Scala Changelog

What's new in Scala 3.4.2 RC 1

May 2, 2024

Highlights of the release:
Bump JLine 3.19.0 -> 3.24.1 & sbt 1.9.7 -> 1.9.9 #19744
Refactor settings & improve dx #19766
Publish scala2-library-tasty-experimental #19588
Repl - method signatures in autocomplete #19917
Other changes and fixes:
Annotations:
Attempt implicit search for old style implicit parameters in Application matchArgs #19737
Backend:
Fix(#17255): cannot find Scala companion module from Java #19773
Change isStatic to isStaticOwner in hasLocalInstantiation #19803
Coverage:
Port coverage filter options for packages and files #19727
Default parameters:
Lift all non trivial prefixes for default parameters #19739
Doctool:
Prevent HTML/XSS Injection in Scala Search #19980
Parse search query param in Scaladoc #19669
Experimental: Capture Checking:
Disallow covariant caps in the lower bound of type members #19624
Ignore orphan parameters inside a retains annotation during Ycheck #19684
Fix the pickling of This inside capture sets #19797
Add updated to SeqViewOps #19798
Fix Function tree copier #19822
Drop FreeSeqFactory from stdlib-cc #19849
Fix i19859 #19860
Various fixes to stdlib-cc #19873
Add more methods in SeqViewOps #19993
Check This references in refersToParamOf #20005
Exports:
Fix the tparam bounds of exported inherited classes #18647
Implicits:
Prefer extensions over conversions for member selection #19717
Don't allow implicit conversions on prefixes of type selections #19934
Make sure typeParams returns a stable result even in the presence of completions #19974
Incremental Compilation:
Fix undercompilation upon ctor change #19911
Load but not enter case accessors fields in Scala2Unpickler #19926
Initialization:
Add supports for type cast and filtering type for field and method owner in global initialization checker #19612
Added a second trace for global init checker showing creation of mutable fields #19996
Suppressing repetitive warnings in the global initialization checker #19898
Inline:
Specialized retained inline FunctionN apply methods #19801
Avoid crash after StopMacroExpansion #19883
Check deprecation of inline methods #19914
Inline transparent implicit parameters when typing Unapply trees #19646
Restore pre-3.3.2 behavior of inline implicit def #19877
Match Types:
Cover patterns using reflect.TypeTest in isMatchTypeShaped #19923
Rework MatchType recursion in collectParts #19867
Nullability:
Fix #19808: Don't force to compute the owner of a symbol when there is no denotation #19813
Parser:
Add support for JEP-409 (sealed classes) + Add javacOpt directive #19080
Fix(#16458): regression in xml syntax parsing #19522
Fix parsing of conditional expressions in parentheses #19985
Presentation Compiler:
Allow range selection on function parameter to select a parameter list #19777
Quotes:
Disallow ill-staged references to local classes #19869
Add regression test for #19909 #19915
Detect non Expr[..] splice patterns #19944
Avoid spurious val binding in quote pattern #19948
Add regression test and imporve -Xprint-suspension message #19688
REPL:
Repl truncation copes with null #17336
Catch stackoverflow errors in the highlighter #19836
Fix a REPL bad symbolic reference #19786
Reflection:
Fix TypeTreeTypeTest to not match TypeBoundsTrees #19485
Improve message when tree cannot be shown as source #19906
Fix #19732: quotes.reflect.Ref incorrectly casting This to RefTree #19930
Add check for parents in Quotes (#19842) #19870
Reporting:
Improve error reporting for missing members #19800
Avoid repetitions in name hints #19975
Improve error message when using experimental definitions #19782
Make -Xprompt work as desired under -Werror #19765
Fix #19402: emit proper error in absence of using in given definitions #19714
Bugfix: Choose correct signature is signatureHelp for overloaded methods #19707
Unify completion pos usage, fix presentation compiler crash in interpolation #19614
Scaladoc:
Fix(#16610): warn ignored Scaladoc on multiple enum cases #19555
TASTy format:
Add patch for undefined behavior with object $ #19705
Fix(#19806): wrong tasty of scala module class reference #19827
Used derived types to type arguments of dependent function type #19838
Tooling:
Java TASTy: use new threadsafe writer implementation #19690
Remove -Yforce-inline-while-typing #19889
Cleanup unnecessary language flag #19865
Bugfix: Auto imports in worksheets in Scala 3 #19793
Refine behavior of -Yno-experimental #19741
Transform:
Short-circuit isCheckable with classSymbol #19634
Avoid eta-reduction of (..., f: T => R, ...) => f.apply(..) into f #19966
Tweak parameter accessor scheme #19719
Typer:
Update phrasing for NotClassType explain error message #19635
Fix java typer problems with inner class references and raw types #19747
Approximate MatchTypes with lub of case bodies, if non-recursive #19761
Revert broken changes with transparent inline #19922
Delay hard argument comparisons #20007
Fix #19607: Allow to instantiate wildcard type captures to TypeBounds. #19627
Fix #19907: Skip soft unions in widenSingle of widenInferred #19995
Fix untupling of functions in for comprehensions #19620

New in Scala 3.4.1 RC 2 (Mar 27, 2024)

New in Scala 3.4.1 RC 1 (Mar 12, 2024)

New in Scala 3.3.3 (Feb 29, 2024)

New in Scala 3.4.0 RC 4 (Feb 29, 2024)

New in Scala 2.13.13 (Feb 27, 2024)

Language:
Support binary integer literals using 0b, as in Java (#10656 by @som-snytt)
Compatibility:
TASTy reader: support Scala 3.4 (#10670 by @bishabosha)
Support certain Java libraries compiled on JDK 21 (#10675 by @SethTisue)
For JDK 22 support, upgrade to ASM 9.6 (#10576 by @Philippus)
Align with Scala 3:
Allow either -Xsource:3 (for preparing to switch to 3) or -Xsource:3-cross (for crossbuilding on 2 and 3); some existing users of -Xsource:3 should switch to -Xsource:3-cross to avoid unwanted behavior changes (#10573 by @som-snytt)
For migration to 3, accommodate case companion as function (#10648 by @som-snytt)
Scala 3 migration warning for implicits found in package prefix (#10621 by @lrytz)
Other improvements:
-Yrelease supplements -release, allows access to additional JVM packages (#10543 by @som-snytt)
Add -Xlint:named-booleans to lint unnamed boolean literal args [ci: last-only] (#10612 by @som-snytt)
Respect java.lang.Deprecated annotation even in Scala sources (#10517 by @kapunga)
Optimize tail recursion on effectively final methods even when final keyword is absent (#10629 by @som-snytt)
Add -Xlint:pattern-shadow to lint pattern varids which are backquotable (#8806 by @som-snytt)
In mixed compilation, allow Java sources to reference MODULE$ (#10644 by @som-snytt)
Scaladoc: re-align -doc-source-url behavior with 2.12 (#10581 by @lrytz)
Known issues:
When upgrading to 2.13.13, existing users of -Xsource:3 should explicitly consider switching to -Xsource:3-cross. Some behaviors of -Xsource:3 have changed, e.g. in result type inference for inherited methods; see #10573 for details
Users of sbt must upgrade to sbt 1.9.9 to use the console task to access the 2.13.13 REPL (sbt/sbt#7502); error message is NoSuchMethodError: org.jline.utils.AttributedString.fromAnsi
Regression: Scaladoc generation may fail if you are using the TASTy reader to access Scala 3 dependencies (scala/bug#12955); error message is "Unsupported Scala 3 generic tuple type"; we'll fix it in 2.13.14
Regression: on JDK 11 (but not 8 or 17 or 21), the REPL prints a harmless "illegal reflective access" warning at startup (scala/bug#12957); we'll fix it in 2.13.14

New in Scala 3.4.0 RC 2 (Jan 24, 2024)

New in Scala 3.4.0 RC 1 (Jan 19, 2024)

New in Scala 2.13.12 (Sep 11, 2023)

New in Scala 3.3.1 (Sep 8, 2023)

Highlights of the release:
Support records in JavaParsers #16762
Port JVM backend refactor from Scala 2 #15322
Other changes and fixes:
Backend:
Disallow mixins where super calls bind to vals #16908
Fix #15107: Avoid re-emitting a LineNumber after only LabelNodes. #16813
Coverage:
Fix #17042: Preserve the shape of secondary ctors in instrumentCoverage. #17111
Default parameters:
Dupe fix when finding default arg getters #17058
Documentation:
Fix: ensure syntax blocks for ebnf are marked as such #16837
Erasure:
Handle @companionClass and @companionMethod meta-annotations #17091
Extension Methods:
Support extension methods imported from different objects #17050
GADTs:
Fix tuple member selection so it works with GADT healing #16766
Fix upper bound constraints, that are higher-kinded #16744
Split out immutable GadtConstraint #16602
Implicits:
Improve subtyping check for not yet eta-expanded higher kinded types #17139
Harden tpd.Apply/TypeApply in case of errors #16887
Try to be more subtle when inferring type parameters of class parents #16896
Include P in the implicit scope of P.this.type #17088
Incremental Compilation:
Fix under-compilation when the method type in a SAM changes #16996
Infrastructure:
Set reference version to 3.3.0-RC6 #17504
Fix #17119: Download Coursier from GitHub directly #17141
Inline:
Remove NamedArg from inlined arguments #17228
Don't generate a Select for a TermRef with NoPrefix #16754
Prepare bodies of inline forwarders eagerly #16757
Do not remove inline method implementations until PruneErasedDefs #17408
Java Interop:
ClassfileParser: allow missing param names (for JDK 21) #17536
Linting:
Improve -Wunused: locals, privates with unset vars warning #16639 #17160
Fix wunused false positive when deriving alias type #17157
Port -Wnonunit-statement setting for dotty #16936
Match Types:
Normalize match type usage during implicit lookup #17457
Fix #13757: Explicitly disallow higher-kinded scrutinees of match types. #17322
Fix match type reduction with wildcard type arguments #17065
Fix check whether classtag can be generated for match types #16708
Parser:
Allow lines starting with . to fall outside previous indentation widths #17056
Pattern Matching:
Fix #11541: Specialize ClassTag[T] in exhaustivity check #17385
Check outer class prefixes in type projections when pattern matching #17136
Make unchecked cases non-@unchecked and non-unreachable #16958
Fix #16899: Better handle X instanceOf P where X is T1 | T2 #17382
Pickling:
ClassfileParser: Avoid cycle when accessing companion in inner class lookup #16882
Polyfunctions:
Fix type aliases in beta-reduction of polyfunctions #17054
Quotes:
Register paramProxy and thisProxy in Quote type #17541
Only check newVal/newMethod privateWithin on -Xcheck-macros #17437
Unencode quote and splice trees #17342
Correctly type Expr.ofTupleFromSeq for arity > 22 #17261
Use TermRef to distinguish distinct Type[T] instances #17205
Check level consistency of SingletonTypeTree as a type #17209
Fix splice type variable pattern detection #17048
Avoid creation of @SplicedType quote local refrences #17051
Dealias type references when healing types in quotes #17049
Replace quoted type variables in signature of HOAS pattern result #16951
Beta-reduce directly applied PolymorphicFunction #16623
Use Object.toString for quoted.{Expr, Type} #16663
Fix Splicer.isEscapedVariable #16838
Fix references to class members defined in quotes #17107
Handle pickled forward references in pickled expressions #16855
Fix #16615 - crashes of path dependent types in spliced Type.of #16773
Disallow local term references in staged types #16362
Refactor level checking / type healing logic #17082
Dealias quoted types when staging #17059
Fix quotes with references to path dependent types #17081
Make arguments order in quote hole deterministic #17405
Only transform the body of the quote with QuoteTransformer #17451
Place staged type captures in Quote AST #17424
Add SplicePattern AST to parse and type quote pattern splices #17396
Reflection:
Xcheck-macros: add hint when a symbol in created twice #16733
Assert that symbols created using reflect API have correct privateWithin symbols #17352
Fix reflect.LambdaType type test #16972
Improve New/Select -Ycheck message #16746
Improve error message for CyclicReference in macros #16749
Add reflect defn.FunctionClass overloads #16849
REPL:
Always load REPL classes in macros including the output directory #16866
Reporting:
Improve missing argument list error #17126
Improve implicit parameter error message with aliases #17125
Improve "constructor proxy shadows outer" handling #17154
Clarify ambiguous reference error message #16137
Hint about forbidden combination of implicit values and conversions #16735
Attach explanation message to diagnostic message #16787
Propagate implicit search errors from implicit macros #16840
Detail UnapplyInvalidReturnType error message #17167
Add way to debug -Xcheck-macros tree checking #16973
Enrich and finesse compiler crash reporting #17031
Allow @implicitNotFound messages as explanations #16893
Include top-level symbols from same file in outer ambiguity error #17033
Do not issue deprecation warnings when declaring deprecated case classes #17165
Scala-JS:
Fix #17344: Make implicit references to this above dynamic imports explicit. #17357
Fix #12621: Better error message for JS trait ctor param. #16811
Fix #16801: Handle Closure's of s.r.FunctionXXL. #16809
Fix #17549: Unify...

