Sourced from scala-library's releases.

Scala 2.13.9

The following changes are highlights of this release:

Regression

After release, it was discovered that Scala 2.13.9 has a regression, primarily affecting library maintainers, where binary-incompatible bytecode is emitted for case classes which are also value classes (case class ... extends AnyVal). 2.13.10 is coming soon to address the problem. For details, and to follow progress on the release, visit https://contributors.scala-lang.org/t/scala-2-13-10-release-planning/5943.

Compatibility with Scala 3

• Tasty Reader: Add support for Scala 3.2 (#10068)
• Tasty Reader: Restrict access to experimental definitions (#10020)
• To aid cross-building, accept and ignore using in method calls (#10064 by @​som-snytt)
• To aid cross-building, allow ? as a wildcard even without -Xsource:3 (#9990)
• Make Scala-3-style implicit resolution explicitly opt-in rather than bundled in -Xsource:3 (#10012 by @​povder)
• Prefer type of overridden member when inferring (under -Xsource:3) (#9891 by @​som-snytt)

JDK version support

• Make -release more useful, deprecate -target, align with Scala 3 (#9982 by @​som-snytt)
• Support JDK 19 (#10001 by @​Philippus)

Warnings and lints

• Add -Wnonunit-statement to warn about discarded values in statement position (#9893 by @​som-snytt)
• Make unused-import warnings easier to silence (support filtering by origin=) (#9939 by @​som-snytt)
• Add -Wperformance lints for *Ref boxing and nonlocal return (#9889 by @​som-snytt)

Language improvements

• Improve support for Unicode supplementary characters in identifiers and string interpolation (#9805 by @​som-snytt)

Compiler options

• Use subcolon args to simplify optimizer options (#9810 by @​som-snytt)
• For troubleshooting compiler, add -Vdebug-type-error (and remove -Yissue-debug) (#9824 by @​tribbloid)

Security

• Error on source files with Unicode directional formatting characters (#10017)
• Prevent Function0 execution during LazyList deserialization (#10118)

Bugfixes

• Emit all bridge methods non-final (perhaps affecting serialization compat) (#9976)
• Fix null-pointer regression in Vector#prependedAll and Vector#appendedAll (#9983)
• Improve concurrent behavior of Java ConcurrentMap wrapper (#10027 by @​igabaydulin)
• Preserve null policy in wrapped Java Maps (#10129 by @​som-snytt)

Changes that shipped in Scala 2.12.16 and 2.12.17 are also included in this release.

... (truncated)

• 4905801 Merge pull request #10182 from som-snytt/issue/7481-nospec-array
• 69bff24 Test for old crasher
• cd52542 Merge pull request #10175 from liang3zy22/bug12509
• d23620a Avoid parsing code comment twice
• 455e792 Merge pull request #10172 from flomebul/TraversalIsDeprecated
• d89e3d4 Replace "Traversable" by corresponding "Iterable" in doc comments.
• 9ee4b60 Merge pull request #10163 from liang3zy22/scalacheckbugs
• 439a981 Merge pull request #10169 from som-snytt/issue/9069-view-slice
• 0fffd1f Merge pull request #10170 from som-snytt/issue/9931-test
• 9f3ffcf Merge pull request #10164 from som-snytt/dev/814-redux-args-file
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