Scala 2.13.8

The Scala team at Lightbend is pleased to announce the availability of Scala 2.13.8.

This is a modest, incremental release focused on addressing regressions in 2.13.7.

Highlights

• Make REPL work again on Mac M1 (upgrade JLine & JNA) (#9807 by @SethTisue)
• Fix slicing of views of IndexedSeqs (including fixing 2.13.7 reverseIterator regression) (#9799 by @som-snytt)
• Fix 2.13.7 regression in implicit resolution (#9829 by @joroKr21)
• Fix 2.13.7 releaseFence regression affecting GraalVM compatibility (#9825 by @lrytz)
• Fix 2.13.7 regression affecting wildcards and F-bounded types (#9806 by @joroKr21)

A few small changes that will ship in 2.12.16 are also included in this release.

For the complete 2.13.8 change lists, see all merged PRs and all closed bugs.

Compatibility

As usual for our minor releases, Scala 2.13.8 is binary-compatible with the whole Scala 2.13 series.

Upgrading from 2.12? Enable -Xmigration while upgrading to request migration advice from the compiler.

Contributors

A big thank you to everyone who's helped improve Scala by reporting bugs, improving our documentation, spreading kindness in discussions around Scala, and submitting and reviewing pull requests! You are all magnificent.

This release was brought to you by 8 contributors, according to git shortlog -sn --no-merges @ ^v2.13.7 ^2.12.x. Thank you A. P. Marki, Seth Tisue, Georgi Krastev, Jason Zaugg, Lukas Rytz, Martijn Hoekstra, Philippus Baalman, Chris Kipp.

Thanks to Lightbend for their continued sponsorship of the Scala core team’s efforts. Lightbend offers commercial support for Scala.

Scala 2.13 notes

The release notes for Scala 2.13.0 have important information applicable to the whole 2.13 series.

Obtaining Scala

Scala releases are available through a variety of channels, including (but not limited to):

• Bump the scalaVersion setting in your sbt-based project
• Download a distribution from scala-lang.org
• Obtain JARs via Maven Central

Scala 2.13.7

The Scala team at Lightbend is pleased to announce the availability of Scala 2.13.7.

Align with Scala 3

• Update TASTy reader to support Scala 3.1 (#9791 by @bishabosha)
• Allow import x.{*, given} under -Xsource:3 (#9724 by @smarter)
• Allow case in pattern bindings even without -Xsource:3 (#9721 by @smarter)
• Deprecate top-level wildcard type parameters (#9712 by @som-snytt)

JDK and Java compatibility

• Support JDK 18 (#9702 by @SethTisue)
• Support JDK 16 records in Java sources (#9551 by @harpocrates)
• Allow concrete private interface methods in Java sources (#9748 by @dengziming)
• Use StringConcatFactory for string concatenation on JDK 9+ (#9556 by @harpocrates)

Android compatibility

• Add ClassValueCompat to support systems without java.lang.ClassValue (such as Android) (#9752 by @nwk37011)
• For Android compatibility, make Statics.releaseFence() also catch NoSuchMethodException for java.lang.invoke.VarHandle.releaseFence() call (#9739 by @nwk37011)

Concurrency

• Fix asymmetric failure behavior of Future#{zip,zipWith,traverse,sequence} by making them fail fast regardless of ordering (#9655 by @lihaoyi)

Collections

• Make ArrayBuffer's iterator fail fast when buffer is mutated (#9258 by @NthPortal)
• Fix ArrayOps bugs (by avoiding ArraySeq#array, which does not guarantee element type) (#9641 by @som-snytt)
• Deprecate IterableOps.toIterable (#9774 by @lrytz)

Other changes

• Accept supplementary Unicode characters in identifiers (#9687 by @som-snytt)
• Improve tab completion and code assist in REPL (#9656 by @retronym)

Some small changes that will ship in 2.12.16 are also included in this release.

For the complete 2.13.7 change lists, see all merged PRs and all closed bugs.

Compatibility

As usual for our minor releases, Scala 2.13.7 is binary-compatible with the whole Scala 2.13 series.

Upgrading from 2.12? Enable -Xmigration while upgrading to request migration advice from the compiler.