New in Scala 3.3.1 RC 5 (Aug 23, 2023)

New in Scala 3.3.1 RC 4 (Aug 10, 2023)

New in Scala 3.3.1 RC 3 (Jul 11, 2023)

New in Scala 3.3.1 RC 1 (Jul 5, 2023)

Highlights of the release:
Support records in JavaParsers #16762
Port JVM backend refactor from Scala 2 #15322
Backend:
Disallow mixins where super calls bind to vals #16908
Fix #15107: Avoid re-emitting a LineNumber after only LabelNodes. #16813
Coverage:
Fix #17042: Preserve the shape of secondary ctors in instrumentCoverage. #17111
Default parameters:
Dupe fix when finding default arg getters #17058
Documentation:
Fix: ensure syntax blocks for ebnf are marked as such #16837
Erasure:
Handle @companionClass and @companionMethod meta-annotations #17091
Extension Methods:
Support extension methods imported from different objects #17050
GADTs:
Fix tuple member selection so it works with GADT healing #16766
Fix upper bound constraints, that are higher-kinded #16744
Split out immutable GadtConstraint #16602
Implicits:
Improve subtyping check for not yet eta-expanded higher kinded types #17139
Harden tpd.Apply/TypeApply in case of errors #16887
Try to be more subtle when inferring type parameters of class parents #16896
Include P in the implicit scope of P.this.type #17088
Incremental Compilation:
Fix under-compilation when the method type in a SAM changes #16996
Infrastructure:
Set reference version to 3.3.0-RC6 #17504
Fix #17119: Download Coursier from GitHub directly #17141
Inline:
Remove NamedArg from inlined arguments #17228
Don't generate a Select for a TermRef with NoPrefix #16754
Prepare bodies of inline forwarders eagerly #16757
Do not remove inline method implementations until PruneErasedDefs #17408
Java Interop:
ClassfileParser: allow missing param names (for JDK 21) #17536
Linting:
Improve -Wunused: locals, privates with unset vars warning #16639 #17160
Fix wunused false positive when deriving alias type #17157
Port -Wnonunit-statement setting for dotty #16936
Match Types:
Normalize match type usage during implicit lookup #17457
Fix #13757: Explicitly disallow higher-kinded scrutinees of match types. #17322
Fix match type reduction with wildcard type arguments #17065
Fix check whether classtag can be generated for match types #16708
Parser:
Allow lines starting with . to fall outside previous indentation widths #17056
Pattern Matching:
Fix #11541: Specialize ClassTag[T] in exhaustivity check #17385
Check outer class prefixes in type projections when pattern matching #17136
Make unchecked cases non-@unchecked and non-unreachable #16958
Fix #16899: Better handle X instanceOf P where X is T1 | T2 #17382
Pickling:
ClassfileParser: Avoid cycle when accessing companion in inner class lookup #16882
Polyfunctions:
Fix type aliases in beta-reduction of polyfunctions #17054
Quotes:
Register paramProxy and thisProxy in Quote type #17541
Only check newVal/newMethod privateWithin on -Xcheck-macros #17437
Unencode quote and splice trees #17342
Correctly type Expr.ofTupleFromSeq for arity > 22 #17261
Use TermRef to distinguish distinct Type[T] instances #17205
Check level consistency of SingletonTypeTree as a type #17209
Fix splice type variable pattern detection #17048
Avoid creation of @SplicedType quote local refrences #17051
Dealias type references when healing types in quotes #17049
Replace quoted type variables in signature of HOAS pattern result #16951
Beta-reduce directly applied PolymorphicFunction #16623
Use Object.toString for quoted.{Expr, Type} #16663
Fix Splicer.isEscapedVariable #16838
Fix references to class members defined in quotes #17107
Handle pickled forward references in pickled expressions #16855
Fix #16615 - crashes of path dependent types in spliced Type.of #16773
Disallow local term references in staged types #16362
Refactor level checking / type healing logic #17082
Dealias quoted types when staging #17059
Fix quotes with references to path dependent types #17081
Make arguments order in quote hole deterministic #17405
Only transform the body of the quote with QuoteTransformer #17451
Place staged type captures in Quote AST #17424
Add SplicePattern AST to parse and type quote pattern splices #17396
Reflection:
-Xcheck-macros: add hint when a symbol in created twice #16733
Assert that symbols created using reflect API have correct privateWithin symbols #17352
Fix reflect.LambdaType type test #16972
Improve New/Select -Ycheck message #16746
Improve error message for CyclicReference in macros #16749
Add reflect defn.FunctionClass overloads #16849
REPL:
Always load REPL classes in macros including the output directory #16866
Reporting:
Improve missing argument list error #17126
Improve implicit parameter error message with aliases #17125
Improve "constructor proxy shadows outer" handling #17154
Clarify ambiguous reference error message #16137
Hint about forbidden combination of implicit values and conversions #16735
Attach explanation message to diagnostic message #16787
Propagate implicit search errors from implicit macros #16840
Detail UnapplyInvalidReturnType error message #17167
Add way to debug -Xcheck-macros tree checking #16973
Enrich and finesse compiler crash reporting #17031
Allow @implicitNotFound messages as explanations #16893
Include top-level symbols from same file in outer ambiguity error #17033
Do not issue deprecation warnings when declaring deprecated case classes #17165
Scala-JS:
Fix #17344: Make implicit references to this above dynamic imports explicit. #17357
Fix #12621: Better error message for JS trait ctor param. #16811
Fix #16801: Handle Closure's of s.r.FunctionXXL. #16809
Fix #17549: Unify...

New in Scala 2.13.11 (Jun 7, 2023)

Collections:
Faster Vector concatenation (#10159 by @ansvonwa)
New LinkedHashMap/LinkedHashSet implementation (#10221 by @liang3zy22)
Compatibility:
Support JDK 20 and 21 by upgrading to ASM 9.5 (#10363, #10184 by @Philippus)
Fix crash reading JDK 21 classfiles (#10397)
Support Java 17 sealed in Java sources and classfiles (#10348, #10105 by @som-snytt)
Support Scala 3.3 in TASTy reader (#10299 by @bishabosha)
Align with Scala 3:
Accept implicit _, implicit (x: Int) in lambdas, like Scala 3 does (#10327 by @som-snytt)
Deprecate infix type args, as they are dropped in Scala 3 (#10255 by @som-snytt)
Allow eta-expansion of methods with dependent types (#10166)
Abstract parent copy does not suspend case copy (#10085 by @som-snytt)
Don't GLB binders of type patterns, use the type directly (#10247)
Under -Xsource:3, warn that inherited members no longer take precedence over outer definitions in Scala 3 (#10220, #10339)
Under -Xsource:3, adjust 2.13.9 change to ignore override type for whitebox macro expansion (#10188 by @som-snytt)
Under -Xsource:3, use narrowest type for pt of override (#10198 by @som-snytt)
Under -Xsource:3, warn about change to parenless lambda parens (#10320 by @som-snytt)
Lints and warnings:
Lint select from Unit, or Int that incurs widening (#10372 by @som-snytt)
Lint for integral divisions that are widened to a float (#10369 by @som-snytt)
Lint if args adapted to Unit and discarded (#10150 by @som-snytt)
Warn that implicit should have explicit type (#10083 by @som-snytt)
Other notable changes:
Disallow mixins where super calls bind to vals (#10268)
Make scalac's argument-file processing more like javac's in handling spaces and line breaks (#10319 by @som-snytt)
Bump JLine and JNA versions (#10318)
Javabootclasspath supersedes jrt (#10336 by @som-snytt)
Report total errors on stderr (#10272 by @som-snytt)
Fix pathologically slow compilation of some pattern matches since 2.13.7 (#10258 by @KisaragiEffective)
Provide equals and hashCode on IterableWrapper again (fixing 2.13.9 regression) (#10205 by @som-snytt)
Improvements to -Vimplicits; errors now show complete implicit search tree (#9944 by @tribbloid)
Vprint defaults to -Vprint:typer; phases may be prefixed with ~ to mean "before and after" (#10173 by @som-snytt)

New in Scala 3.3.0 RC 6 (May 24, 2023)

New in Scala 3.3.0 RC 4 (Apr 27, 2023)

New in Scala 3.2.2 (Feb 3, 2023)

Highlights of the release:
Make truncation by characters in REPL configurable #16167
New (experimental for now) lazy vals implementation #15296
Other changes and fixes:
Coverage:
Make coverage instrumentation more robust #16235
Default parameters:
Resolve overloading: keep track of prefix and indices of all default getters #16009
Experimentals:
Let accessors inherit @experimental annotations from accessed symbols #16099
Extension Methods:
Fix i14451 #16010
GADTs:
Add fixed GADT exhaustivity test cases #16169
Eliminate class hierarchy in GadtConstraint #16194
Initialization:
Code refactoring of initialization checker #16066
Inline:
Refine checking for outer references #16122
Java interoperability:
Parse native in Java bytecode as @native #16232
Opaque Types:
Disallow opaque type aliases of context functions #16041
Overloading:
Fix curried overloading resolution for polymorphic methods #16485
Parser:
Align implementation with spec of soft modifiers #15961
Pattern Matching:
Fix redundancy (unreachability) warning #16179
Teach SpaceEngine that generic tuples are irrefutable #16051
Fix exhaustivity warning #16168
Polyfunctions:
Avoid checking purity of Apply without symbols #16221
Reporting:
Expose reason for unchecked warning #16086
Refine AsSeenFrom approximation scheme #15957
Better output under -Ydetailed-stats #15950
Fix crash in -Vprofile code #16007
Name stripped of module suffix must not be empty #15597
Fix InlineMatch pos for summonFrom #16025
Rewrites:
Rewrites are UTF-8 #15622
Scala-JS:
Fix the detection of inferred types of = js.native. #16184
Do not elide fields required for Scala.js interop semantics. #16187
Scaladoc:
Update quick links for new UI #15912
Avoid parsing code comment twice #16154
Make footer text configurable #16064
Add typography fallback fonts #16063
SemanticDB:
Emit SymbolInformation and Occurrence for anonymous class #15865
Fix regression in type apply synthetics #16031
Transform:
Fix creating forwarders for simple alias givens #16193
Only check for Scala2LocalSuffix in methods on Scala 2.x classes #16014
Fix mapping TypeMaps over annotations #15948
Peephole optimization to drop .apply from partially applied methods #16022
Typer:
Fix approximateOr of (A & Double) | Null #16241
Create boxed environments only for references and function values #16136
Fix higher-order unification incorrectly substituting tparams #16181
Handle copies of constrained type lambdas when determining an implicit scope #16159
Create message for missing arguments #16158
Make singleton types subtypes of their refined type #16135
Disallow overriding val parameters #16096
Avoid crash where creator proxies are referenced indirectly #16098
Refine estimation of default arguments in overloading resolution #15962
Harden canAssign #15963
Fix isSubType for static objects filling in type projections #15959
Fix expected type of TupleXXL unapply #16248
Drop lazy recursive application in approximateParent #16073
Type match with a match type when a match type is expected #15599
Compute completions at typerPhase #16371
Only include accessible base classes in orDominator #16477

New in Scala 3.3.0 RC 2 (Feb 3, 2023)

New in Scala 3.2.2 RC 2 (Dec 22, 2022)

New in Scala 3.2.2 RC 1 (Nov 8, 2022)

Highlights of the release:
Make truncation by characters in repl configurable #16167
New (experimental for now) lazy vals implementation #15296
Other changes and fixes:
Coverage:
Make coverage instrumentation more robust #16235
Default parameters:
Resolve overloading: keep track of prefix and indices of all default getters #16009
Experimentals:
Let accesors inherit @experimental annotations from accessed symbols #16099
Extension Methods:
Fix i14451 #16010
GADTs:
Add fixed GADT exhaustivity test cases #16169
Eliminate class hierarchy in GadtConstraint #16194
Initialization:
Code refactoring of initialization checker #16066
Inline:
Refine checking for outer references #16122
Java interoperability:
Parse native in Java bytecode as @Native #16232
Opaque Types:
Disallow opaque type aliases of context functions #16041
Parser:
Align implementation with spec of soft modifiers #15961
Pattern Matching:
Fix redundancy (unreachability) warning #16179
Polyfunctions:
Avoid checking purity of Apply without symbols #16221
Reporting:
Expose reason for unchecked warning #16086
Refine AsSeenFrom approximation scheme #15957
Better output under -Ydetailed-stats #15950
Fix crash in -Vprofile code #16007
Name stripped of module suffix must not be empty #15597
Fix InlineMatch pos for summonFrom #16025
Rewrites:
Rewrites are UTF-8 #15622
Scala-JS:
Fix the detection of inferred types of = js.native. #16184
Do not elide fields required for Scala.js interop semantics. #16187
Scaladoc:
Update quick links for new ui #15912
Avoid parsing code comment twice #16154
Make footer text configurable #16064
Add typography fallback fonts #16063
SemanticDB:
Emit SymbolInformation and Occurrence for anonymous class #15865
Fix regression in type apply synthetics #16031
Transform:
Fix creating forwarders for simple alias givens #16193
Only check for Scala2LocalSuffix in methods on Scala2x classes #16014
Fix mapping TypeMaps over annotations #15948
Peephole optimization to drop .apply from partially applied methods #16022
Typer:
Fix approximateOr of (A & Double) | Null #16241
Create boxed environments only for references and function values #16136
Fix higher-order unification incorrectly substituting tparams #16181
Handle copies of constrained type lambdas when determining an implicit scope #16159
Create message for missing arguments #16158
Make singleton types subtypes of their refined type #16135
Disallow overriding val parameters #16096
Avoid crash where creator proxies are referenced indirectly #16098
Refine estimation of default arguments in overloading resolution #15962
Harden canAssign #15963
Fix isSubType for static objects filling in type projections #15959
Fix expected type of TupleXXL unapply #16248
Drop lazy recursive application in approximateParent #16073
Type match with a match type when a match type is expected #15599

