JDK-19 adds String::valueOf calls to string concatenation

[skyrising]

With openjdk/jdk@cfee451 extra String::valueOf calls are inserted for objects passed to makeConcatWithConstants. Quiltflower should remove these for better readability.

[thewindsofwinter]

Hi, I can probably write this up real quick. Let me know where I should look!

[jaskarth]

Hey, thanks! I'd recommend that you look here, and just before the return insert a loop that goes over the parameters array and call, and runs the existing removeStringValueOf method over each exprent, to remove the valueOf call.

[thewindsofwinter]

Understood! Shouldn't be too difficult a fix, definitely will get it done within a few hours once I get a bit of free time. Question: how should we run tests before committing? Is there code style that I'll need to follow/recommended linting? Should I squash commits (probably unnecessary, my guess is I'll get it in one). Let me know, thanks!

[thewindsofwinter]

Just added a loop in extractParameters, hopefully what you wanted (since the only other place those parameters come up via a call to extractParameters). Let me know if that's what you want! Also, out of curiosity how does this integrate into the overall code? It's a little hard for a newcomer to understand 😅

[jaskarth]

Hey! Generally the best way to run tests is to use gradle's test feature or to create a junit configuration in IntelliJ IDEA if you use that. I forgot to attach my class file, but here: TestStringConcatJ19.zip (Added as a zip because github doesn't like class files) You should add this to the testData/classes/custom directory, and then add the name of the class to the SingleClassesTest class. Now you can test out your changes when you run the test suite!

Also I totally get the code being a bit hard to get a grasp of at first, it's a lot of things to take in at once- But to summarize, this is the main method processing class. If you take a look at that class, you'll see that there are a lot of transformations that are run on the code, for example finding switch expressions, creating for and foreach loops, and more. The highlighted bit of code there handles resugaring string concat for Java 9+, as string concat in that version is done with invokedynamic instead of chained StringBuilder calls as it once was. The code that you're changing handles each invokedynamic instance seperately, so you are working with a single concatenation at a time in your change. Hope that cleared things up, if you have any more questions please feel free to ask! If it's more convenient, you can also find us on Discord, in #decompilers-general :)

[jaskarth]

Fixed by #153