Update scala-compiler, scala-library, ... to 2.12.21

[scala-steward-bot]

About this PR

📦 Updates

• org.scala-lang:scala-compiler
• org.scala-lang:scala-library
• org.scala-lang:scala-reflect

from 2.12.20 to 2.12.21

📜 GitHub Release Notes - Version Diff

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^{labels: library-update, early-semver-patch, semver-spec-patch, commit-count:1}

Summary by CodeRabbit

• Chores
  • Updated Scala 2.12 support from version 2.12.20 to 2.12.21.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

Updated the Scala 2.12 patch version in build configuration from 2.12.20 to 2.12.21. No other build settings or dependencies were modified.

Changes

Cohort / File(s)	Change Summary
Build Configuration build.sbt	Updated crossScalaVersions in buildSettings: Scala 2.12 version bumped from 2.12.20 to 2.12.21

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Possibly related PRs

• Update scala-compiler, scala-library, ... to 2.12.20 #79: Both PRs bump the Scala 2.12 patch version in build.sbt's crossScalaVersions (2.12.19→2.12.20 vs. 2.12.20→2.12.21).
• Update scala-compiler, scala-library, ... to 2.13.16 #91: Both PRs modify the same build.sbt crossScalaVersions setting to update Scala versions.
• Update scala-compiler, scala-library, ... to 2.13.17 #107: Both PRs update Scala patch versions in build.sbt's buildSettings.crossScalaVersions.

Suggested reviewers

• xuwei-k

Poem

🐰 A patch so small, a version bump so bright,
From twenty to twenty-one, we climb to new height!
Scala 2.12 gets a little refresh,
Our build now runs with the newest mesh. ✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: updating Scala library dependencies from 2.12.20 to 2.12.21, which directly aligns with the build.sbt modification and PR objectives.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[coderabbitai]

Actionable comments posted: 1

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 7f89689 and 4edcc5d.

📒 Files selected for processing (1)

• build.sbt (1 hunks)

[coderabbitai]

⚠️ Potential issue | 🔴 Critical

🧩 Analysis chain

🌐 Web query:

Scala 2.12.21 release

💡 Result:

Short answer: Scala 2.12.21 is planned but (as of Dec 8, 2025) not yet published as a final release. A release candidate / nightlies exist and the project scheduled the official publish for Dec 8, 2025; the Scala website and JDK-compatibility docs still list 2.12.20 as the latest stable 2.12.x. [1][2]

Sources

• Scala contributors release-planning thread (2.12.21; RC and proposed Dec 8, 2025 publish). [1]
• Scala JDK compatibility / downloads pages (latest stable 2.12.x = 2.12.20; 2.12.21 marked forthcoming/nightlies). [2]

---

Do not merge—Scala 2.12.21 was not officially released at the time this PR was created.

At the PR date (Dec 8, 2025), Scala 2.12.21 existed only as a release candidate and nightlies; the official stable release was scheduled for publication on Dec 8 but had not yet been published. The Scala website and JDK compatibility documentation still listed 2.12.20 as the latest stable 2.12.x version. Using a pre-release version in crossScalaVersions risks build failures due to version unavailability in Maven Central and potential instability. Wait for official release confirmation before updating.

🤖 Prompt for AI Agents

In build.sbt around line 33, the crossScalaVersions list includes "2.12.21"
which was not an official stable release at PR time; revert the entry to the
last published stable 2.12 release (e.g., replace "2.12.21" with "2.12.20") or
remove the 2.12.21 element entirely until the official release is confirmed and
available in public repositories, then update the list to the new version.