Breaking changes

Don't infer implicits from non-accessible companion #25367
Enhance constant-folding during inlining #25731
Replace catching StackOverflowError with fuel #25937
Forbid this in top-level definitions #26448
Replace runtime.Rich* implicits on primitives by direct extension methods. #23872
Make -> sugar an inline method #24728
Make with type operator an error #26545
For bytecode generation, use stock ASM (not our old scala-asm fork) #26772

Highlights of the release

Add support for \s space escape #26515
Add support for //> using dep directives in the REPL (along with trailing code) #26507
Add .deb and .rpm packaging #26858
New stablized features:
- SIP 71: strictEqualityPatternMatching is now enabled by default default & add deprecation mechanics for -language feature flags #26424
New preview features:
- SIP 61: Unroll default arguments for binary compatibliy is now in preview #24903
- SIP 75: Relaxed lambda syntax is now in preview #26728
- SIP 68: Referenceable package objects is now preview #24586
New experimental features:
- Pre-SIP: Inline Traits & Specialized Traits #26156
- Pre-SIP: Modular AGentic Interface Code: Spec strings #26486

Other changes and fixes

Annotations

Add regression test for Java annotation @retention visibility (#389) #26339
Synthetic cast must not break tailrec #26343
Deprecate scala.annotation.strictfp #24839

Backend

More accurate generic signatures for boxed primitives #25944
Do not emit unnecessary fields for nested objects #25538
For bytecode generation, use stock ASM (not our old scala-asm fork) #25989
Layer JVM backend without cycles #26237

Desugaring

Use updated params when desugaring macro context bounds #26206

Scaladoc

Scaladoc: find members ending in ! or $ #26739
Scaladoc: Do not crash on class+module in API package #26766
Scaladoc: Do not allow resolving warnings to hide each other #26742
Scaladoc: Recursively unwrap exported trees #26737
Scaladoc: Stop hijacking link clicks #26664
Scaladoc: stay on the same page when switching versions #26762
Disable bogus Scaladoc warnings #26663

Documentation

Drop: remove access to Predef.any2stringadd #24656
Fixes to into doc #26203
Fix markdown code fences in PartialFunction.scala #26397
Util, io, ref (8): filled in @PARAM, @tparam, and @return tags that were missed last time #26127
Jdk (7): filled in @PARAM, @tparam, and @return tags that were missed last time #26126
Root files (9): filled in @PARAM, @tparam, and @return tags that were missed last time #26125
Collection immutable (3): filled in @PARAM, @tparam, and @return tags that were missed last time #26121
Collection mutable (2): filled in @PARAM, @tparam, and @return tags that were missed last time #26120
Quoted, compiletime (6): filled in @PARAM, @tparam, and @return tags that were missed last time #26124
Annotation, reflect, misc (11): fill in missing @PARAM, @tparam, and @return tags in Scaladoc comments #25381
Sys, concurrent, runtime (1): filled in @PARAM, @tparam, and @return tags that were missed last time #26119
Collection core (4): filled in @PARAM, @tparam, and @return tags that were missed last time #26122
Math (5): filled in @PARAM, @tparam, and @return tags that were missed last time #26123
Fix scaladoc link check for into #26207

Extension Methods

Fix: prevent infinite recursion in compareAppliedTypeParamRef #26608
Fix regression: more frequently cast the result of transparent inline #26684

Implicits

Also map types in Implicits.emitDictionary #26143

Incremental Compilation

Fixes #26340: Break cross-unit cyclic export across recompiled source siblings #26341

Inline

Fix fuel-related OpenCB issues #26898
Fix summonInline deferred inline selection #26002
Fix "Since 3.8.0-RC1, inline match with inlined values sometimes does not compile as it erases values that it accesses" #24935
Copy erased flag into inline access proxies #26191
Fix (#26178) private inline subclass access proxy bug #26176
Speed up inlining #26823

Java Interop

Add support for java records in pattern matching #26497
Feat: support Java 25 main class discovery #26642

JDK

Replace synchronized(this) with lock-free initState in LazyList #26100
Parse classfile generic parameters defined in supertype generic signature #26317
Handle missing Java inner class dependencies in classfile parser #26673

