[Scala 3] port ApplierUnapplier (Mirror-based)#881
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halotukozak merged 4 commits intoJun 16, 2026
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Verbatim port from origin/master:core/src/main/scala-3/com/avsystem/commons/misc/ApplierUnapplier.scala.
Reshapes the Scala 2 macro `materialize` resolver into Scala 3 `given derived` typeclass derivation
based on `scala.deriving.Mirror.ProductOf`:
- Applier: given derived[T <: Product: Mirror.ProductOf as m]
- Unapplier: given derived[T <: Product] (productIterator-based)
- ApplierUnapplier: given derived[T: {Applier as applier, Unapplier as unapplier}]
Public trait surface (Applier / Unapplier / ApplierUnapplier / ProductUnapplier /
ProductApplierUnapplier) unchanged. Removes the `implicit def materialize[T] = ???` stubs left over
from Phase-1 big-bang. Added `import scala.deriving.Mirror` (CommonAliases export sweep is slice-3.x
territory; minimum local diff here). Local scalafmt applied.
ApplierUnapplierTest is exercised by the Mirror-based derivation since fork commit 7085bd8
re-enabled the test file; un-wrap follow-up commit will sync our copy.
Refs: APPLIERUNAPPLIER-01.
Sync test file with fork (origin/master:core/src/test/scala-3/com/avsystem/commons/misc/ApplierUnapplierTest.scala). Fork re-enabled this test at commit 7085bd8. Diff vs prior local copy: - trailing comma after `value: T` parameter (scalafmt scala3 dialect) - `test("custom") { roundtrip(Custom("", 42)) }` → `ignore("custom") { /* ... */ }` rationale documented in test comment: Mirror.ProductOf only fires for true case classes, not "case-class-like" types with hand-written apply/unapply. All 7 active cases green (`commons-core/testOnly *.ApplierUnapplierTest`), 1 ignored. Local scalafmt applied.
§3 new subsection "core — misc ApplierUnapplier (slice 5.3)" documenting the macro→Mirror.ProductOf
reshape: public Applier/Unapplier/ApplierUnapplier traits preserved; resolution mechanism flipped
from Scala 2 `implicit def materialize[T] = macro …` to Scala 3 `given derived[T <: Product:
Mirror.ProductOf as m]` / `given derived[T: {Applier as applier, Unapplier as unapplier}]`.
ApplierUnapplierTest re-enabled per fork commit 7085bd8; the `custom` case is `ignore`d because
Mirror.ProductOf only fires for true case classes/tuples, not hand-written "case-class-like" types.
Backlog: removed three stale rows for ApplierUnapplier.scala lines 13/25/37 (Applier.materialize,
Unapplier.materialize, ApplierUnapplier.materialize).
Refs: APPLIERUNAPPLIER-01.
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halotukozak
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June 2, 2026 12:39
| object ApplierUnapplier { | ||
| // TODO[scala3-port]: ApplierUnapplier.materialize (Scala 2 macro def) (L) | ||
| implicit def materialize[T]: ApplierUnapplier[T] = ??? | ||
| given derived[T: {Applier as applier, Unapplier as unapplier}]: ApplierUnapplier[T] = new ApplierUnapplier[T] { |
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Named context bounds in complex form like (T: {A as a, B as b}) is Scala 3.6+ feature - dont we want to support LTS 3.3 ? FYL LTS 3.9 is said to loose compatibility with scala 2
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we won't use it compatibility either way (because this library I macro-heavy). It would be better to have almost identical sources (in scala-2 and scala-3) with the copied content rather than one cross compiled, because we can use scala 3 features more freely, we can get used to scala 3 syntax, and our code will benefit and don't require another breaking change in the future (for example, we can replace implicit classes with extensions already, which have much better perf)
…ame `WithOpt` to `WithOption`.
Andrzej-Swietek
approved these changes
Jun 15, 2026
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LGTM |
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Restores
misc.ApplierUnapplierfamily from Phase-1???stubs to real Scala 3 typeclass implementations backed byscala.deriving.Mirror.ProductOf. Cribbed verbatim from forkorigin/master:core/src/main/scala-3/com/avsystem/commons/misc/ApplierUnapplier.scala.What's restored
Applier[T <: Product]—Seq[Any] => TviaMirror.ProductOf[T] + Tuple.fromArray.Unapplier[T <: Product]—T => Seq[Any]viaproductIterator.ApplierUnapplier[T]— combined.ProductUnapplier[T]/ProductApplierUnapplier[T]— concrete/abstract base classes for downstream extension.All four use Scala 3
given derivedwith@implicitNotFoundmessages preserved.Tests
Restored
ApplierUnapplierTest(was wrapped in Phase 1). Expanded coverage beyond the fork:Empty,Single,Multiple,Varargs,Generic,Over22(>22 params),tuple.Optionfield,assertDoesNotCompilefor sealed traits,ProductApplierUnappliersubclass usage, standaloneApplier/Unappliersummoning.ignore("custom")stub — Mirror only derives for actual case classes, hand-writtenapply/unapplyis out of scope.Over22default valuesp14/p19/p20were copy-paste typos ("13"/"18"/"18").12/12 tests green, 0 ignored.
MIGRATION.md
§3 core — misc ApplierUnapplierentry; backlog rows for the threematerializeScala 2 macro stubs removed.Slice 5.3 / Phase 5 leaf-feature-restoration.