Contributors

A big thank you to everyone who's helped improve Scala by reporting bugs, improving our documentation, spreading kindness in discussions around Scala, and submitting and reviewing pull requests! You are all magnificent.

This release was brought to you by 25 contributors, according to git shortlog -sn --no-merges @ ^v2.13.6 ^2.12.x. Thank you A. P. Marki, Lukas Rytz, Seth Tisue, Jason Zaugg, Jamie Thompson, NthPortal, Georgi Krastev, Guillaume Martres, Dale Wijnand, Martijn Hoekstra, Alec Theriault, Rafał Sumisławski, Matt Dziuban, Li Haoyi, Doug Roper, Sébastien Doeraene, VladKopanev, danicheg, dengziming, megri, nwk37011, Magnolia.K, 梦境迷离, Mathias, James Judd.

Thanks to Lightbend for their continued sponsorship of the Scala core team’s efforts. Lightbend offers commercial support for Scala.

Scala 2.13 notes

The release notes for Scala 2.13.0 have important information applicable to the whole 2.13 series.

Obtaining Scala

Scala releases are available through a variety of channels, including (but not limited to):

• Bump the scalaVersion setting in your sbt-based project
• Download a distribution from scala-lang.org
• Obtain JARs via Maven Central

Scala 2.12.15

This release improves compatibility with JDK 17 and 18:

• Avoids IllegalArgumentException in JDK 17+ for lambda deserialization (#9676)
• Upgrades to ASM 9.2, for JDK 18 support in optimizer (#9701)

and facilitates cross-building with Scala 3 with:

• Allow case in pattern bindings even without -Xsource:3 (#9740 by @smarter)
• Allow import x.{*, given} under -Xsource:3 (#9736 by @smarter)
• Handle star in import selector (under -Xsource:3) (#9665 by @som-snytt)

For complete 2.12.15 change lists, see all merged PRs and all closed bugs.

Compatibility

As usual for our minor releases, Scala 2.12.15 is binary-compatible with the whole Scala 2.12 series.

Contributors

A big thank you to everyone who's helped improve Scala by reporting bugs, improving our documentation, spreading kindness in discussions around Scala, and submitting and reviewing pull requests! You are all magnificent.

This release was brought to you by 4 contributors, according to git shortlog -sn --no-merges @ ^v2.12.14 ^2.11.x. Thank you Jason Zaugg, Seth Tisue, A.P. Marki, Guillaume Martres.

Thanks to Lightbend for their continued sponsorship of the Scala core team’s efforts. Lightbend offers commercial support for Scala.

Scala 2.12 notes

The release notes for Scala 2.12.0 have important information applicable to the whole 2.12 series.

Obtaining Scala

Scala releases are available through a variety of channels, including (but not limited to):

• Bump the scalaVersion setting in your sbt-based project
• Download a distribution from scala-lang.org
• Obtain JARs via Maven Central

Scala 2.12.14

• Backports improvements to -Xsource:3 to help projects cross build between 2.12.x, 2.13.x and 3.x.
  (#9589, #9595 and #9620 by @smarter and @neko-kai)
• Reduces lock contention between compilers when reading classpath JAR files. (#9549 by @retronym)
• Propagate custom TaskSupport through operations of parallel collections. (#9529, backport of fix for scala/scala-parallel-collections#152, by @lrytz)
• Upgrade to asm 9.1, for JDK 17 support (#9488 by @SethTisue)
• Fix cyclic error in runtime reflection (protobuf), a regression that prevented Spark upgrading to 2.12.13 (#9478 by @retronym)
• Allow annotated literals inside as annotation args. (#9342 by @gzm0)

For complete 2.12.14 change lists, see all merged PRs and all closed bugs.

Compatibility

As usual for our minor releases, Scala 2.12.14 is binary-compatible with the whole Scala 2.12 series.

Contributors

A big thank you to everyone who's helped improve Scala by reporting bugs, improving our documentation, spreading kindness in discussions around Scala, and submitting and reviewing pull requests! You are all magnificent.

This release was brought to you by 40 contributors, according to git shortlog -sn --no-merges HEAD ^v2.12.13 ^2.11.x. Thank you Jason Zaugg, Lukas Rytz, Guillaume Martres, Dale Wijnand, Seth Tisue, A. P. Marki, Mike Skells, Tom Grigg, Kai, Mario Galic, Martijn Hoekstra, tanishiking, Philippus, Adriaan Moors, Sébastien Doeraene, Tobias Schlatter, Andrii, Filipe Regadas, Alexey Kotlyarov.