Standard Library

Make scala.util.ChainingOps methods inline #24725
Add an implementation of IsSeq for IArray. #24552
Add an implementation of BuildFrom for IArray #24674
Add CanEqual instance for NamedTuple #24890
Add string singleton comparison operators to scala.compiletime.ops.string. #24748
Chore: remove old support for getClass in scala.AnyVal #24687
Chore: StringContext methods are not Scala 2 macros anymore #24407
Replace runtime.Rich* implicits on primitives by direct extension methods. #23872
Add implicit conversion from IArray.type to Factory #24675
Remove all uses of String.format from the standard library. #26568
Fix Boolean scaladoc to match other primitives re: extensions #26659
Fix Enumeration.ValueSet.iteratorFrom for negative IDs #26672
Fix: LongMap.put returning None for existing Long.MinValue key #26274
Perf: fix redundant rootNode.diff computation in HashSet.diff #26275
Perf: eliminate redundant getHash calls in HashMap/HashSet concat #26278
Perf: skip builder allocation for empty source in HashMap.from #26280
Perf: eliminate local object allocation in RedBlackTree.partitionEntries #26285
Perf: ArrayDeque.clear() from O(n) to O(1) with GC-safe nulling #26288
Perf: use bound variable in ArrayOps.WithFilter.flatMap #26294

Linting

Fix "Spurious shadowing warning with -Wshadow:type-parameter-shadow" #26566
Fix false unused for renamed extension method #26441
Add warning for use of interpolator from Any #26305
Update -Wconf:src to match Scala 2 behavior #24772

Match Types

Fixes #26683: Do not answer IsConst for a stuck match type #26685
fix: #25843 Don't add capture sets to MatchCase type encodings #26306

Quotes

Recover call skolems in avoid instead of typing inline proxies as skolem #26872
fix: #25245 Ensure remapping of class member infos referencing spliced types #26307
Check macro expansion type #25756
Macro interpreter: rethrow RecursionOverflow #26896

Nullability

Make stableNull public in the stdlib #25886
Make Null a subclass of AnyVal under -Yexplicit-nulls. #25393
Safe universal methods under -Yexplicit-nulls. #26771

Parser

Fix #26564: warn on dubious negative Long/Float/Double literal syntax #26725
Parser: Recover from unclosed string literal errors #26763
Fix outline compilation with string interpolation #26636
Make with type operator an error #26545
Dedented string literals alternative implementation #26332
Support \s space escape also in interpolations #26845

Pattern Matching

Fix false exhaustivity warning on invariant type constructors #26430
Simplify unapply result types to handle match types #26631
Check inhabitedness of counter-examples in satisfiable #26356
Preserve refinement types in SpaceEngine's erase #26403
Ignore classifiers when casting in a pattern match #26526
Extend checkSensical test to scrutinees of derived value classes #26421
Handle generic tuple in getMatch branch #26157

Pickling

Fixes #25947, #11043: Avoid JavaArrayType in synthesized classOf for structural calls #26028
Stop emitting SourceFile annotation #26437

Presentation Compiler

Fix build break due to conflicting PRs #26495
Improvement: fallback PC symbol location position to a classfile if no source exists #26454
Fix PcInlayHints crash on inlined trees from external dependencies #26385
Bugfix: Don't show errors from other files #26346
Chore: Add batch semanticdb for Metals 2 #26323

REPL

Feat: add -Yrepl-print-tostring to render REPL results via toString #26435
Feat(repl): support the toolkit directive and :toolkit command #26788
Retain loading diagnostics across REPL completions #26818
Fix(repl): restore SourceFile.maybeIncomplete #26811
Drop REPL parse warnings on parse error #26798
Feat(repl): support the jar directive #26726
Feat(repl): support dependency directive aliases #26722
Refactor(repl): command registry #26716
Refactor(repl): using directive handling #26708
REPL: refactor parsing commands + trailing code + extra test coverage #26602
Fix: REPL crash on :dep after compiler queries #26599
REPL: apply settings changes to trailing code #26596
Prevent mixing of : commands and //> using directives in a single REPL input & raise directives parser diagnostics #26592
Fix: rollback REPL state after compilation error #26536
Allow for directives in the REPL to be preceded/interjected by comments or empty lines #26511
Add :replay command to the REPL #26506
Add deprecated :paste command to the REPL #26496
Feat: add :save command to the REPL #26493
Feat: -deprecation and -feature by default in the REPL #26484
Fix: make REPL completion interruptible #26443