New in Scala 3.2.1 RC 4 (Oct 18, 2022)

New in Scala 3.2.1 RC2 (Oct 17, 2022)

New in Scala 2.13.10 (Oct 13, 2022)

New in Scala 2.13.9 (Sep 22, 2022)

New in Scala 3.2.1 RC1 (Sep 15, 2022)

Highlights of the release
Add experimental capture checking #15877
Scaladoc: New UI design #15697
Other changes and fixes:
Backend:
Set ACC_FINAL access flag to final variable accessors #15707
Coverage:
Avoid instrumentation of inline and erased definitions #15504
Erasure:
Fix #15199: Exclude JavaDefined Modules from bridge generation. #15499
Extension Methods:
Merge nested polytypes in more cases in resolveOverloaded #15636
GADTs:
Gix GADT casting when typing if expressions #15646
Use GADT constraints in maximiseType #15544
Add the expected type to Poly's desugaring #15570
Allow refineUsingParent to infer GADT bounds #15706
Avoid leaking internal types in GadtConstraint.approximation #15558
Improve GADT usage tracing for MatchType reduction #15872
Add gadtAddBound to ExplainingTypeComparer tracing #15819
IDE Support:
Recover from TypeErrors in isErroneous #15442
Add a guard against empty ident #15542
Initialization:
Fix #15465: Use resolveThis for outerSelect resolution #15606
Fix #15459: Display uninitialized fields in promotion error #15488
Fix #15363: Improve error messages for leaking of this #15364
Make sure inner classes are checked first #15527
Handle super accessors in initialization checker #15703
Inline:
Check is inline unapply has leading implicits #15583
Fix #15374: Make sure prefix of outer select has the correct class symbol #15592
Java Interoperability:
Don't check import selectors for Java code #15617
JS Interoperability:
Fix #15701: Implement js.dynamicImport for dynamic module loading. #15720
Implement support for js.new.target. #15734
Fix #14488: Scala.js: Add compiler support for scala.Enumeration. #15770
Match Types:
Avoid null types when reducing match types #15748
Avoid references to unbound parameters in applied type patterns #15710
Nullability:
Fix checking ctx to carry correct modes #15350
Pattern Matching:
Teach provablyDisjoint to handle FromJavaObject #15769
Don't trust case class extractors with explicit type arguments #15669
Space: Fix how sealed abstract classes decompose #15553
Local classes are uncheckable (type tests) #15134
Fix ValDef span assignment in PatternMatcher #15783
Reject all explicitly written type references with bad bounds #15577
Pickling:
Make simplify replace type parameters inside method types #15430
Quotes:
Ignore types in macro runtime dependencies #15529
REPL:
ReplDriver.run and :load take complete input #15811
REPL goes through a phase #15663
Avoid assertion failure for illegal trait inheritance #15631
Reporting
Underline assignment correctly in error message #15584
Better error message for "implicit search must be more specific" #15747
Provide better info on compiler crashes #15890
SemanticDB:
Handle colons in file names when producing SemanticDB #15863
Standard Library:
Fix throwReturn of NonLocalReturns to allow wider usage #15495
Tooling:
Fix scala runner exit codes #15604
Command line parser respects outer escaped quote #15497
Added quotes to Scala home paths in scala and scalac scripts #15824
Retain partial type params typying information on error #15825
Transform:
Implementation restriction: No partial functions with CFT results #15744
Fix treatment of parameter selections via this in constructors. #15737
Fix expansion and unexpansion of mixin qualified names #15712
Fix #15514 in Parser #15524
Check type arguments for bad bounds #15571
Typer:
Fix swapKey #15894
Insert GADT casts for needy match types #15851
Add missing dealias in isContextFunctionRef #15742
Look for synthetic applies also under type applications #15572
Optimize isSameType for invariant applied types with the same structure #15556
Fix cycle detection for type aliases with wildcard arguments #15508
Handle recursions in isFullyDefined #15443
Do level checking on instantiation #15746
Use fullyDefinedType for mirror synthesis #15814
Instantiate more type variables to hard unions #15632
Simplify level fixing scheme #15936
Don't normalize in AppliedType#superType #15453
Try promotion while widening arguments #15467
Check import selectors at Typer #15477
Turn some calls to underlying into superType. #15455
Find more looping implicits #15481
Fix findFunctionType for OrTypes #15478
Fix looping implicits check #15655
Try to avoid static symbols if leaving them would make a leak #15548
Do not fold IsConst applied to dependent parameters #15759

New in Scala 3.2.1 RC1 (Sep 15, 2022)

New in Scala 3.2.0 (Sep 5, 2022)

New in Scala 3.2.0 RC3 (Aug 18, 2022)

New in Scala 3.2.0 RC2 (Jul 8, 2022)

New in Scala 3.2.0 RC1 (Jun 21, 2022)

Highlights of the release:
Add runtime.TupleMirror to avoid anonymous classes for mirrors of tuples #15404
Fix TupleXXL.productPrefix #15411
Synthesize mirrors for small generic tuples #15250
Fix #14150: Constrain refinements to type parameters #15014
Gradual warning for deprecated nonlocal return #15303
Restrict mirrors of any union type #15279
Stabilize 3.2 APIs #15197
Add error reporting for mirror synthesis #15164
Fix #14432: Check if scala 2 case class is accessible #15008
Fix #12919: Summon anonymous mirror when companion is a case object #14986
Erase Int | Nothing signatures types into Int #14971
Allow exports in extension clauses #14497
Fix Scala Wart about implicit () class parameters #14840
Re-architecture quote pickling #12540
Add scala.annotation.MainAnnotation #14558
Add in initial support for code coverage #13880
Support tuple specialisation #15060
Remove support for -scala-output-version flag #15146
Make lazy vals and object native image friendly #14780
Allow return in tailrec position #14067
Other changes and fixes:
Backend:
Keep annotation order #15063
Update asm to 9.3 #14926
Fix #14773: Reuse the param slots for the tailrec local mutable vars. #14865
Better error messages in case of TooLarge* exceptions in GenBCode #14943
Coverage:
Fix relativizing paths in coverage serializer #15240
Erasure:
Handle & and | types when computing tuple arity #15330
Experimentals:
Fix check experimental inline references #15147
Exports:
Refine criterion when to skip identifiers in pattern constructors #15367
Simplify and harden duplicates checking in exports #14879
Fix isAbsType prediction in TreeUnpickler #14861
F-bounds:
Recursion brake for joins in TypeComparer #14880
GADTs:
Heal pattern-bound type by gathering constraints #15095
Consider GADT upper bounds when upcasting the scrutinee type #15351
Extract wildcard GADT constraints more directly #14832
IDE Support:
Docs: Add a comment to pathTo mentioning that it might return errorTermTree #15420
Fix completions to properly contain public fields if they were shadowed #15236
Add proper signatureHelp for unapply methods #15203
Fix signatureHelp to show enclosing apply instead of closest one. #15119
Fix implicit conversion type resolve in completions #15061
Fix type alias completion, unify completion tests style #15047
Support code completion for refined types #15283
Fix SourceFile.column method. #15209
Initialization:
Check method arguments with parametricity when static #14916
Add safe-init test to prevent adding cold elements to hot arrays #14895
Allow non-hot values in SeqLiterals #14794
Inline:
Make private inline accessors final #15324
Fix inlining when outer select is needed from inline call prefix #15327
Support inline methods calling private inline methods on this #15075
Types with only an abstract inline method are not SAMs #14874
Don't issue unreachable error messages for inlined code #14871
Dealias arg type to detect opaque types #15074
Fix dependency status calculation for refined type aliases in method result types #15390
Java Compatibility:
Java generic signatures can't refer to type members #15093
Simplify and correctify calculation of the InnerClass attribute #15153
Fix #13523: Survive missing Java inner annotation classfiles #15094
Match Types:
Implement provablyDisjoint for refined types and type aliases #15375
Cache skolem types #14909
Nullability:
Speed up .nn #15418
Fix handling imports in TreeUnpickler #15137
Honor language imports when unpickling #14962
Remove special eq/ne in unsafeNulls #15186
Add eq/ne extension for AnyRef|Null to Scala3RunTime #14632
Parser:
Fix parser error for type arguments with trailing comma #15395
Change fewerbraces to always use a colon, even before lambdas #15273
Deprecate 3.1-migration, err on import #14978
Treat all incomplete ifs as statements #14960
Clarify and test rules for newline suppression #14877
Tweak assertion in withMods #14857
Fix loop in parser #15421
Parse unary operators as regular identifiers when backquoted #15198
Pattern Matching:
Preserve modifiers when desugaring for-comps #15403
Extract unapply types like typedUnApply #15254
Force Java enum children to be queried #15109
Enable stricter pattern binding warnings by default #14294
Pickling
Survive unpickling crashes when completing from Tasty #14884
Quotes:
Transform RHS of captured assignment reference #15247
Properly look for inline methods #15072
Fix hash code of ExprImpl and TypeImpl #15281
Compute correct argument type in ExprMap #15269
Detect quoted pattern variables in alternatives #15073
Disallow old uses of quoted and spliced types #15012
Fix capturing conditions of HOAS quote patterns #14822
Reflection:
Add missing cases in SourceCode printer #15032
Add reflect AppliedType constructor #14923
Add regression test #14924
Reporting:
Case class must have at least one leading non-implicit parameter list #15382
Improve opaque type with no RHS error message #15285
Refine condition when to report errors in an inserted apply #15016
Accept soft modifiers separated by blank lines #14959
Fix warning with leaking this into Scala2 synthetic apply #15307
Refine error messages for early promotion #15263
Standardize -rewrite advertisements and suppress them in REPL #14955
Improve diagnostic for refutable extractors in pattern bindings #14988
Fix: correction to ClassTooLargeException message #14974
Scaladoc:
Fix rendering ThisType #15440
Add extension suffixes and fqName to scaladoc searchbar #15048
Fix implicit members resolution #15021
Fix windows paths handling in legacy external link provider #15023
Warn about special characters in filenames according to the default Jekyll rules #14657
Scaladoc annotations rework #15361
Fix expanding docstrings in Scaladoc #15045
Scripting:
Fix #13760: Running script compiled jar no longer restricted to java.base module #15103
SemanticDB:
Do not register SymbolOccurrence for non-symbol endmarker #15143
Standard Library:
Implement new main annotation #14841
Add compiletime.ops.string.CharAt #14431
Make EmptyTuple a case object #14972
Tasty Inspector:
Handle this prefix in classes (in quote patterns) #14800
Fix parameter untupling #14816
Tooling:
Add -Vprofile option #15406
Fix rewrite for type-ascribed refutable pattern binding #15314
Fix rewrites for refutable pattern bindings #14954
Transform:
Also hoist lifted arguments in super calls #14919
Add deprecated overriding checks #15432
Don't cast to a value class as self type #14885
Disallow @targetName on top-level class, trait, and object #15068
Handle case where abstract overrides miss an implementation #14893
Treat RecTypes as potentially uncheckable #14894
Allow multiple wildcard vals #14906
Typeclass Derivation:
Support intersection types in mirrorCompanionRef #15192
Fix #15222: Recursively check for product ctor accessibility #15231
Fix 14025: Restrict curried type lambdas in mirror generation #15006
Make anonymous mirrors serializable #15391
Typer:
Fix #15405: Dealias Or type constituents when finding its dominator #15416
Handle unconstrained TypeVars when synthesizing ClassTags #15376
Allow for unqualified apply as context functions #15417
Prevent crash when reporting an error #15320
Show a match type trace for "not a class type" errors #15218
Don't constrain type variables in normalize #15223
Eta expand CFTs in super accessors if needed #15092
Reject structural applications of polymorphic methods #15090
Hande clashes between same-named exports #14967
Fix outer reference detection in class parents #14961
Avoid redundant type test for irrefutable @unchecked patterns #14898
Detect clashes involving renamed exports #14831
Guard against stackoverflows when instantiating HK-Lambdas #14851
Don't try conversions or extensions on Java companion objects #14881
Revert #14452 and make compile-time operations on stable arguments stable #15268
Better handling of type parameters in constructor pattern #15356
Handle AvoidMap recursions #15393
Add missing condition in checking synthetic apply #15362
Harden type assignment of lambda trees #14887
Disallow package names as types #14888
Fix constToLiteral #14853

New in Scala 3.1.3 (Jun 21, 2022)