Thanks to Lightbend for their continued sponsorship of the Scala core team’s efforts. Lightbend offers commercial support for Scala.

Scala 2.12 notes

The release notes for Scala 2.12.0 have important information applicable to the whole 2.12 series.

Obtaining Scala

Scala releases are available through a variety of channels, including (but not limited to):

• Bump the scalaVersion setting in your sbt-based project
• Download a distribution from scala-lang.org
• Obtain JARs via Maven Central

Scala 2.13.6

The Scala 2 team at Lightbend is pleased to announce the availability of Scala 2.13.6.

Highlights

• TASTy Reader support for Scala 3.0.0 (#9617 by @bishabosha)
• The splain compiler plugin by @tek was integrated into the compiler, available with the -Vimplicits and -Vtype-diffs flags (#7785)
• Escaped double quotes now work as expected in string interpolations, both s"\"" and s"$"" (#8830 by @eed3si9n and #9536 by @martijnhoekstra)

Other Changes

• Optimized BigInt implementation (#9628) by @denisrosset
• Support JDK15 text blocks in Java parser (#9548) by @harpocrates
• Stricter override checking for protected Scala members which override Java members (#9525) by @kynthus
• Check private[this] members in override checking (#9542)
• More accurate outer checks in patterns (#9504)
• Allow renaming imports from _root_ (#9482) by @som-snytt
• Make more annotations extend ConstantAnnotation (9336) by @BalmungSan
• A number of syntax changes were added to simplify cross-building between Scala 2 and 3
  • Don't error (only warn) on symbol literals under -Xsource:3 (#9602)
  • Support writing & instead of with in types under -Xsource:3 (#9594)
  • Support Scala 3 vararg splice syntax under -Xsource:3 (#9584)
  • Support Scala 3 wildcard and renaming imports under -Xsource:3 (#9582)
  • Allow soft keywords open and infix under -Xsource:3 (#9580)
  • Align leading infix operator with Scala 3 improvements (#9567)
  • Support ? as wildcard marker under -Xsource:3 (#9560)
  • Support case in pattern bindings under -Xsource:3 (#9558)
  • Parse +_ and -_ in types as identifiers under -Xsource:3 to support Scala 3.2 placeholder syntax (#9605)

Some small changes that will ship in 2.12.14 are also included in this release.

For the complete 2.13.6 change lists, see all merged PRs and all closed bugs.

Compatibility

As usual for our minor releases, Scala 2.13.6 is binary-compatible with the whole Scala 2.13 series.

Upgrading from 2.12? Enable -Xmigration while upgrading to request migration advice from the compiler.

Contributors

A big thank you to everyone who's helped improve Scala by reporting bugs, improving our documentation, spreading kindness in discussions around Scala, and submitting and reviewing pull requests! You are all magnificent.

This release was brought to you by 25 contributors, according to git shortlog -sn --no-merges HEAD ^v2.13.5 ^2.12.x. Thank you A. P. Marki, Lukas Rytz, Dale Wijnand, Jamie Thompson, Seth Tisue, 梦境迷离, Guillaume Martres, Martijn Hoekstra, Denis Rosset, Aaron S. Hawley, Kai, Eugene Yokota, Jason Zaugg, Anatolii Kmetiuk, Ikko Ashimine, superseeker13, Eugene Platonov, Diego E. Alonso Blas, Filipe Regadas, Hatano Yuusuke, Luis Miguel Mejía Suárez, Rafał Sumisławski, Alec Theriault, Tom Grigg, Torsten Schmits.

Thanks to Lightbend for their continued sponsorship of the Scala core team’s efforts. Lightbend offers commercial support for Scala.

Scala 2.13 notes

The release notes for Scala 2.13.0 have important information applicable to the whole 2.13 series.

Obtaining Scala

Scala releases are available through a variety of channels, including (but not limited to):

• Bump the scalaVersion setting in your sbt-based project
• Download a distribution from scala-lang.org
• Obtain JARs via Maven Central

Scala 2.13.5

Scala 2.13.5

The Scala 2 team at Lightbend is pleased to announce the availability of Scala 2.13.5.

