shape { ... } final class Triangle extends Shape { ... } ... And then, if I compile with target bytecode at JDK17 I will get a sealed class (for Shape) as expected in the Java world but just one annotated with @Sealed if I use for instance JDK8. The target version is detected and used to switch between the two potential outcomes with already some flags to control the behavior a little. I wonder whether folks familiar with Java will be surprised that they use the `sealed` keyword but don't really get a sealed class and they are hoping to use the class as is with Java. It seems we have three options: (1) Leave as is. Our documentation explains the fallback scenarios, so users should familiarise themselves with it! (2) Provide an additional system property/flag/CompilerConfig setting which users could turn on and if the target bytecode version doesn't meet the required level for native support it would fail. The flag would be opt in, i.e. our existing best implementation based on version is the default but the flag would give a stricter option. With the flag set, if you compile my "sealed class" code on an old JDK it won't compile since I really meant to get a sealed class. (3) Leave this up to the next gen of CodeNarc Groovy 4 rules (not sure we have ever had version specific ones like this before). This example is around sealed classes but there will be similar concerns for records. Thoughts? * PR pending Cheers, Paul.