Reporting

More helpful implicit not found message for ClassTag[T] #26715
Scaladoc: do not warn on unused scalacOptions by default #26717
Print right-associative operators as selections #26452
Expose inline call-site chain as structured DiagnosticRelatedInformation #26338
Better transparent inline errors (add note about transparent inline limitation) #26335
Fix: emit -Winfer-union warning in the REPL #26537
Do not eagerly compute potential migration diagnostic messages #26687

Rewrites

Add -Yapp-to-main rewrite converting object extends App to an explicit main #26370

SBT Bridge

Fix pattern-match undercompilation when a case class or extractor changes #26262

Scala-JS

Fixes #25792: String.split(Char) stops delegating to Regex #26036

SemanticDB

Bugfix: Fix the issue and no longer show <?> which is invalid #26607
Move test-only SemanticDB code to test sources #26482
Emit definition occurrence for primary constructor parameters in SemanticDB #26410
Semanticdb: emit occurrence for generated main entry points #26354

Transform

Emit synchronized methods explicitly on the JVM #26697
Restrict private access assert to nonsynthetic pos #26760
Fixes #26352: Reconstruct a nested module's outer accessor for inlined references in downstream units #26353
Fix SAM conversion crash on @VarArgs trait method #26141

Tuples

Make -> sugar an inline method #24728
Add support for member selection on generic tuples with abstract type bounds #26494

Typer

Prohibit Unsafe Wildcard Match-type Applications #25885
Allow appliedToTypeTrees to operate on block expressions #26259
Fixes #24936: "missing outer accessor" crash for static module reached via trait self type #26355
Fixes #24414: Fix StaleSymbolException in Namer.addChild after compilation suspension #26019
Do not create forwarders when an error has already occurred #26220
Fix stable reference check for And types with type params #25940
One more fuel check #26897

Experimental: Capture Checking

Fix capture checker crash when mapping a Var capture set #26667
Fixes #26556: Handle flexible types in cc #26709
Do Not Map Capture Variables in GlobalCapToLocal #26581
Prohibit capset applications with postfix hat #26583
Be more selective in localCapToGlobal #26453
Tests for #26416 #26423
Disallow polymorphic function types over impure function types #26084
Changes to usage leak detection and reporting #26253
Add missing & caps.Pure bounds to the ClassTagSeqFactory family #26224
Several fixes around fresh and Unscoped. #26193
Keep parameter names of closures under cc #26315
CC: Implement Classifier Exclusion Pt. 1 & 2 #26383
Add MutableIdentitySet to optimize variable dependencies in CC #26720
Some small fix in CC #26705
Fix empty capture set handling in CC Setup #26519
Better handling of nested capture sets #26547
Drop reach capabilities #26246

Coverage

Fix coverage capture for lifted constructor args #26571
Fix coverage lifting of skolem-prefixed types #26613
Scoverage: instrument chained calls correctly #26166
Fix coverage lifting across unsafeDiscardUses #26601

Experimental: Erased definitions

Erased vars #26134
Simplify erased parameters #26396
Mark erased as always used #26729

Experimental: Match Subcases

Improve exhaustivity/reachability checking for sub-cases #25694

Experimental: Separation Checking

Handle method application in separation checker #26419
Fixes for pattern matching under separation checking #26580

Experimental: Strict Equality

Enable strictEqualityPatternMatching (SIP-67) by default & add deprecation mechanics for -language feature flags #26424
Fix experimental flags for SIP-67 to be enabled at Scala 3.10 #26428

Experimental: Unroll

Make unroll a preview feature #24903

JVM Backend Optimizer

Use the optimizer on the bootstrapped compiler #26373
Stop capturing a Context for optimizer warnings #26236
Optimizer misc improvements #26704
Only run trait specialization passes when compilation units contain inline traits #26842

Named Tuples

Optimise NamedTuple.toSeqMap #25318
Make namedTupleCanEqual stable #26243
Fix NamedTuple scaladoc #26319
Fix named-tuple pattern resolution under -Yexplicit-nulls #26233

