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Propose guidance on choosing Scala between Scala LTS and Next. #154

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Propose guidance on choosing Scala between Scala LTS and Next. #154

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41 changes: 41 additions & 0 deletions proposals/032-scala-version-guidance.md
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date: May 2024
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# Provide guidance on choosing between Scala LTS and Next

## Proposer

Proposed by Zainab Ali, Community Representative, 14th May 2024.

## Abstract

There is no clear guidance on how to choose between Scala LTS or Scala Next. This has lead to some open source projects adopting Next where LTS is recommended. Examples include [xebiafunctional/fetch](https://github.com/xebia-functional/fetch/commit/60b26afb242b1e248615c811f2c23a51d6cab6fe), [kovstas/fs2-throttler](https://github.com/kovstas/fs2-throttler/commit/e265f6d585aa55d101ddd5e631abb940fccce084) and [cquiroz/scala-java-locales](https://github.com/cquiroz/scala-java-locales/issues/490).

The most prominent guidance in [the 2022 blog post on compatibility plans](https://www.scala-lang.org/blog/2022/08/17/long-term-compatibility-plans.html#the-future-best-practices) is outdated. [The 3.4.0 release notes](https://www.scala-lang.org/blog/2024/02/29/scala-3.4.0-and-3.3.3-released.html#-so-which-version-should-i-update-to) have better guidance, but are hard to discover.
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I think the problem with the 2022 isn't that it's outdated, but it's confusing because it's inconsistent in its messaging.

First it says:

The compiler team believes that the good answer for this question is always the newest one.

But in the later section it says:

Owners of commercial projects

We suggest you stick to the LTS version.

Library maintainers

Unless your library is built around some new language feature available only on Next, you should stick to the latest LTS version to have the broadest possible user base.

So while not everyone are owners of commercial projects or library maintainers, those two are the main active drivers of the Scala community (I think?), so it's confusing.

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This messaging around commercial projects is different to the release notes

If you are working on a project that is not meant to be used as an external dependency, feel free to update to Scala 3.4.0, especially if you are starting a new project.

This implies that new commercial projects should use 3.4.x as opposed to LTS.


## Proposal

The Scala website should include more guidance on choosing Scala versions. For example:
- There could be instructions on the [download page](https://www.scala-lang.org/download/) on choosing between LTS and Next.
- There could be an entry in the [migration guide](https://docs.scala-lang.org/scala3/guides/migration/compatibility-intro.html) on which version to choose.
- The [2022 blog post on compatibility plans](https://www.scala-lang.org/blog/2022/08/17/long-term-compatibility-plans.html#the-future-best-practices) could include a link to recent best practices.
Ideally, there should be a link to guidance wherever Next or LTS are mentioned.

Developers actively upgrading their Scala versions are unlikely to check the website, but do check other sources.
- There should be a link to guidance in the [release notes](https://github.com/scala/scala3/releases/tag/3.4.1).
- [Scala Steward's](https://github.com/scala-steward-org/scala-steward) PRs for Scala version upgrades could include explicit guidance and instructions on [pinning LTS](https://github.com/scala-steward-org/scala-steward/blob/main/docs/faq.md#how-can-version-updates-be-controlled).
- Build tools such as mill, sbt, and scala-cli could potentially inform the user if a jar is configured for publishing with a Next version.

## Cost

In level of difficulty I estimate the following order (from easiest to
hardest):

1. Updating guidance on the Scala website.
2. Updating Scala Steward's PR summary.
3. Including guidance in build tool publishing steps.

## Timescales

Updating guidance on the Scala website and release notes could be done quickly. As developers are currently in the process of adopting `3.4`, the earlier this guidance is available, the better.