Highlights of the release:
f-interpolator: Scala 2 parity and bugfixes #13367
Show inlined positions with source code on errors #14002
Add reflect ClassDef.apply and Symbol.newClass #14124
Add experimental TupledFunction #14414
Other changes and fixes:
Backend:
Filter out static forwarders for Java package private methods #14662
Emit all classes as public to avoid object deserialization issues #14686
Upgrade to ASM 9.2 #14711
Desugaring:
Adapt function arguments to n-ary prototype #14651
Erasure:
Don't optimize explicitly written isInstanceOf tests away. #14715
Exports:
Fix use of exported prefix #14461
Export constructor proxies for parameterized classes #14681
GADT:
Fix #14726: call exclusiveLower before addLess during unification #14727
Avoid unsound GADT constraints derived from subtyping relations between singletons and refined types #14728
Keep correct kind when preparing constraint in stripParams #14761
Initialization:
Add special case to init checker to always allow certain methods #14352
Implicits:
Avoid unnecessary under-constrained implicit searches #14353
Prevent implicit conversion chaining #14750
Fix hasKnownMembers #14762
Match types:
Fix #13855: Chaining Match Types fails at value level #14354
Constrain pattern types when typing a match type case #14563
Fix bounds of match type cases #14645
More aggressive reduction of type selection (fixes parboiled2) #14987
Relax avoidance checks more for match type reduction #15036
Re-establish missing symbol from previous phase (in one specific case) #15295
Metaprogramming:
Allow nested Quotes with a different owners #13652
Add typed versions of Mirror.ProductOf#fromProduct #14114
Fix #14393: foldOver in default TreeAccumulator can't process Typed nodes #14396
Fix invariant quote type holes #14425
Make singleton operations covariant #14452
Find inline calls inserted in synthetic members #14480
Don't generate Mirror.Sum for simple enum cases #14525
Collect all local class definitions #14528
Only make the staged parts of a quote inlineable #14604
Tolerate some faults when copying trees in InlineTreeMap #14674
Handle this prefix in objects (in quote patterns) #14732
Detect when position is not in known source #14801
Handle SummonFrom in reflect TreeAccumulator #14809
Handle situation where an inline info cannot be computed #14827
Opaque Types:
Disallow overriding opaque type aliases #14665
Disallow private opaque type aliases #14666
Generate opaque proxies also for base classes #14668
Parser:
Accept supplementary Unicode characters #13136
Don't compute indents when in a string #14441
Parse empty arguments in (invalid) Apply more often #14463
Expand span errorTermTree to include skipped span. #14492
Fix lookahead logic in Scanner #14562
Add private inteface methods parsing in JavaParser #14643
Reject postfix ops already in Parser #14677
Syntax error recovery #14695
Pattern matching:
For generic tuples, call Tuples.apply instead of _1/_2/.. #14296
Preserve the intersection of disjoint numbers in match analysis #14550
Fix casting of generic tuple selection #14590
Ignore private/sealed abstract class/traits #14599
Drop special treatment for Scala-2 code in unapply #14766
Pickling:
Disable type simplify in unpickler #14506
Check if package names will be encoded in desugar #14597
Fix picking default syntax for comments #14725
Fix lack of type avoidance in argument lifting #15229
Refchecks:
Don't skip override tests when overridden is AbsOverride #14527
Extend "cannot override mutable variable" restriction to deferred var… #14724
Repl:
Avoid stale import context during REPL parsing #14493
Fix #11202: Incorrect highlight for type constructor #14518
Make empty catch an incomplete. #14519
Add in feedback when resetting REPL state #14521
Fix #14535: End marker now has the same color as its definition in repl #14555
Add backticks when needed in completions #14594
Autocomplete repl commands #14627
Harden REPL in presence of values that fail to initialize #14702
Reporting:
Change error message text from "fully-initialized" to "fully initialized" #14400
Improve -explain rendering #14357
Propagate unreported features when flushing a reporter #14503
Avoid using · character #14453
Fix explain rendering with Windows EOL #14456
Fix #14576: Ensure unreported warning summaries are also emitted via sbt-bridge #14602
Add context to safe-init warnings for inlined methods #14646
Show unique ids of pattern bound symbols #14716
Don't replace typevars by their f-bounds in error messages #14723
Error message improvement for illegal access extension methods #14730
Warn on misleading indentation in single-case catch #14738
Use correct ErrorMessageID for EmptyCatchOrFinallyBlock #14786
Correct highlight interpolation in explain message #14802
Don't issue implicit errors if parameter has default value #14849
Typer:
Fix approximating RefinedTypes (n>1) #14361
Allow override protected[C] in companion #14105
Hide apply generated for rotected case class constructor #14266
Infer parameters of eta applications with vararg parameters #14397
Keep softness when widening unions #14399
Fix #11008: Support generic tuples as a valid unapply result #14434
Fix TreeTypeMap to correctly substitute type parameters #14537
Handle ownership changes in InlineTyper #14568
Handle more corner cases in etaReduce #14628
Remove false unchecked warnings on refined types #14703
Fix hoisting local symbols #14714
Fix desugaring empty argument blocks in normArgs #14719
Improve overloading resolution if expected type is not FunProto #14733
Don't force LazyRefs when computing DepStatus #14774
Avoid NPE in simplify #15310
Eta expand export forwarders that have context function types #15217
Partially revert #14026 - Fixes 4 regressions #15343
Explicit nulls:
Fix override containing type param #13975
Fix case null on non-nullable type in unsafe null #13976
Thread context through block in transforms correctly and efficiently #14523
Fix intercept TypeApply #14617
Fix #14682: fix overriding check in mergeSingleDenot #14755
IDE Support:
Fix contextOfPath for Template #12783
Search all source trees for a given span #14436
Set zero span for synthetic enum import selector #14498
Set zero span for synthetic tuple type #14499
Set proper position for ValDefs generated from tuples #14513
Provide signature help for unapply methods #14611
Add completions for specific MatchType cases #14639
Support backticked imports in completions #14649
Change completions filtering to now include package module classes #14756
Scaladoc:
Correctly handle context functions #14371
Fix rendering dependent function types #14327
Unescaped special characters in Quotes documentation #14377
Refactor static site loading and directory structure #14378
Make member filtering case-insensitive #14430
Add member position IDs to anchors in searchbar #14454
Repair links #14475
Follow renames in content contributors script #14478
Change default blog directory to blog #14485
Refactor generation configuration in sbt. Generate reference documentation using Scaladoc #14489
Fix issues with incorrect external links and special characters #14516
Grouping entries in searchbar. Add hints to searchbar #14539
Fix #14481: certain functions not being shown in searchbar #14546
Fix function classpathArgs() #14559
Add necessary parentheses in function types #14565
Fix groupping entries using markdown syntax #14577
Add table of content to static sites #14607
Allow to set a comment syntax based on path to source #14650
Tweak Language Reference documentation #14669
Don't add extra newlines when there aren't extra sections in doc markdown #14734
Fix regression with extension methods not being shown in searchbar #14779
Fix snippets hiding and buttons animation #14839
SemanticDB:
Update generated semanticdb code with the latest scalapb #14591
Support MatchType#14608
Other:
Kotlin interop: Find nested class if InnerClass entry is missing #14426
Add 3.2 language mode internally, treat it like 3.0, 3.1 #14690
Add -h to alternatives for -help #14792
Avoid overeager completion of Java annotations in classfile parser #15185
Implement scalac script in Scala #15212
Fix #15220: Windows scripts do not delegate to MainGenericRunner #15325

New in Scala 2.13.8 (Jan 13, 2022)

New in Scala 2.13.7 (Nov 1, 2021)

New in Scala 2.13.6 (May 18, 2021)

New in Scala 2.13.5 (Feb 23, 2021)

New in Scala 2.13.4 (Nov 19, 2020)

New in Scala 2.13.3 (Jun 25, 2020)

New in Scala 2.13.2 (Apr 23, 2020)

New in Scala 2.13.1 (Sep 18, 2019)

New in Scala 2.13.0 (Jun 11, 2019)

Release summary:
2.13 improves Scala in the following areas:
Collections: Standard library collections have been overhauled for simplicity, performance, and safety. This is the centerpiece of the release.
Standard library: Future is faster and more robust. Elsewhere, useful classes and methods have been added.
Language: Literal types, partial unification, by-name implicits, more.
Compiler: 5-10% faster, deterministic output, improved optimizer.
Collections redesign:
Standard library collections have been overhauled for for simplicity, performance, and safety.
This is the centerpiece of the release.
Most ordinary code that used the old collections will continue to work as-is, except as detailed below.
The most important collections changes are:
Simpler method signatures
No more CanBuildFrom. Transformation methods no longer take an implicit CanBuildFrom parameter.
The resulting library is easier to understand (in code, Scaladoc, and IDE code completion).
It also makes user code compile faster.
A new BuildFrom implicit is used in a handful of places that need it.
Simpler type hierarchy
No more Traversable and TraversableOnce.
They remain only as deprecated aliases for Iterable and IterableOnce.
Parallel collections are now a separate module.
As a result, GenSeq, GenTraversableOnce, et al are gone.
Immutable scala.Seq
Seq is now an alias for collection.immutable.Seq
Before, it was an alias for the possibly-mutable collection.Seq.
This also changes the type of varargs in methods and pattern matches.
Arrays passed as varargs are defensively copied. (#6970)
Simplified views that work
collection.Views have been vastly simplified and should now work reliably.
New, faster HashMap/Set implementations
Both immutable (d5ae93e) and mutable (#7348) versions were completely replaced.
They substantially outperform the old implementations in most scenarios.
The mutable versions now perform on par with the Java standard library's implementations.
New concrete collections
immutable.LazyList replaces immutable.Stream. Stream had different laziness behavior and is now deprecated. (#7558, #7000)
immutable.ArraySeq is an immutable wrapper for an array; there is also a mutable version
mutable.CollisionProofHashMap guards against denial-of-service attacks (#7633)
mutable.ArrayDeque is a double-ended queue that internally uses a resizable circular buffer (scala/collection-strawman#490)
New abstract collection type SeqMap
immutable.SeqMap provides immutable maps that maintain insertion order. (#7954)
Implementations: VectorMap (#6854) and TreeSeqMap (#7146) (in addition to the already existing ListMap).
Additional collections changes:
New to(Collection) method
Replaces old to[Collection] method.
The argument is the companion object of the desired collection type, for example .to(Vector).
The API change enables support for all collection types (including Map, BitSet, et al).
No more collection.breakOut
It required CanBuildFrom, which no longer exists.
To avoid constructing intermediate collections, use .view and .to(Collection) instead.
List and Vector are safer
They now offer safe publication under the Java Memory Model, using releaseFence (#6425)
Java interop has moved
Extension methods for Scala are now in scala.jdk
Explicit converters for Java are in scala.jdk.javaapi
The reorganization centralizes all to-and-from-Java converters, including both collection and non-collection types, in a single package.
Collection serialization has changed
Collections now use the the serialization proxy pattern uniformly whenever possible. (#6676, #7624, scala-dev#562, sbt/sbt#89)
In some classloading environments, notably sbt's non-forked test execution, code changes may be needed.
Added .unfold
This allows constructing a collection or iterator from an initial element and a repeated Option-returning operation, terminating on None.
This was added collection companion objects and to Iterator (#6851)
Added .lengthIs/.sizeIs and .sizeCompare
These allow fluent size comparisons without traversing the whole collection (#6950, #6758)
Examples: xs.sizeIs < 10, xs.sizeIs == 2
Improved support for extension methods on collections
Offered via IsIterable et al (#6674)
Error-prone Map methods deprecated
Deprecated .filterKeys and .mapValues (#7014)
Instead, use the new methods of the same names on MapView (e.g. .view.filterKeys)
Added .lazyZip
Together with .zip on views, this replaces .zipped (now deprecated). (scala/collection-strawman#223)
Deprecated symbolic methods with multiple arguments
This is because such methods may be disallowed entirely in a future Scala (#6719)
Adding custom collections and operations works very differently
See documentation links below.
To learn more about the new APIs and how to adapt your code, consult:
Scala 2.13's Collections
Intro for newcomers. Skip if the collections from Scala 2.12 and earlier are already familiar to you.
The Architecture of Scala 2.13 Collections
Implementing Custom Collections (Scala 2.13)
Adding Custom Collection Operations (Scala 2.13)
Migrating a Project to 2.13's Collections.
This document describes the main changes for collection users that migrate to Scala 2.13 and shows how to cross-build on Scala 2.11/12/13.
scala-collection-compat
This new module provides shims for cross-building on Scala 2.11/12/13.
It also provides two sets of Scalafix rewrites: one for cross-building, one for moving to 2.13 only.
We welcome assistance in continuing to expand and improve these documents.
Concurrency:
Futures were internally redesigned, with these goals:
provide expected behavior under a broader set of failure conditions
provide a foundation for increased performance
support more robust applications
Details:
Updated and revised our Future and Promise implementation. (#6610, #7663)
Among other changes, handling of InterruptedException and RejectedExecutionException is improved.
Made the global ExecutionContext “batched”. (#7470)
Added synchronous ("parasitic") ExecutionContext. (#7784)
Standard library: additions:
Integrated Java interop (#7987)
The old scala-java8-compat module is now part of the standard library. (#7458)
This provides converters for options, function types and Java streams.
(As mentioned above, collection converters such as JavaConverters were moved to fit into the new scheme.)
new: scala.util.Using
This provides a simple form of automatic resource management. (#6907)
new: .toIntOption, et al
These new extension methods on String are provided by StringOps.
They parse literals and efficiently reject invalid input without throwing exceptions. (#6538)
Examples: "12".toIntOption => Some(12), "12.3".toIntOption => None, "12.3".toDoubleOption => Some(12.3)
new: named Product elements
Case classes and other Products now have productElementNames and productElementName methods. (#6972)
new: .withRight, .withLeft
These methods on Left and Right allow upcasting the other type parameter (#7011, #7080)
Example: Left(3).withRight[String] has type Either[Int, String] without having to write Int
new: Ordering.Double.TotalOrdering, Ordering.Float.TotalOrdering
The old orderings remain available at: Ordering.Double.IeeeOrdering, Ordering.Float.IeeeOrdering
Example: List(2.0, 1.0).sorted is now ambiguous without specifying an ordering
new: pipe and tap
These chaining operations are available via import scala.util.chaining._. (#7007)
Example: 3.pipe(_ * 5) evaluates to 15
Example: 9.tap(println) first prints 9, then returns it
Standard library: changes:
Library fits in compact1 profile
This reduces deployment footprint for Scala applications. (#6164, scala/bug#10559)
Option extends IterableOnce
This improves type inference when calling an overloaded flatMap. (#8038)
Standard library: deprecations and removals:
String-building using + with a non-String type on the left (aka any2stringadd) is now deprecated (#6315, #6755)
PartialFunction.fromFunction replaces PartialFunction.apply (#6703)
Right projections on Either are now deprecated (#6682, #8012)
The following modules are no longer included in the distribution: scala-xml, scala-parser-combinators, scala-swing.
They remain available from Maven Central.
Assorted deprecated methods and classes throughout the standard library have been removed entirely.
Language changes:
2.13 is primarily a library release, not a language/compiler release. Regardless, some language changes are included:
Features:
Literal types
Literals (for strings, integers, and so on) now have associated literal types. (#5310)
See the original proposal, SIP-23, for motivation and details.
The compiler will provide instances of a new typeclass scala.ValueOf[T] for all singleton types T.
The value of a singleton type can be accessed by calling method valueOf[T]. Example: val one: 1 = valueOf[1]
Partial unification on by default
Improves type constructor inference, fixes SI-2712.
We recommend this [great explanation of this feature] (https://gist.github.com/djspiewak/7a81a395c461fd3a09a6941d4cd040f2).
This feature is no longer considered experimental (#5102)
The compiler no longer accepts -Ypartial-unification.
By-name implicits with recursive dictionaries
This extends by-name method arguments to support implicit (not just explicit) parameters.
This enables implicit search to construct recursive values.
The flagship use-case is typeclass derivation.
Details: see the by-name implicits SIP, #6050, #7368
Underscores in numeric literals
Underscores can now be used as a spacer. (#6989)
Example: 1_000_000
Experimental features:
Macro annotations
There is no more "macro paradise" compiler plugin for 2.13.
Instead, macro annotations are handled directly by the compiler.
Macro annotations are enabled with the -Ymacro-annotations flag. #6606
Macro annotations remain experimental.
Deprecations:
Procedure syntax deprecated
Deprecated: def m() { ... }) #6325
Use instead: def m(): Unit = { ... }
View bounds deprecated
Deprecated: A <% B (#6500)
Use instead: (implicit ev: A => B)
Adjustments:
Explicit imports now shadow locally defined identifiers. (#6589)
This is a breaking change.
Better typing for overloaded higher-order methods (#6871, #7631)
This change was a key enabler for the new collections design.
Rework unification of Object and Any in Java/Scala interop (#7966)
Name-based pattern matching has changed to enable immutable Seq matches (#7068)
Automatic eta-expansion of zero-argument methods is no longer deprecated (#7660)
Improve binary stability of extension methods (#7896)
Macros must now have explicit return types (#6942)
Mixin fields with trait setters are no longer JVM final (#7028)
In addition, object fields are now static (#7270)
Support implicitNotFound on parameters (#6340)
Disallow repeated parameters except in method signatures (#7399)
x op () now parses as x.op(()) not x.op() (#7684)
Compiler:
Deterministic, reproducible compilation
The compiler generates identical output for identical input in more cases, for reproducible builds. (scala-dev#405)
Optimizer improvements
Operations on collections and arrays are now optimized more, including improved inlining. (#7133)
And:
Scaladoc supports setting canonical URLs (#7834)
This helps search engines identify the most relevant/recent version of a page when several versions are available.
Compiler suggests possible corrections for unrecognized identifiers (#6711)
Example: List(1).sizzle => value sizzle is not a member of List[Int], did you mean size?
Added -Yimports for custom preamble imports. (#6764)
Example: -Yimports:x,y,z means x, y, and z are root imports of the form: import x._ { import y._ { import z._ { ... } } }
The scala-compiler JAR no longer depends on scala-xml (#6436)
Plus, changes to compiler options:
Replaced -warn-option with -Woption (#7908)
Promoted -deprecation to -Xlint:deprecation (#7714)
Deprecated -Xfuture (#7328)
Instead, use e.g. -Xsource:2.14
Removed -Xmax-classfile-length
It's hard-coded to 240 now (#7497)
Scripting and environment:
The script runner (scala Script.scala) no longer uses the fsc compilation daemon by default. (#6747)
The daemon was not reliable and will likely be removed entirely from a future release.
JEP 293 style long command-line options are now supported (#6499)
The REPL has undergone an internal refactoring to enable future improvements (#7384)
Compiler performance:
We invested heavily in compiler speedups during the 2.13 cycle, but most of that work actually already landed in the 2.12.x series, with more to come in 2.12.9.
In addition, the compiler performance in 2.13 is 5-10% better compared to 2.12, thanks mainly to the new collections. See performance graph.
Also, certain kinds of code now compile much faster because the compiler aggressively prunes polymorphic implicits during search (#6580).
Compatibility:
Like Scala 2.12, the 2.13 series targets Java 8, minimum. Both 2.12 and 2.13 also work on later JDKs such as JDK 11; see our JDK Compatibility Guide.
Although Scala 2.11, 2.12, and 2.13 are mostly source compatible to facilitate cross-building, they are not binary compatible. This allows us to keep improving the Scala compiler and standard library.
All 2.13.x releases will be fully binary compatible with 2.13.0, in according with the policy we have followed since 2.10.
The list of open-source libraries released for Scala 2.13 is growing quickly!
Projects built with sbt must use at least sbt 1.2.8 (or 0.13.18) to use Scala 2.13. To move to 2.13, bump the scalaVersion setting in your existing project.
Scala also works with Maven, Gradle, and other build tools.

