Support for standard library polyfills

[lqc]

I really like the idea behind this project. What the frontpage does not mention, is that a valid Java 8 bytecode can't still have a hard time running on actual JRE8 because of missing pieces of the standard library like List.of().

So the idea is that the plugin could somehow rewrite references of java.util.List#of() to a different static method in a specially created polyfill library.

What do you think?

[bsideup]

Hi @lqc,

Jabel does not backport the stdlib, only the syntax.

It would be a completely different scope (and some libraries have attempted to do so, e.g. https://github.com/JavaMoney/jsr354-api-bp), and I do not consider doing it right now given the much bigger complexity

[bsideup]

It also worth mentioning that the language features enabled by Jabel do not require any new stdlib methods btw

[lqc]

I agree that this is a complex task and most likely not all parts of stdlib could be pollyfilled this way.

Maybe providing a hook for other plugins to rewrite static stdlib references? A lot of useful things fall into this category: List/Map.of, Optional.stream(), Optional.or(), etc. This is different then JSR-354 or https://www.threeten.org/threetenbp/ because those are separate packages - you can just include them on older JVM. You can't do the same with List#of()

[cruftex]

A lot of useful things fall into this category: List/Map.of, Optional.stream(), Optional.or(), etc.

Just have the spark of an idea: For simple things like the above it would be possible to create refactoring rules via: https://errorprone.info/docs/refaster

[tlinkowski]

Hi, you might be interested in UniJ, which provides a backport of JDK 9+ APIs in the form of a facade.

E.g. UniLists.of(1, 2) corresponds to List.of(1, 2). At runtime, it delegates to:

• either List.of(1, 2) (for JDK 9+)
• or Collections.unmodifiableList(Arrays.asList(1, 2)) (for JDK 8)

If:

• you added a dependency on UniJ
• and Jabel could rewrite List.of references into UniLists.of ones

you'd achieve the effect you want.

Instance methods (like Optional.stream()) would be much more problematic to rewrite, though.

Disclaimer: I'm the author of UniJ.