Highlights of the release

• Support for JDK 24 #22250
• REPL :silent command to toggle automatic printing of outputs #22248
• REPL --repl-init-script: setting to run a code on startup #22206
• Deprecated setting -Xno-decode-stacktraces is now an alias to -Xno-enrich-error-messages #22208
• Annotation arguments are no longer lifted #22035
• Experimental Capture Checking: Implement tracked members #21761

Breaking changes

• Align @implicitNotFound and @implicitAmbigous with the language specification #22371

This change may impact users who previously used these annotations using variables or string interpolation.

Previously, a bug in the Scala 3 compiler allowed non-literal strings to be passed as arguments to the @implicitNotFound and @implicitAmbiguous annotations. This could have affected how failed implicit search results were reported by the compiler.

Starting from Scala 3.6.4, the arguments for these annotations must be string literals. If a message is too long, it can be concatenated using the + operator, allowing for constant folding.

Other changes and fixes

Annotations

• Make sure symbols in annotation trees are fresh before pickling #22002
• Consider all arguments in Annotations.refersToParamOf #22001
• Do not lift annotation arguments (bis) #22046

Desugaring

• Fix [#22051]: only trust the type application part for case class unapplies #22099

Documentation

• Update example code linked to obsolete content in macros-spec.md #22256

Experimental: Capture Checking

• Fix [#21868], [#21869], and [#21870]: handle CapsOf in more places #21875
• Refine rules for capture parameters and members #22000
• Add a hint for using CC with REPL #22220
• Consolidate CC #21863

Experimental: Global Initialization

• Fix crash when initializing val in ByName closure #22354

Experimental: Named Tuples

• Handle TypeProxy of Named Tuples in unapply #22325
• Fail more eagerly when trying to adapt named unapply patterns #22315
• Widen singleton types when computing fields from .Fields #22149
• Fix .toTuple insertion #22028

Extension Methods

• Tweak ExtensionNullifiedByMember #22268
• Nowarn extension matching nonpublic member #21825

Implicits

• Rollback constraints in compareAppliedTypeParamRef #22339
• Try implicit searching after finding dynamic select #22318

Linting

• Allow discarding "Discarded non-Unit" warnings with : Unit #21927

Match Types

• Fix [#21841]: Check more that an unapplySeq on a NonEmptyTuple is valid. #22366
• Type avoidance in MT bound inference #22142

Metaprogramming

• Rethrow SuspendExceptions caught in CodeGen phase #22009

Metaprogramming: Compile-time

• Extend compiletime.testing.typechecks with certain transform phases #21185

Nullability

• Fix [#21619]: Refactor NotNullInfo to record every reference which is retracted once. #21624

Presentation Compiler

• Use new infer expected type for singleton complations #21421
• Fix match error in keyword completions #22138

Reflection

• Do not return java outline dummy constructor in primaryConstructor #22104

Reporting

• Normalise the types for Type Mismatch Error (E007) #22337
• Improve given search preference warning #22189
• Better error messages when an enum derives from AnyVal #22236
• Correctly print litteral types in the refined printer #22351

Rewrites

• Undo patch of double-block apply #21982

Scaladoc

• Scaladoc: Add support for named tuples #22263

Settings

• Limit exposure to ConcurrentModificationException when sys props are replaced or mutated #22180

Specification

• Align the spec to allow the marker #22323
• Integrate the specification for match types. #22164

Transform

• Fix [#22226]: Use classOf[BoxedUnit] for Unit array in ArrayConstructors. #22238

Typer

• Fixes for isLegalPrefix change #22241
• Resolve name when named imp is behind wild imps #21888

Contributors

Thank you to all the contributors who made this release possible 🎉

According to git shortlog -sn --no-merges 3.6.3..3.6.4 these are:

    46  Martin Odersky
    33  noti0na1
    24  Wojciech Mazur
    14  Dale Wijnand
    13  Matt Bovel
    11  Hamza Remmal
     7  Jan Chyb
     6  aherlihy
     5  Kacper Korban
     5  Seth Tisue
     5  Som Snytt
     4  Oliver Bračevac
     4  Yichen Xu
     3  Sébastien Doeraene
     3  dependabot[bot]
     3  kasiaMarek
     2  João Ferreira
     1  David Hua
     1  Eugene Flesselle
     1  Eugene Yokota
     1  Florian3k
     1  Jędrzej Rochala
     1  Kenji Yoshida
     1  Mathias
     1  Natsu Kagami
     1  Oleg Zenzin
     1  Piotr Chabelski
     1  Rui Chen
     1  philippus
     1  rochala
     1  xiaoshihou