New in Scala 2.12.8 (Dec 6, 2018)

New in Scala 2.12.7 (Sep 27, 2018)

New in Scala 2.13.0-M5 (Aug 31, 2018)

Collections changes:
The major collections changes already landed in M4. See the M4 release notes for a summary.
To learn more about those changes and how to adapt your code, take a look at the FAQ wiki page. This document is intended for library maintainers and assumes familiarity with the 2.12 Scala collections. Additional documentation will become available soon.
Here's the biggest additional collections changes since M4:
The new CHAMP-based HashMap and HashSet implementations are now the default (#7074)
A LazyList's empty-or-not status is now lazy too (#7000)
Variables bound in pattern matches by the x @ _* syntax are now typed scala.Seq (immutable); name-based pattern matching has changed to enable this (#7068)
Arrays passed as varargs are now defensively copied (#6970)
Offer stronger guarantees under the Java Memory Model for List and Vector (using releaseFence) (#6425)
Iterator and collection companion objects now have an .unfold method (#6851)
Collections now have .lengthIs, .sizeCompare and .sizeIs methods (#6950, #6758)
Improved support for extension methods on collections via IsIterable et al (#6674)
Now deprecated: .zipped (#7025), .filterKeys and .mapValues (#7014), symbolic methods with multiple arguments (#6719)
Added immutable maps that maintain insertion order (VectorMap/SeqMap) (#6854), but note that VectorMaps remove method was found to be incorrect; the next release will have a fix.
Language and compiler changes:
Compiler output is now deterministic, for reproducible builds (scala-dev#405)
Support by-name implicits with recursive dictionaries (#6050)
Better typing for overloaded higher-order methods (#6871)
Improved compiled times by more aggressively pruning polymorphic implicits during search (#6580)
Explicit imports now shadow locally defined identifiers (#6589)
Mixin fields with trait setters are no longer JVM final (#7028)
Library additions and changes:
Updated & revised Future and Promise implementation (#6610)
Added scala.util.Using, for automatic resource management (#6907)
Added Option-returning methods (e.g. toIntOption) for parsing literals (#6538)
Case classes and other Products now have productElementNames and productElementName methods (#6972
Left and Right now have .withRight and .withLeft methods for upcasting the other type parameter (#7011)
Added tap and pipe methods, for chaining operations, available via import scala.util.chaining._ (#7007)
Added total orderings for Float and Double (#6410)
String-building using + on non-String types is now deprecated (#6315, #6755)
Projections on Either are now deprecated (#6682)
PartialFunction.fromFunction replaces PartialFunction.apply (#6703)
Support implicitNotFound on parameters (#6340)
Environment and compiler option changes:
Added -Yimports for implicit preamble imports (#6764)
Support JEP 293 style long command-line options (#6499)
The script runner no longer uses the fsc compilation daemon by default (#6747)
Removed -Yrepl-sync (#6626)

New in Scala 2.12.6 (Apr 28, 2018)

New in Scala 2.12.5 (Mar 20, 2018)

New in Scala 2.13.0-M1 Development (Jul 31, 2017)

New in Scala 2.12.2 (Jul 25, 2017)

New in Scala 2.12.0-M2 Development (Aug 22, 2015)

New in Scala 2.11.7 (Jun 26, 2015)

New in Scala 2.11.6 (Mar 6, 2015)

New in Scala 2.11.5 (Jan 15, 2015)

Scala 2.11.5 is a bugfix release that is binary compatible with previous releases in the Scala 2.11 series. We would like to highlight the following changes:
heathermiller’s SI-6502 Reenables loading jars into the running REPL
mpociecha’s The alternative, flat representation of classpath elements
gbasler’s Avoid the ‘CNF budget exceeded’ exception via smarter translation into CNF
adriaanm’s SAMmy: eta-expansion, overloading, existentials
A great number of documentation improvements
FIXED ISSUES:
Bug SI-8927: Warning on every Scala compile: "POM for 'biz.aQute:bndlib:pom:1.43.0:compile' is invalid."
Bug SI-8966: In Scalac.scala jvm-1.8 is not an allowed target for the ant tool
Bug SI-8783: MultiMap documentation for addBinding is incorrect, or there is a bug
Improvement SI-9043: ArrayBuffer.insert and insertAll are very slow
Bug SI-8924: List iterator holds reference to list's head
Bug SI-6519: PagedSeq is not lazy enough
Bug SI-8932: many dropRight/takeRight implementations are wrong
Bug SI-8754: linear seqs aren't
Bug SI-8538: BufferedSource not that usable without deprecated Position
Bug SI-8951: SeqView and StreamView stack-overflow on negative index after flatMap
Bug SI-8910: scala.collection.mutable.BitSet uses exponentially growing memory under certain conditions.
Bug SI-8695: SeqLike has either a buggy or highly unintuitive implementation of combinations
Bug SI-7019: value class compiler crash with private[this]
Bug SI-8931: Class Signature attribute inconsistent with interfaces
Bug SI-7965: Support for @PolymorphicSignature, required for using MethodHandles from Scala
Improvement SI-7444: Improvement to ExecutionContext ScalaDoc
Bug SI-8995: Scala documentation link emitted by compiler returns a 404 (scala.xml)
Bug SI-8948: Any/AnyRef/Null scaladoc MIA
Bug SI-7988: scala.collection.JavaConverters spelling mistake
Improvement SI-8916: Clean up unused imports, values and variables
Bug SI-8934: quasiquote unapply macro gives spurious "wrong number of subpatterns" under presentation compiler
Bug SI-8947: New ambiguous implicits error in Scala 2.11.4 (works in 2.11.2) with macros
Bug SI-9044: Interface List Reversed in Classfile
Bug SI-6541: compiler infers non-wildcard existential type for case-module-unapply
Bug SI-8933: Unexpected java.lang.IllegalAccessError thrown when accessing symbols in traits with self type
Bug SI-8502: graceless failure of stub symbols in erasure phase
Bug SI-6613: fsc crashes every other time on inner Java enums
Bug SI-7596: type error on separate compilation (pickler foiled by path dependent parent type in the presence of overloading)
Bug SI-9018: Compiler hangs when match returns different types
Bug SI-7750: Spurious scala.language.existentials warning triggered by isInstanceOf in LazyCombiner
Bug SI-3439: consider implicits constructor params in super-ctor call
Bug SI-8967: Scala scripts can throw JVM error if extra files placed in SCALA_HOME/lib
Bug SI-8893: exponential compiler performance with nested pattern matches under tailrec transform
Bug SI-5938: Get "Duplicate method name&signature" on recompile only
Bug SI-5217: I expect private constructor's parameter type is in private scope, but scalac does not allow that.
Bug SI-9015: Nuance errors for zero-led literals
Bug SI-8960: Anonymous Functions don't have a SerialVersionUID anymore since 2.11.1
Bug SI-7683: Can't stop after phases between parser and typer
Bug SI-8965: Warning indicates Any and Any are unrelated
Bug SI-8711: Scala version's unparse is unsightly
Bug SI-9030: BoxesRunTime.equalsNumChar should be public
Bug SI-8970: hashCode of BigDecimal and Double do not match in 2.11
Bug SI-8977: scalap jar file contains duplicate entry
Bug SI-8999: OutOfMemoryError in pattern analysis
Bug SI-8962: Covariant tparam appearing multiple times receives wrong inferred type in patmat RHS
Bug SI-7459: Pattern Matcher substitution doesn't handle references in singleton types
Bug SI-8597: missing unchecked warning for `case _: Some[AbstractType]`
Bug SI-9003: name-based pattern matching could lead to undefined behaviour in runtime
Bug SI-9011: ClassCastException: Trees$DocDef cannot be cast to Trees$ClassDef
Bug SI-8943: Spurious errors in case classes with private vals
Bug SI-8941: namer to typer handoff of synthetic implicit class factory method breaks under presentation compiler if interrupted
Bug SI-8875: showCode does not print class constructor modifiers
Bug SI-8946: scala.reflect.runtime.ThreadLocalStorage$MyThreadLocalStorage is forever retaining references to threads
Bug SI-6502: :cp does not work
Bug SI-8898: REPL `:javap -fun` broken under `-Ydelambdafy:method`
Improvement SI-8922: REPL verbose load
Bug SI-4950: val 1 = 2 and other value declarations that don't declare any values confuse the REPL
Improvement SI-9006: Scaladoc companion and package links hard for newcomers to find
Bug SI-5730: Constructor listing in ScalaDoc ignore "Visibility" setting
Bug SI-6626: @throws tags do not create clickable links
Bug SI-5583: REPL crasher in specialize, "scala.reflect.internal.Types$TypeError: method foreach$mVc$sp: (f: Int => Unit)Unit does not take type parameters"
Bug SI-8871: call to specialized method fails second time under fsc or REPL
Bug SI-6856: trivial wrong(old) comment
Bug SI-8534: compiler crash rather than message "XXZ is not an enclosing class" in erroneous code
Bug SI-7602: method defined twice + lub = AssertionError
Bug SI-8449: Typechecker doesn't allow a Java raw type over a Scala type
Bug SI-5091: Unexpected "recursive value needs type" error
Bug SI-9008: Higher-kinded existentials are broken
Bug SI-5454: Spurious illegal inheritance error & implicit resolution failure with parent class implicit constructor argument
Bug SI-9027: Semicolon is not inferred after a XML node sequence literal
Bug SI-8253: xml parsing blindly interprets spliced method call in xmlns attribute as xml.Text("uri")
Improvement SI-8310: sams could play nicer with overloading
Bug SI-8950: SeqView and StreamView allow indexing out of a slice (and updating in!)
Bug SI-6051: Lazy modifier on a val causes its name to collide with a method's named arg