Highlights

• TASTy reader: add support for Scala 3.0.0-RC1 (#9501, #9394, #9357) — thank you @bishabosha!
• Allow name-based extractors to be irrefutable (#9343) — thank you @martijnhoekstra!
• Upgrade to ASM 9.1, for JDK 16 and 17 support in the optimizer (#9489, #9480)

Other changes

• Assorted improvements to exhaustivity checking in pattern matching (#9479, #9472, #9474, #9313, #9462)
• Assorted improvements to handling of higher-kinded types, aligning with Scala 3 (#9400, #9404, #9405, #9414, #9417, #9439) — thank you @joroKr21!
• Make -target support JVM 13, 14, 15, 16, and 17 (#9489, #9481)
• Omit @nowarn annotations from generated code, for forwards compatibility at compile-time (#9491)
• Add linting of unused context bounds (via -Wunused:synthetics or -Wunused:params) (#9346) — thank you @som-snytt!
• Lift artificial restrictions on ConstantAnnotations (#9379)
• Make Java Map wrappers handle nulls according to put/remove contract (#9344) — thank you @som-snytt!
• Make language specification available as a PDF (#7432) — thank you @sake92!

Some small changes that will ship in 2.12.14 are also included in this release.

For complete 2.13.5 change lists, see all merged PRs and all closed bugs.

Compatibility

As usual for our minor releases, Scala 2.13.5 is binary-compatible with the whole Scala 2.13 series.

Upgrading from 2.12? Enable -Xmigration while upgrading to request migration advice from the compiler.

Contributors

A big thank you to everyone who's helped improve Scala by reporting bugs, improving our documentation, spreading kindness in discussions around Scala, and submitting and reviewing pull requests! You are all magnificent.

This release was brought to you by 23 contributors, according to git shortlog -sn --no-merges HEAD ^v2.13.4 ^2.12.x. Thank you Seth Tisue, A. P. Marki, Dale Wijnand, NthPortal, Jamie Thompson, Lukas Rytz, Martijn Hoekstra, Georgi Krastev, Jason Zaugg, Jasper Moeys, Sakib Hadziavdic, Anatolii Kmetiuk, Arnaud Gourlay, Marcono1234, Chia-Ping Tsai, Mike Skells, Stefan Zeiger, Waleed Khan, Yann Bolliger, Guillaume Martres, 梦境迷离, Ethan Atkins, Darcy Shen.

Thanks to Lightbend for their continued sponsorship of the Scala core team’s efforts. Lightbend offers commercial support for Scala.

Scala 2.13 notes

The release notes for Scala 2.13.0 have important information applicable to the whole 2.13 series.

Obtaining Scala

Scala releases are available through a variety of channels, including (but not limited to):

• Bump the scalaVersion setting in your sbt-based project
• Download a distribution from scala-lang.org
• Obtain JARs via Maven Central

Scala 2.12.13

Highlights

• Adds support for configurable warnings and errors (@nowarn and -Wconf), backported from 2.13

For a tour of this capability, consult this blog post by Lukas Rytz.

Standard library

• To permit compiling on JDK 15, avoid clash with new CharSequence#isEmpty method #9292
  • The clash is avoided by making CharSequence wrappers in Predef non-implicit.
  • The change is binary compatible, but not source compatible. Call sites may need updating.
  • The same change was included in Scala 2.13.4.

Other changes

• Improves pattern matching exhaustivity warnings for patterns involving tuples
• Improves performance of building immutable.{TreeMap,TreeSet} by using mutation within the builder

For complete 2.12.13 change lists, see all merged PRs and all closed bugs.

Compatibility

As usual for our minor releases, Scala 2.12.13 is binary-compatible with the whole Scala 2.12 series.

The internal implementation of groupBy has been optimized to reduce allocations. This can result in different ordering elements if you iterate the resulting Map. The ordering of the returned map is not specified behaviour and should not be relied upon, for ordering sensitive use cases consider building a LinkedHashMap or TreeMap instead.

Contributors

A big thank you to everyone who's helped improve Scala by reporting bugs, improving our documentation, spreading kindness in discussions around Scala, and submitting and reviewing pull requests! You are all magnificent.

