Bump scala-library from 2.12.4 to 2.13.4

[dependabot-preview]

Bumps scala-library from 2.12.4 to 2.13.4.

Release notes

Sourced from scala-library's releases.

Scala 2.13.4:

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

and more! Details below.

Concurrency

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

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

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

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

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

Pattern matching

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

The following types of matches no longer disable exhaustivity checking:

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

Additionally,

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

New warnings reported can be resolved by:

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

Commits

• 39148e4 mailmap updates
• 74cffdd Merge pull request #9318 from retronym/ticket/12227
• ca1cc4d Fix regressions in immutable.TreeMap merge errors from 2.12.x
• 1df410a Merge pull request #9296 from viktorklang/wip-opportunistic-√
• 0044904 Update scaladocs
• 8507cf0 Merge pull request #9312 from dwijnand/exhaust-nested-in-irrefutable
• 855b2a8 Patterns under irrefutable extractors are fixed
• a8d3741 Merge pull request #9308 from lrytz/merge-2.12-to-2.13-nov-9
• 2105dc7 Merge pull request #9306 from scalacenter/tasty/block-tuple
• 9ace1b1 Merge pull request #9307 from dotty-staging/fix-fun-sig
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #121.