New in Scala 2.11.4 (Nov 11, 2014)

New in Scala 2.11.2 (Jul 24, 2014)

New in Scala 2.10.4 RC3 (Feb 27, 2014)

Improvements:
Eta-expansion too conservative wrt dependent method type
Bug fixes:
backport fix for exponential-time variance validation to 2.10.x
Non-deterministic type errors and non-termination of scalac
ClassFormatError in pattern of code use by Slick
presentation compiler reports false positive: illegal cyclic reference involving package
regression in trait superaccessors with overloading
Scope completion marks vars and vals accessible through the getters as non-accessible
include required license texts
spurious errors / crashes when pattern matching meets super
uncaught exception during compilation: "Could not find proxy for ..."
Presentation compiler fails to resolve implicit defined in package object
askTypeAt returns overloaded types
When falling back to adapt without an expected type, use of resetAttrs leads to unhygenic rebinding
Completions not found for members imported from an object
:javap generates "Could not find class bytes ..." error
MSI installer for Windows sets path variable incorrectly
hang in inliner with recursive higher-order method, separate compilation
compiler freezes when typing an eta expansion involving a type constructor
swing.Publisher calls PartialFunction listeners for undefined values
Call of updateDynamic results in NoPosition error
Call of applyDynamicNamed results in NoPosition error
Wrong position for applyDynamic call
Wrong Tree returned by `askTypeAt` (wrong hyperlink)
Be defensive when calling toString() on object in MatchError.getMessage
Compiler fails strangely on some higher-order kinds
don't issue deprecation warnings for synthetic TypeTrees
Future.fallbackTo does not preserve first Future's Failure per documentation
lambdalift crashes when Block in constructor-argument position requires outer() access
Optimizer leaves references to classes that have been eliminated by inlining
Wrong position for selectDynamic call
Class file is broken (Vaadin)
Backport tools.jar robustness for REPL, fail loud
ScriptEngineManager providers.next(): javax.script.ScriptEngineFactory: Provider scala.tools.nsc.interpreter.IMain$Factory not found

New in Scala 2.10.4 RC2 (Feb 5, 2014)

New in Scala 2.11.0-M8 (Jan 30, 2014)

New in Scala 2.11.0-M7 (Dec 27, 2013)

New in Scala 2.10.3 (Oct 2, 2013)

Fixed:
MANIFEST.MF file for Scala sources
Don't execute internal callbacks on the user Executor
Enable test for Java 8 source parser under Java 8
Consider DEFAULTMETHOD when refchecking concreteness
Cast our way out of extended existential angst
Test case for Scaladoc on early initializers
avoid rejecting Scaladoc comments in early initializers
Rework MapLike#retains to account for desugaring change
Updates the instrumented version of ScalaRuntime.
Avoid init cycle between Predef, `package`, ScalaRuntime
REPL extended quest for tools
Bad tools fails loudly
Use a WeakHashSet for type uniqueness
Replace scala.reflect.internal.WeakHashSet
Derive type skolems at the ground level
Parser handles block-ending import
No ScriptEngine in 2.10 build
Harden against the shifting sands of System.getProperties
Account for class name compactification in reflection
More tests for cycles triggered by implicit search
A test case, five years adrift.
Exclude patmat synthetics from bounds checking
Remove diagnostic code for annotation error
Fix thread safety of FlagTranslation
Don't disambiguate type parameters of overloaded alts
Annot arg may refer to annotated class's member
Add @uncheckedBounds to the library
@uncheckedBounds, an opt-out from type bounds checking
Determinism for pattern matcher warnings
reflective packages now more consistent with scalac
tb.parse returns unpositioned trees
scala.bat honors -J and -D options.
Drop dummy param for synthetic access constructor
Fix a NPE in typing class constructors
Handle spaces in %COMSPEC% path in scala.bat.
Fix end position in PostfixSelect tree
clarifies the "macro overrides method" rule
Link flatMapped promises to avoid memory leaks
General test for spec version
Fix positions for reshaped tag materializers
typedAssign no longer expands lhs
Superaccessor lookup after specialization
Speculative fix for annotation binding error
Specialize methods in private scopes
Allow nesting of anonymous classes in value classes
Fixed phase ordering in specialization
ParTrieMap.foreach no longer crashes
Test case for pattern matcher + type alias bug
Fix bug at the intersection of DelayedInit and named args
Fix capture of free local vars in toolbox compiler
Fix runtime reflection involving ScalaLongSignature
Fix lookup of private[this] member in presence of self type.
ClassTag for value class aliases
Centralize and refine detection of `getClass` calls
Always use ForkJoin in Scala actors on ... ... Java 6 and above (except
Bad for expr crashes postfix
remove unneeded extra-attachement in maven deploy
Fix scala.util.Properties.isMac

New in Scala 2.11.0-M5 (Sep 30, 2013)

New in Scala 2.10.3-RC2 (Sep 19, 2013)

NEW FEATURES AND IMPROVEMENTS:
Value Classes:
A class may now extend AnyVal to make it behave like a struct type (restrictions apply).
Implicit Classes:
The implicit modifier now also applies to class definitions to reduce the boilerplate of implicit wrappers.
String Interpolation:
val what = "awesome"; println(s"string interpolation is ${what.toUpperCase}!")
Futures and Promises:
Asynchronously get some JSON: for (req < - WS.url(restApiUrl).get()) yield (req.json \ "users").as[List[User]] (uses play!)
Dynamic and applyDynamic:
x.foo becomes x.applyDynamic("foo") if x’s type does not define a foo, but is a subtype of Dynamic
Dependent method types:
def identity(x: AnyRef): x.type = x // the return type says we return exactly what we got
New ByteCode emitter based on ASM:
Can target JDK 1.5, 1.6 and 1.7
Emits 1.6 bytecode by default
Old 1.5 backend is deprecated
A new Pattern Matcher:
rewritten from scratch to generate more robust code (no more exponential blow-up!)
code generation and analyses are now independent (the latter can be turned off with -Xno-patmat-analysis)
Scaladoc Improvements:
Implicits (-implicits flag)
Diagrams (-diagrams flag, requires graphviz)
Groups (-groups)
Modularized Language features:
Get on top of the advanced Scala features used in your codebase by explicitly importing them.
Parallel Collections are now configurable with custom thread pools
Akka Actors now part of the distribution:
scala.actors have been deprecated and the akka implementation is now included in the distribution.
Performance Improvements:
Faster inliner
Range#sum is now O(1)
Update of ForkJoin library
Fixes in immutable TreeSet/TreeMap
Improvements to PartialFunctions
Addition of ??? and NotImplementedError
Addition of IsTraversableOnce + IsTraversableLike type classes for extension methods
Deprecations and cleanup:
Floating point and octal literal syntax deprecation
Removed scala.dbc
EXPERIMENTAL FEATURES:
Scala Reflection
Macros
FIXED:
Enable test for Java 8 source parser under Java 8
Consider DEFAULTMETHOD when refchecking concreteness
Cast our way out of extended existential angst
avoid rejecting Scaladoc comments in early initializers
Rework MapLike#retains to account for desugaring change
Updates the instrumented version of ScalaRuntime.
Avoid init cycle between Predef, `package`, ScalaRuntime
REPL extended quest for tools
Bad tools fails loudly
Use a WeakHashSet for type uniqueness
Replace scala.reflect.internal.WeakHashSet
Derive type skolems at the ground level
Parser handles block-ending import
No ScriptEngine in 2.10 build
Harden against the shifting sands of System.getProperties
Account for class name compactification in reflection
More tests for cycles triggered by implicit search
A test case, five years adrift.
Exclude patmat synthetics from bounds checking
Remove diagnostic code for annotation error
Fix thread safety of FlagTranslation
Don't disambiguate type parameters of overloaded alts
Annot arg may refer to annotated class's member
Add @uncheckedBounds to the library
@uncheckedBounds, an opt-out from type bounds checking
Determinism for pattern matcher warnings
reflective packages now more consistent with scalac
tb.parse returns unpositioned trees
scala.bat honors -J and -D options.
Drop dummy param for synthetic access constructor
Fix a NPE in typing class constructors
Handle spaces in %COMSPEC% path in scala.bat.
Fix end position in PostfixSelect tree
clarifies the "macro overrides method" rule
Link flatMapped promises to avoid memory leaks
General test for spec version
Fix positions for reshaped tag materializers
typedAssign no longer expands lhs
Superaccessor lookup after specialization
Speculative fix for annotation binding error
Specialize methods in private scopes
Allow nesting of anonymous classes in value classes
Fixed phase ordering in specialization
ParTrieMap.foreach no longer crashes
Test case for pattern matcher + type alias bug
Fix bug at the intersection of DelayedInit and named args
Fix capture of free local vars in toolbox compiler
Fix runtime reflection involving ScalaLongSignature
Fix lookup of private[this] member in presence of self type.
ClassTag for value class aliases
Centralize and refine detection of `getClass` calls
Always use ForkJoin in Scala actors on ... ... Java 6 and above (except
Bad for expr crashes postfix
remove unneeded extra-attachement in maven deploy
Fix scala.util.Properties.isMac

New in Scala 2.10.2 RC1 (May 23, 2013)

Bug fixes:
unit value equality is broken when deserialized
checkinit build failure after SI-6387
java.lang.RuntimeException: no acc def buf for package interpolation
Memory leak caused by scala.reflect.internal.util.Statistics
scala now thinks every exception is polymorphic
java.lang.NoSuchFieldError: $outer when mixing Scala and Java
cannot reify existentially typed code
pattern matcher exhaustiveness warnings include impossible types
crashers in annotation argument handling in scaladoc
Insufficient task support detection mechanism chooses fails to choose ForkJoin even when available/supported
divergent implicit machinery prevents implicit macros from recursing
Implicit macros are broken
Fork Join's idle hands
check consistency of version numbers in build
f string interpolator no longer accepts literal %
by-name argument creates spurious type mismatch
spurious cyclic ref error with nested java class
Partest --show-log not showing compilation errors
Implicit value instances of inner class defined in superclass of package object don't resolve on import
ListMap produces incorrect exception message
NPE in parser in forScaladoc mode
spurious "scrutinee is incompatible with pattern type; found T.this.A, required T#A"
Compiler crashes when evaluating XML element followed by "()"
Interactive doc: allow to pass overridden symbols
Transpose on empty Array throws NoSuchElementException
Pattern matcher outer check generation fooled by type aliases
Bad range position for super type
Two crashers for reify/patmat
Type inference does not work on methods using dependent types and parameters with default value
regression in type inference
named/defaults crasher with sequence argument of the wrong type
language features fail to be found during mixin
:type doesn't understand Unit
"no-symbol does not have an owner" with Scala 2.10 (named args side effects on trees)
Passing a Function0 invocation to a call by name argument *should* create a new Function0 if the original Function0 is not stable
incorrect error message for missing annotation
Spurious test failure in t6223 because test assumes specific order of reflection values
scala.reflect.internal.Types$TypeError: ambiguous reference to overloaded definition
SQLiteDatabase cannot be closed in Android 4.0 or below devices, in apps built by Scala 2.10.x w/ Android 4.1 due to Scala 2.10.x bytecode problem.
Java parser incorrect tree
Import-renamed method can't be used as partially applied function
In-place silent type checking, adaptToMemberWithArgs, filter/withFilter => "erroneous or inaccessible type"
duplicate keys in SWITCH
path-dependent types and recursion => crash
memory leak in specialize
schtroumpfs crash type inference
(runtime.universe: api.Universe).typeTag[A] throws Error
Can not reify existential type alias when underlying is higher kinded type
Compiler throws IllegalArgumentException handling specialized method implementation
Java source parser does not follow Java rules for shadowing.
Compiler crashes when class is set to private of non-enclosing scope
resetLocalAttrs followed by typeCheck causes error
double definition error due to specialized constructor argument with default value
regression (since 2.9): pattern matcher chokes on invalid pattern with type parameter
scala.bat cannot handle space in paths
No compiler warning for valueClassInstance == value
pattern matcher - exhaustiveness check reports wrong warnings
Scaladoc parser crashes with a StackOverflow
images in ScalaDoc are doubled
Higher-kinded type alias may cause incorrect unreachable code warning
Logic of ThreadPoolConfig.useForkJoin causes test concurrent-stream.scala to randomly hang
"unreachable code" warning on reachable code
'silent=false' is not working at c.inferImplicitValue
DivergentImplicit exception is thrown by c.inferImplicitValue even if silent is set to true
@annotation(typeOf[String]) crashes in pickler with AssertionError
ExecutionContext.prepare is not invoked by Future.apply
String interpolated parts get assigned with incorrect positions
Filtering classes no more works properly
The Collection API documentation is missing an example for transpose
FieldMirror.set should allow setting vals
Classfiles in the standard library are missing Sourcefile attribute
scaladoc for just src/reflect crashes
Dead code warning in case statement when throwing an exception returned by a method call
REPL corruption after ambiguous implicit error
Reflection: MissingRequirementError for top-level classes with escaped names
Constructor parameters become inaccessible in body if passed to base constructor argument in private [namespace] scope
Compiler crash during parsing because of `while` condition lacks parentheses
Misleading error message when trying to eta-expand method with more than 22 parameters
java.lang.AssertionError scaladoc'ing class with a Java annotation
supplementErrorMessage should swallow TypeError
Scaladoc throws next on empty iterator
non-sensible equality method doesn't account for overloading
Scaladoc: if the index is missing members under a letter, clicking the letter will yield 404
Improvements:
Add guides for new Scala 2.10.0 features to docs.scala-lang.org
Add section to published pom.xml for auto-scaladoc linking in sbt
Scaladoc for interactive: don't require doc settings
Test interactive documentation for more cases
f string interpolator does not support %n (platform line separator) specifier
Update bundled Fork/Join (JSR166)
allow pattern with identifier that would be stable if it wasn't for its volatile type