This release was brought to you by 40 contributors, according to git shortlog -sn --no-merges HEAD ^v2.12.12 ^2.11.x. Thank you Mike Skells, Jason Zaugg, Lukas Rytz, Dale Wijnand, A. P. Marki, Harrison Houghton, Darcy Shen, Seth Tisue, Ivano Pagano, João Ferreira, Ethan Atkins, NthPortal.

Thanks to Lightbend for their continued sponsorship of the Scala core team’s efforts. Lightbend offers commercial support for Scala.

Scala 2.12 notes

The release notes for Scala 2.12.0 have important information applicable to the whole 2.12 series.

Obtaining Scala

Scala releases are available through a variety of channels, including (but not limited to):

• Bump the scalaVersion setting in your sbt-based project
• Download a distribution from scala-lang.org
• Obtain JARs via Maven Central

Scala 2.13.4

Scala 2.13.4:

• Restores default global ExecutionContext to 2.12 behavior
• Improves pattern matching, especially in exhaustivity checking
• Adds experimental support for consuming some libraries built by Scala 3

and more! Details below.

Concurrency

NOTE The following change affects parallelism and performance. If you use scala.concurrent.ExecutionContext.global you may
want to adapt your code. (But note that Akka is unaffected, because it uses its own execution contexts.)

In 2.13.0 we made ExecutionContext.global "opportunistic". This enabled "batching" of nested tasks
to execute on the same thread, avoiding an expensive context switch. That strategy requires
user code to wrap long-running and/or blocking tasks with blocking { ... } to maintain parallel
execution.

For 2.13.4, we restore 2.12's default non-batching behavior, which is safer for arbitrary user code. Users wanting
increased performance may override the default, if they believe their code uses blocking correctly.
We make that choice available via ExecutionContext.opportunistic.

Using ExecutionContext.opportunistic requires a bit of extra boilerplate, made necessary by binary
compatibility constraints on the standard library. Detailed instructions are in
ExecutionContext.global's Scaladoc.

Further detail: #9270/#9296/scala/bug#12089,

Pattern matching

The pattern matcher is now much better at warning you if a match isn't exhaustive.

The following types of matches no longer disable exhaustivity checking:

• guards (case <pattern> if <condition> => ...) #9140
• custom extractors (user-defined unapply or unapplySeq) #9140/#9162
• unsealed types, if you opt in via -Xlint or -Xlint:strict-unsealed-patmat #9140/#9299

Additionally,

• private classes are now treated as if sealed #9211
• singleton types no longer prematurely widen #9209
• tuples are handled properly #9147/#9163/#9147

New warnings reported can be resolved by:

1. adding any missing cases
2. in the case of complementary guards (e.g. if n > 0 and if n <= 0) by dropping the last guard
3. for custom extractors: demarking irrefutable extractors as such, by defining the return type as Some
4. for sealed types: marking traits or parent classes sealed, parent classes abstract, and classes final
5. explicitly declaring the default case: case x => throw new MatchError(x)

Otherwise, your options for suppressing warnings include:

1. annotate the scrutinee with @unchecked, such as (foo: @unchecked) match { ... }
2. disable exhaustivity checking in the presence of guards and custom extractors with -Xnon-strict-patmat-analysis
3. disable exhaustivity checking of unsealed types with -Xlint:-strict-unsealed-patmat
4. use -Wconf to suppress the warnings globally, with e.g. -Wconf:msg=match may not be exhaustive:i

Scala 3 interop

This release enables the Scala 2 compiler to consume some libraries built in Scala 3. #9109/#9293

The new capability is experimental. To enable it, add -Ytasty-reader to your compiler options.

Not all Scala 3 built libraries are supported, because not all Scala 3 features can be supported.
The library author must stay within the supported subset.

For more details and caveats see the blog post Forward Compatibility for the Scala 3 Transition.