Package Manager

Add deb and rpm packaging #26858

Settings

Remove deprecated settings lifted to other categories #26170
Remove no-op deprecated settings #26171
Remove deprecated -Youtput-only-tasty #26169
Add back and deprecate already stabilised/in-preview language feature flags #26425
Move relaxedLambdaSyntax from experimental to preview #26728

Specification

Preview SIP 68: Referenceable package objects #24586

Testing

Add DeterminismTest checking classfile/TASTy stability under recompilation #26553

Infrastructure

Use the stdlib more instead of defining methods in dotc.util #24724
Simplify classpath handling #26313
Centralize JAR handling #26331
Encapsulate and simplify IO package further #26485
Simplify SourceFile, remove undocumented support for shebang #26444
Simplify classfile reading #26481
Improve IO package encapsulation #26398
Encapsulate source paths more #26795
LogicalPackagesProvider: use the compilation Context #26776
Fix paths of binary dependencies on module objects #26761
Remove NoAbstractFile #26706
Remove misleading Symbol.isPrivate #26640
Delete dead code #26227
Fix some typos #26230
Remove some unneeded null checks and uncheckedNNs #26225
Tolerate lack of source file for relative paths #26900
Fix typos across the codebase #26334
Encapsulate SourceFile more #26718
Delete dead code in io #26179

Experimetnal: Safe Mode

Revise SafeRefs checking to make it work for inlined defs #26154
Disallow dollars in names in safe mode #25657

Contributors

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

According to git shortlog -sn --no-merges 3.9.0..3.10.0-RC1 these are:

   135	Solal Pirelli
    74	Martin Odersky
    29	Piotr Chabelski
    26	Oliver Bračevac
    22	Jakub Warchoł
    22	Jamie Thompson
    19	Wojciech Mazur
    16	Patryk Zieliński
    14	Anatolii Kmetiuk
    14	Rikito Taniguchi
    13	Bill Venners
    11	Sébastien Doeraene
    10	Som Snytt
     8	He-Pin(kerr)
     8	dependabot[bot]
     7	Matt Bovel
     6	Oron Port
     5	Bartłomiej Kozak
     5	Claude
     5	HarrisL2
     5	Jan Chyb
     5	Jozef Koval
     5	Lukas Rytz
     5	Tomasz Godzik
     5	Yichen Xu
     5	noti0na1
     4	Jeon Yoonjae
     4	Puerco
     2	Alex Archambault
     2	Dmytro Mitin
     2	Emil Ejbyfeldt
     2	GitHub Copilot
     2	Hamish Starling
     2	Hamza Remmal
     2	Matthias Kurz
     2	Seth Tisue
     2	Yoonjae Jeon
     1	Arnout Engelen
     1	Darwin Morris
     1	Guillaume Martres
     1	Hamish
     1	Jack Koenig
     1	Jason Zaugg
     1	Katarzyna Marek
     1	Kenji Yoshida
     1	Li Haoyi
     1	Mathias
     1	Mikołaj Fornal
     1	Piotr Paradziński
     1	Rok Kralj
     1	Stas Shevchenko
     1	Tom Riddle
     1	Walter Tetzner
     1	Zieliński Patryk
     1	eugene yokota
     1	rochala

scala/scala3 3.10.0-RC1 on GitHub

Breaking changes

Highlights of the release

Other changes and fixes

Annotations

Backend

Desugaring

Scaladoc

Documentation

Extension Methods

Implicits

Incremental Compilation

Inline

Java Interop

JDK

Standard Library

Linting

Match Types

Quotes

Nullability

Parser

Pattern Matching

Pickling

Presentation Compiler

REPL

Reporting

Rewrites

SBT Bridge

Scala-JS

SemanticDB

Transform

Tuples

Typer

Experimental: Capture Checking

Coverage

Experimental: Erased definitions

Experimental: Match Subcases

Experimental: Separation Checking

Experimental: Strict Equality

Experimental: Unroll

JVM Backend Optimizer

Named Tuples

Package Manager

Settings

Specification

Testing

Infrastructure

Experimetnal: Safe Mode

Contributors

scala/scala3 3.10.0-RC1
on GitHub