New in Scala 2.10.1 RC1 (Feb 15, 2013)

Commits and the issues they fixed since v2.10.0:
Revert "SI-6548 reflection now correctly enters jinners"
Revert "SI-4664 Make scala.util.Random Serializable"
Revert "Fixes SI-6521, overrides Range#head to be faster"
SI-5675 Discard duplicate feature warnings at a position
SI-6591 Reify and path-dependent types
SI-7096 SubstSymMap copies trees before modifying their symbols
SI-6961 no structural sharing in list serialization
SI-6187 Make partial functions re-typable
[backport] SI-6478 Fixing JavaTokenParser ident
SI-7100 Fixed infinite recursion in duplicators
SI-6146 More accurate prefixes for sealed subtypes.
SI-5082 Cycle avoidance between case companions
SI-6113 typeOf now works for type lambdas
SI-5824 Fix crashes in reify with _*
SI-7026: parseTree should never return a typed one
Revert "SI-5017 Poor performance of :+ operator on Arrays"
SI-7070 Turn restriction on companions in pkg objs into warning
SI-6773 Makes the SI-6150 changes binary compatible with 2.10
SI-7060 More conservative dead code elim marking
SI-6888 Loosen criteria for $outer search.
SI-6989 privateWithin is now populated in reflect
[nomerge] SI-6667 Demote a new ambiguity error to a lint warning.
SI-5833 Fixes tail-of-Nil problem in RefinedType#normalizeImpl
Revert "SI-6422: add missing Fractional and Integral alias in scala package"
Class symbols can't be contravariant.
SI-1803, plus documentation and cleanups in Namers, mainly in typeSig
SI-6017 Scaladoc: Show all letters without dangling links
SI-6017 Generate Scaladoc's index links in Scala side
SI-5313 Minor code cleanup for store clobbering
SI-5313 Test clobbers on the back edge of a loop
SI-6666 Catch VerifyErrors in the making in early defs.
Add a test case from the comments of SI-6666.
SI-6666 Account for nesting in setting INCONSTRUCTOR
SI-7033 Be symful when creating factory methods.
SI-7022 Additional test case for value class w. bounds
[backport] SI-6482, lost bounds in extension methods.
SI-7039 unapplySeq result type independent of subpattern count
SI-7008 @throws annotations are now populated in reflect
Fix SI-6578. Deprecated `askType` because of possible race conditions in type checker.
SI-7029 - Make test more robust
SI-4714 Initialize history while initializing the REPL's reader
SI-2818 Make List.foldRight always do a reverse/foldLeft flip
SI-3353 don't extract into named-arg local val
SI-7029 - Makes sure that uncaught exceptions are propagated to the UEH for the global ExecutionContext
SI-6686 drop valdef unused in flatMapCond's block
don't store subpats bound to underscore
SI-7046 reflection now auto-initializes knownDirectSubclasses
[backport] Removed restriction on final vars, SI-2418.
SI-6812 scaladoc can opt out of expanding macros
SI-6539 moves @compileTimeOnly away from scala-reflect
SI-6669 Add . to the default scalap classpath
SI-6728 Fixes crash in parser on incomplete for expression
SI-6516, macros comparing types with == instead of =:=.
SI-7009: `@throws` annotation synthesized incorrectly
SI-5313 Eliminate more stores by replacing clobbers with null stores
SI-6726 Further optimization of pattern analysis
SI-6726 Hash consing for Pattern matching Sym-s
SI-6726 Add benchmark used for testing pattern matcher.
SI-6595, lost modifiers in early defs.
SI-6584, Stream#distinct uses too much memory.
SI-6426, importable _.
SI-6072, crasher with overloaded eq.
SI-5604, selections on package objects.
SI-5859, inapplicable varargs.
SI-5353, imperfect error message.
SI-5130, precision disappearing from refinement.
SI-4729, overriding java varargs in scala.
SI-2418, remove restriction on final vars.
Test case for SI-7009.
SI-6551 Expand test case into uncomfortable areas.
SI-6651 Substitute `this` in extension method sigs
SI-6963 Add version to -Xmigration
[backport] Disabled SI-6987.
[backport] Fix for SI-6154, VerifyError originating in uncurry.
SI-6572 Test case, originally fixed in a3680be.
[backport] SI-6301 / SI-6572 specialization regressions
SI-5313 Do not eliminate stores that potentially wipe referenes
[backport] SI-5378, unsoundness with type bounds in refinements.
SI-7035 Centralize case field accessor sorting.
SI-6968 Simple Tuple patterns aren't irrefutable
SI-4602 Disable unreliable test of fsc path absolutization
A test case to guide the eventual fix for SI-6601.
SI-7018 Fix memory leak in Attachments.
SI-4733 - fsc no longer creates a single temp directory for all users.
[backport] SI-3577 BoundedWildcardType handling
[backport] SI-2968 Fix brace healing for `^case (class|object) {
[backport] Fix for SI-6206, inconsistency with apply.
SI-6891 Fix value class + tailrec crasher.
Revert "SI-6601 Publicise derived value contstructor after pickler"
SI-4602 Make fsc absolutize source file names
SI-6863 Fix verify error in captured var inited from expr with try/catch
SI-6853 changed private method remove to be tail recursive. Operations += and -= on mutable.ListMap rely on the private method remove to perform. This methods was implemented using recursion, but it was not tail recursive. When the ListMap got too big the += caused a StackOverflowError.
SI-6969, mishandling of SoftReferences in method cache.
SI-6434 Pretty print function types with by name arg as (=> A) => B
SI-7011 Fix finding constructor type in captured var definitions
[backport] SI-6567 Warning for Option(implicitView(foo))
[backport] Fix unsafe array opt. / opt. primitive Array(...)
[backport] Fix SI-6637 (misoptimization in erasure)
SI-6987 Tests fsc verbose output
SI-6987 Fixes fsc compile server verbose output
SI-6932 Remove Batchable trait plus minor clean-ups
Fix SI-6932 by enabling linearization of callback execution for the internal execution context of Future
SI-6231 Report unsupported free var capture by a trait.
SI-6666 Restrict hidden `this` access in self/super calls.
SI-6994 Avoid spurious promiscuous catch warning
Addressing warnings.
SI-6439 Avoid spurious REPL warnings about companionship
SI-6902 Check unreachability under @unchecked
SI-6942 more efficient unreachability analysis
SI-6601 Publicise derived value contstructor after pickler
SI-4976 Scaladoc: Add a source link to package objects
SI-6976 Fix value class separate compilation crasher.
SI-6443 Expand test coverage with varargs, by-name.
SI-6443 Widen dependent param types in uncurry
SI-6017 Scaladoc's Index should be case-sensitive
Closes SI-6952: add correct error positions for Dynamic feature check.
SI-6956 determine switchability by type, not tree
SI-5568 Comment improvements for getClass on primitive intersection.
SI-5568 Fixes verify error from getClass on refinement of value type
SI-6675 Test new warning under -Xoldpatmat.
SI-6675 -Xlint arity enforcement for extractors
SI-6905 - Switch to sneakyThrows instead of Unsafe.throwException as per new jsr166y to avoid issues with Android
SI-6963 Deprecates -Xmigration switch
SI-5954 Implementation restriction preventing companions in package objs
SI-6479 Don't lift try exprs in label arguments.
SI-6082 Conditionally expand @ann(x) to @ann(value = x)
SI-6126 Test case for varargs of tagged primitives.
SI-5440 Test case for exhaustiveness check
SI-5340 Change println to log
SI-6955 switch emission no longer foiled by type alias
SI-6925 use concrete type in applyOrElse's match's selector
SI-5189 detect unsoundness when inferring type of match
SI-6946, SI-6924 79a722feb9 SI-6946, SI-6924 Greatly improves IsTraversableLike docs
SI-6555 Scaladoc's class filter shouldn't drop the last character
Backport of SI-6846.
Fixes SI-6521, overrides Range#head to be faster
SI-6641 Deprecate SwingWorker
SI-6930 adds documentation to reduceLeft in TraversableOnce
SI-6912 Avoid a typer cycle in overload resolution.
SI-6928, VerifyError with self reference to super.
SI-6923 Context now buffers warnings as well as errors
SI-6803: do not use java.net.URI, even more so incorrectly.
Fix Iterator#copyToArray (fixes SI-6827).
SI-6911, regression in generated case class equality.
SI-6897, lubs and varargs star.
SI-6896, spurious warning with overloaded main.
SI-6415, overly eager evaluation in Stream.
SI-6194, repl crash.
SI-6829, SI-6788, NPEs during erroneous compilation.
SI-5017 Poor performance of :+ operator on Arrays
SI-6288 Remedy ill-positioned extractor binding.
SI-6288 Fix positioning of label jumps
SI-6288 Position argument of unapply
Fixes SI-6758: force LazyAnnnotationInfo for DefDef and TypeDef
SI-5841 reification of renamed imports
SI-6795 Simplify errors related to "abstract override" on type members
SI-6795 Adds negative check for "abstract override" on types in traits
SI-4922 Show default in Scaladoc for generic methods.
SI-6555 Better parameter name retention
SI-6614 Test case for fixed ArrayStack misconduct.
SI-6690 Release reference to last dequeued element.
SI-5789 Use the ReplTest framework in the test
SI-5789 Checks in the right version of the test
SI-5789 Removes assertion about implclass flag in Mixin.scala
SI-6548 reflection now correctly enters jinners
SI-6766 Makes the -Pcontinuations:enable flag a project specific preference
SI-6696 removes "helper" tree factory methods
SI-6766 Create a continuations project in eclipse
SI-6746 Fixes MANIFEST.MF package entry (s.r.makro -> s.r.macros)
SI-6338 fixes the unchecked warning in quick.comp
SI-5894 Don't emit static forwarders for macros.
SI-1672 Catches are in tail position without finally.
SI-5361 Refactor in accordance with review comments.
SI-3995 Exclude companions with an existential prefix.
SI-5390 Detect forward reference of case class apply
SI-5361 Avoid cyclic type with malformed refinement
SI-5877 Tweak the check for package object owner.
tests for idempotency issues in the typechecker
SI-5877 Support implicit classes in package objects
Adds debug logging for synthetic registration.
SI-6535 Step back from the precipice of a cycle
SI-4664 [Make scala.util.Random Serializable] Add test case
SI-6549 Improve escaping in REPL codegen.
SI-6547: elide box unbox pair only when primitives match
SI-6558 Expand test case for annotation typos
Fixes SI-6558: typecheck lazy annotation info using non-silent context.
SI-6631 Handle invalid escapes in string interpolators
SI-4664 Make scala.util.Random Serializable
Test cases for SI-5726, SI-5733, SI-6320, SI-6551, SI-6722.
Fix for SI-6731, dropped trees in selectDynamic.
SI-5753 macros cannot be loaded when inherited from a class or a trait
SI-5678 Bad return type for [Use Case] docs in Range
SI-6667 Abort after any ambiguous in-scope implicit
SI-6718 fixes a volatile test
Fix for SI-6712, bug in object lifting.
Fix for SI-6687, wrong isVar logic.
Fix for SI-6706, Symbol breakage under GC.
SI-6023 reify abstract vals
SI-6695 Test case for fixed Array match bug
Fix for SI-6357, cycle with value classes.
SI-6673 fixes macro problems with eta expansions
SI-6677 Insert required cast in `new qual.foo.T
SI-6663: don't ignore type parameter on selectDynamic invocation
SI-6551: don't insert apply call in polymorphic expression.
SI-6634 Fixes data corruption issue in ListBuffer#remove
Fixes SI-6150 - backport to 2.10.x branch.
SI-5330, SI-6014 deal with existential self-type
Fix for SI-6662, macro failing too early.
better error when typetagging local classes
SI-6632 SI-6633 Fixes issues and data corruption in ListBuffer
SI-6539 Annotation for methods unfit for post-typer ASTs
SI-6616 Check that unsafe operations are only called on the presentation compiler thread.
Fix for SI-6597, implicit case class crasher.
Fixes SI-6559 - StringContext not using passed in escape function.
SI-6488: Stop I/O threads prior to Process destruction
Added one more test for SI-6358
Closes SI-6358. Move accessor generation for lazy vals to typers.
SI-6422: add missing Fractional and Integral alias in scala package