Standard library changes

• When compiling on JDK 15, avoid clash with new CharSequence#isEmpty method #9292
  • The clash is avoided by making CharSequence wrappers in Predef non-implicit.
  • The change is binary compatible, but not source compatible. Call sites may need updating.
• Make LazyList.cons.apply lazier #9095
• Make MapView#values preserve laziness #9090
• Make ListBuffer's iterator fail when the buffer is mutated #9174
• Un-deprecate useful StringOps methods, despite Unicode concerns #9246

Compiler changes

• Allow using classOf with object type (e.g. classOf[Foo.type]) #9279
• Fix back-quoted constructor params with identical prefixes #9008
• Enable range positions (-Yrangepos) by default #9146

Other changes

Some changes that will also ship in 2.12.13 are also included in this release, most notably:

• When compiling on JDK 15, avoid clash with new CharSequence#isEmpty method #9292
  • To avoid the clash, implicit was removed from Predef's implicit conversions to SeqCharSequence and ArrayCharSequence.
  • This change is binary compatible, but not source compatible. User code may need updating. See PR for details.

For complete 2.13.4 change lists, see all merged PRs and all closed bugs.

Compatibility

As usual for our minor releases, Scala 2.13.4 is binary-compatible with the whole Scala 2.13 series.

Upgrading from 2.12? Enable -Xmigration while upgrading to request migration advice from the compiler.

Contributors

A big thank you to everyone who's helped improve Scala by reporting bugs, improving our documentation, spreading kindness in discussions around Scala, and submitting and reviewing pull requests! You are all magnificent.

This release was brought to you by 40 contributors, according to git shortlog -sn --no-merges HEAD ^v2.13.3 ^2.12.x. Thank you Jamie Thompson, Dale Wijnand, A. P. Marki, NthPortal, Lukas Rytz, Seth Tisue, Jason Zaugg, Georgi Krastev, Eugene Yokota, Martijn Hoekstra, Trey Cahill, Rado Buransky, Ergys Dona, Mike Skells, Greg Pfeil, Kazuhiro Sera, Mitsuhiro Shibuya, NagaChaitanya Vellanki, Sergei Petunin, Sébastien Doeraene, Takahashi Osamu, Viktor Klang, mwielocha, Nicolas Stucki, Jan Arne Sparka, Philippus Baalman, Glenn Liwanag, Rafał Sumisławski, Renato Cavalcanti, Sergei, nooberfsh, Dmitrii Naumenko, Simão Martins, counter2015, Jian Lan, Liu Fengyun, Kanishka, Julien Richard-Foy, Janek Bogucki, Björn Regnell.

Thanks to Lightbend for their continued sponsorship of the Scala core team’s efforts. Lightbend offers commercial support for Scala.

Scala 2.13 notes

The release notes for Scala 2.13.0 have important information applicable to the whole 2.13 series.

Obtaining Scala

Scala releases are available through a variety of channels, including (but not limited to):

• Bump the scalaVersion setting in your sbt-based project
• Download a distribution from scala-lang.org
• Obtain JARs via Maven Central

Scala 2.12.12

Highlights

This release adds compiler support for scala-async and backports substantial performance improvements to collections.

• The compiler now includes a phase that performs the transformation for the async/await DSL for working with Scala Futures.
  This transform is based on the macro implementation in scala-async but has been substantially rewritten to fix some
  long standing bugs, reduce the overhead of compilation and simplify the extension points for third party effect systems.
  scala-async 1.0.0 will be released shortly building atop this phase. (#8816)
• immutable.{TreeSet, TreeMap} are now based on a backport of the 2.13.x implementation. (#8749)
• The builders for immutable.{HashMap, HashSet} are more efficient -- they now use mutation during building to reduce memory churn. (#8726)

Further highlights

• Minor improvements to compiler performance. The allocation rate of the compiler is reduced by 10%.

This is not a complete list of changes. For that, see all merged PRs and all closed bugs.

Compatibility

As usual for our minor releases, Scala 2.12.12 is binary-compatible with the whole Scala 2.12 series.

Contributors

A big thank you to everyone who's helped improve Scala by reporting bugs, improving our documentation,
spreading kindness in discussions around Scala, and submitting and reviewing pull requests! You are all magnificent.

This release was brought to you by 13 contributors, according to git shortlog -sn --no-merges v2.12.11..v2.12.12. Thank you Jason Zaugg, Mike Skells, Lukas Rytz, Harrison Houghton, Adriaan Moors, Stefan Zeiger, Dale Wijnand, Seth Tisue, A. P. Marki, Eugene Yokota, NthPortal, Georgi Krastev and Martijn Hoekstra.