New in Scala 2.10.0 (Jan 4, 2013)

New in Scala 2.9.3 RC 1 (Dec 15, 2012)

New in Scala 2.10.0-RC3 (Dec 3, 2012)

New in Scala 2.10.0-RC2 (Nov 9, 2012)

New in Scala 2.10.0-M7 (Aug 28, 2012)

Performance Improvements
Macros:
c.reify removed, use c.universe.reify instead
scala.reflect.makro renamed to scala.reflect.macros
Usages of macros no longer require scala-reflect.jar on library classpath
Macros now only allow c.AbsTypeTag context bounds (details). Use c.AbsTypeTag instead of c.TypeTag, implicitly[c.AbsTypeTag[T]].tpe instead of c.typeOf[T] (in RC1 there will be a shortcut, c.absTypeOf[T])
Breakage!! Macro impls for macro defs with implicit parameters cannot have type tag context bounds: https://issues.scala-lang.org/browse/SI-6281. Fixed in RC1, see the linked issue for a workaround.
Reflection:
Introduced MethodSymbol.{params, typeParams, returnType}
asXXXSymbol renamed to asXXX, asType renamed to Type, asTypeConstructor renamed to toTypeConstructor
Introduced TermSymbol.{getter, setter, accessed} to navigate between accessor symbols and underlying field symbols
Flags on symbols are gone and replaced with a lot of new isXXX tests
Some isXXX tests on symbols moved from Symbol to descendants
Breakage!! isXXX tests don’t work unless a symbol is initialized: https://issues.scala-lang.org/browse/SI-6277. Will be fixed in RC1, see the linked issue for a workaround.
Some methods on types are gone and should be replaced by pattern matching (e.g. Type.typeParams is removed and is supposed to be acquired by matching against PolyType)
TermSymbol.resolveOverloaded is removed and is planned to be resurrected in 2.10.1
base.StandardNames and api.StandardNames have undergone a drastic cleanup
Implementation of mirrors is now complete: ModuleMirror.instance works for nested modules, MethodMirror.apply support magic symbols, mirrors correctly work with value classes, etc
See this thread for some info about migration: http://groups.google.com/group/scala-internals/browse_thread/thread/4758995dfa2da9db
ClassTag.Nothing now throws an exception to emphasize the fact that there are no values of type Nothing. On a second thought, this is deemed to be a mistake and is reverted in RC1.

New in Scala 2.10.0-M6 (Aug 1, 2012)

New in this milestone:
Akka actors jar now included in distribution.
Backend emits Java 1.6 class files by default. Generation of Java 1.5 class files has been deprecated. Non-default class file formats can be emitted via -target:jvm-1.5 and -target:jvm-1.7.
Fixed:
SI-6112 exposes symbol mutators in macro universe
SI-6075 cleans up api.StandardNames
SI-6058 makes JavaMirror caches weak
SI-6111 accept single-subpattern unapply pattern
SI-4440 workaround: avoid outer accessor that'll vanish
SI-4881 infer variance from formals, then result
SI-6089 test file for pt2
Fix SI-6117, regression involving import ambiguity.
SI-6089 pt2: _ is tailpos in `_ || _` and `_ && _
SI-1832 consistent symbols in casedef's pattern&body
SI-5999 a real fix to the packageless problem
SI-6031 customizable budget for patmat analyses
SI-5999 removes the macro context mirror
SI-5999 deploys a new starr
SI-5999 removes Context.reify
SI-5984 improves error reporting in JavaMirrors
SI-4897 derive expected value from single type
Deprecate all JVM 1.5 targets and make 1.6 default.
SI-5784 Scaladoc: Type templates
Removes Float.Epsilon and Double.Epsilon
SI-5939 resident compilation of sources in empty package
SI-6104 support This pattern
Fixed SI-6092. Fixed leaky annotations, and relaxed the conditions under which a try-catch is lifted out to an inner method.
SI-6089 better tail position analysis for matches
SI-5695 removes Context.enclosingApplication
SI-5892 allow implicit views in annotation args
SI-6095, SI-6098 - clean up public API, add deprecations
SI-5739 store sub-patterns in local vals
SI-5731 a few fixes for value classes
Fixes SI-5588. Correct compare for Enumeration. Slower than the original one but does comparison in the same spirit as IntOrdering.
SI-5856 enables use of $this in string interpolation
SI-5895 fixes FieldMirrors
Fixed SI-6076. Range positions for macro-based string interpolation. Should bring back the jenkins job as well.
SI-5784 Scaladoc: {Abstract,Alias} type templates
test case closes SI-6047
Fix for SI-5385.
SI-6086 magic symbols strike back
Scaladoc: Refactoring the entities
SI-3695 SI-4224 SI-4497 SI-5079 scaladoc links
SI-4887 Link existentials in scaladoc
SI-4360 Adds prefixes to scaladoc
Scaladoc: workaround for untypical Map usecases
SI-4324 Scaladoc case class argument currying
SI-5558 Package object members indexing
SI-5965 Scaladoc crash
Scaladoc: Inherited templates in diagrams
SI-3314 SI-4888 Scaladoc: Relative type prefixes
SI-5235 Correct usecase variable expansion
SI-6035: Specialization and separate compilation.
SI-6011 switches: unreachability, guard-free form
SI-6028 Avoid needless symbol renaming in lambdalift.
A test case that scrutinises lambdalifter's output.
With -Yno-generic-signatures, exit GenASM.getGenericSignature early
SI-6077 more conservative TreeMakersToConds for CSE
SI-5956 trigger copy generation with correct namer
SI-5957 enable direct parsing of nested java class classfile
SI-6061 adds weakly conformance for number types to resolveOverloaded
SI-6022 model type-test-implication better
SI-6042 Improve type selection from volatile type error
Allow attachments for symbols, just like for trees.
Enhanced presentation compiler test infrastructure

New in Scala 2.9.2 Final (Jul 13, 2012)

New in Scala 2.9.1-1 Final (Mar 5, 2012)

New in Scala 2.10.0-M2 (Feb 22, 2012)

Support for implementing a parallel collection using a concurrent collection. In particular, one should be able to implement a combiner using a concurrent (thread-safe) collection.
Ctries added to the standard library. Implement parallel ctries using the above mechanism.
New futures and promises library added to scala.concurrent, joint work with the Akka team.
Numerous improvements to reification.
Virtual pattern matcher improvements -- please try compiling your project with -Yvirtpatmat, it will be on by default starting with 2.10.0-M3!
A significantly faster optimizer.
Improvements to RedBlack tree.
Fixes to specialization (AnyRef, interaction of final and @inline -- thank you, Erik Osheim!).
Closed tickets:
SI-4336 polymorphic expression isn't adapted to the expected type
SI-4835 scala.collection.immutable.StreamIterator[+A] has O(n) memory consumption
SI-5066 Predef.readLine(String, Any*) should call Console.readLine(text, args: _*) (Thank you, Szabolcs Berecz!)
SI-5215 Scalac crashes when I use @elidable for trait (Thank you, Szabolcs Berecz!)
SI-5224 Cannot reify @serializable class C
SI-5225 Bad reification of @transient @volatile var x = 2
SI-5229 Cannot reify objects
SI-5256 Classloading problems in REPL with Scala reflection
SI-5269 Cannot reify traits
SI-5270 Cannot reify self-types
SI-5271 Cannot reify case classes
SI-5272 Cannot reify simple pattern match
SI-5273 Cannot reify unapply-based pattern match
SI-5274 Cannot reify recursive functions
SI-5275 Cannot reify constructors with val-parameters
SI-5276 Cannot reify lazy vals
SI-5277 Cannot reify implicits
SI-5279 Cannot reify implicitly imported stuff from java.lang
SI-5287 Use case methods hide information about the actual method
SI-5293 Performance: Copying mutable.HashSet (FlatHashTable) 100x slower than java.util.HashSet.
SI-5334 Cannot reify code that returns an object of a locally defined type
SI-5335 Cannot reify anonymous classes
SI-5374 Deserialization of ListBuffer results in a non-mutable structure prone to throwing NoSuchElementException
SI-5375 Deadlock when parallel collection function throws an exception
SI-5405 Documentation error in scala.math.BigInt
SI-5419 Cannot reify 5: @Int
SI-5423 Mirror doesn't load annotations
SI-5429 object may override a def causing ClassCastException in unrelated code
SI-5444 Crash in LambdaLift
SI-5452 Stack overflow in doTypedApply when manifests meet overloads
SI-5497 undefined value leads to "no-symbol does not have an owner"
SI-5500 Strange type error with some AnyRef specializations (but not others)
SI-5506 cps errors with lists

New in Scala 2.9.0.1 (Jul 26, 2011)

Parallel Collections:
Every collection may be converted into a corresponding parallel collection with the new `par` method. Parallel collections utilize multicore processors by implementing bulk operations such as `foreach`, `map`, `filter` etc. in parallel. Parallel collections are located in the package `scala.collection.parallel`.
Depending on the collection in question, `par` may require copying the underlying dataset to create a parallel collection. However, specific collections share their underlying dataset with a parallel collection, making `par` a constant time operation.
Currently available parallel collections are -
parallel arrays - scala.collection.parallel.mutable.ParArray
parallel ranges - scala.collection.parallel.immutable.ParRange
parallel hash maps - scala.collection.parallel.mutable.ParHashMap
parallel hash sets - scala.collection.parallel.mutable.ParHashSet
parallel hash tries - scala.collection.parallel.immutable.{ParHashMap, ParHashSet}
parallel vectors - scala.collection.parallel.immutable.ParVector
The method `seq` is used to convert from a parallel collection to a corresponding sequential collection. This method is always efficient (O(1)).
The App Trait:
The App trait is a safer, more powerful alternative to the previous Application trait, which has now been deprecated. The new recommended way to write a top-level application is like this:
object Echo extends App {
println("Echo" + (args mkString " "))
Objects inheriting from the old Application trait were almost as convenient to write, but were not thread-safe and were often not optimized by the VM, since the application’s body was execited as part of of the object’s initialization sequence. Objects inheriting the App trait instead make use of Scala 2.9’s delayed initialization feature to execute the whole body as part of an inherited main method.
Another new feature of the App scheme is that command line arguments are now accessible via the args value (which is inherited from trait App)
The DelayedInit Trait
The DelayedInit trait provides another tool to customize initialization sequences of classes and objects. If a class or object inherits from this trait, all its initialization code is packed in a closure and forwarded as an argument to a method named delayedInit which is defined as an abstract method in trait DelayedInit.
Implementations of delayedInit have thus full freedom when to execute the initialization code. For instance, Scala’s new App trait stores all initialization sequences in an internal buffer and executes them when the object’s main method is called.
Note that only initialization code contained in classes and objects is passed to DelayedInit; initialization code contained in traits is not affected.
Repl Improvements
Improvements in jline, the repl input handler. More robust cursor handling, bash-style ctrl-R history search, new commands like :imports, :implicits, :keybindings. On platforms with the necessary runtime support, :javap will disassemble any class including repl-defined ones. A long-running repl command can now be interrupted via ctrl-C without terminating the repl session. Improved programmability: the repl classloader exposes repl-defined classes via their given names.
Scala Runner
Scala code can now be executed in any of the following ways -
scala will run the main class, similar to java -jar
scala will run the main method of that class
scala will run the script contents as a scala script
scala will, if the contents are not a script, find a single main method in a top level object and run that. This allows the same file to be used with scalac and to be run directly.
scala -save will create a jar file with the compiled source, which is then reusable and can be run as scala
Java Interop:
The @strictfp annotation is now supported.
Various fixes in JavaConverters and JavaConversions for smoother interoperation.
Primitive types and their boxed versions are now implicitly converted bidirectionally.
Other features:
Generalized try-catch-finally -
try body
catch handler
finally cleanup
Here, body and cleanup can be arbitrary expressions, and handler can be any expression which evaluates to a valid exception handler (which is: PartialFunction[Throwable, T]).
New packages
scala.sys and scala.sys.process, which are imported from sbt.Process.
New methods in collections
collectFirst, maxBy, minBy, span, inits, tails, permutations, combinations, subsets
AnyRef specialization
It’s now possible to specialize on type parameters for subtypes of AnyRef (class Foo[@specialize(AnyRef) T](arr: Array[T]) { … }), which allows for more efficient array indexing and updates.