Thanks to Lightbend for their continued sponsorship of the Scala core team’s efforts. Lightbend offers commercial support for Scala.

Scala 2.12 notes

The release notes for Scala 2.12.0 have important information applicable to the whole 2.12 series.

Obtaining Scala

Scala releases are available through a variety of channels, including (but not limited to):

• Bump the scalaVersion setting in your sbt-based project
• Download a distribution from scala-lang.org
• Obtain JARs via Maven Central

Scala 2.13.3

Scala 2.13.3 is primarily a bugfix release.

It also includes:

• improvements to warnings and linting
• experimental -Xasync support

For more detail, read on.

Behavior changes

• Symbol#toString is now Symbol(foo) instead of the deprecated single-quote form 'foo (#8933)

Bugfixes

• Fix 2.13-only bug in Java collection converters that caused some operations to perform an extra pass (#9058)
• Fix 2.13.2 performance regression in Vector: restore special cases for small operands in appendedAll and prependedAll (#9036)
• Increase laziness of #:: for LazyList (#8985)
• Allow trailing backslash in string interpolators (#8942)
• Respect @uncheckedVariance in higher-kinded types (fixing 2.13.2 regression) (#8938)

Warnings and linting

• Deprecate auto-application of (non-Java-defined) methods with a single empty parameter list (#8833)
  • The PR has instructions for suppressing the warning if it is unwanted
• Warn by default on mismatch of presence/absence of an empty parameter list when overriding (#8846)
  • -Xlint:nullary-override is no longer accepted, since this now warns by default
• Discourage multi-argument infix syntax: lint applications (x op (a, b)), also lint operator-name definitions (#8951)
• Fix @nowarn to use correct semantics for & (#9032)
• Make -Wunused:imports work again even when -Ymacro-annotations is enabled (#8962)
• Replace -Wself-implicit with -Xlint:implicit-recursion (#9019)
• Under -Xsource:3, disallow auto-eta-expansion of SAMs (#9049)

Experimental -Xasync

This successor to scala-async allows usage with other effect systems besides scala.concurrrent.Future.

• Compiler support for scala-async; enable with -Xasync (#8816)

We will publish a blog post with more detail on this work by @retronym, building on his earlier collaboration with @phaller. In the meantime, see the PR description.

This feature will also be included in the 2.12.12 release.

Other changes

For complete 2.13.3 change lists, see all merged PRs and all closed bugs.

Some changes that will ship in 2.12.12 are also included in this release, most notably:

• Annotation parsing & @Deprecated (#8781)
• Fix Scaladoc tool on JDK 11 with -release 8: exclude sig files in Symbol#sourceFile (#8849)

Compatibility

As usual for our minor releases, Scala 2.13.3 is binary-compatible with the whole Scala 2.13 series.

Upgrading from 2.12? Enable -Xmigration during upgrade to request migration advice from the compiler.

Contributors

A big thank you to everyone who's helped improve Scala by reporting bugs, improving our documentation, spreading kindness in discussions around Scala, and submitting and reviewing pull requests! You are all magnificent.

This release was brought to you by 28 contributors, according to git shortlog -sn --no-merges HEAD ^v2.13.2 ^2.12.x. Thank you A. P. Marki, Jason Zaugg, Seth Tisue, Dale Wijnand, Lukas Rytz, Georgi Krastev, David Barri, Eugene Yokota, Diego E. Alonso Blas, Akhtiam Sakaev, Glenn Liwanag, changvvb, Evgeny Ganchurin, Mike Skells, Martijn Hoekstra, yudedako, Anatolii Kmetiuk, Gilles Peiffer, JyotiSachdeva.ext, Karol Chmist, Kenji Yoshida, Lorenzo Costanzia di Costigliole, NthPortal, Steven Barnes, Sébastien Doeraene, Travis Brown, counter2015, nogurenn.

Thanks to Lightbend for their continued sponsorship of the Scala core team’s efforts. Lightbend offers commercial support for Scala.

Scala 2.13 notes

The release notes for Scala 2.13.0 have important information applicable to the whole 2.13 series.

Obtaining Scala

Scala releases are available through a variety of channels, including (but not limited to):

• Bump the scalaVersion setting in your sbt-based project
• Download a distribution from scala-lang.org
• Obtain JARs via Maven Central