Add case-class-companion incompatibility

Author: adpi2

docs/incompatibilities/other-changed-features.md

@@ -26,3 +26,6 @@ title: Other Changed Features
 
 ```scala mdoc:file:incompat-30/wildcard-argument/README.md
 ```
+
+```scala mdoc:file:incompat-30/case-class-companion/README.md
+```

docs/incompatibilities/table.md

@@ -83,7 +83,7 @@ Some proven features are simplified or restricted to make the language easier an
 |[Non-private constructor in private class](other-changed-features.md#non-private-constructor-in-private-class)||warning|||
 |[Reflective call](other-changed-features.md#reflective-call)||||Type inference problem|
 |[Wildcard type argument](other-changed-features.md#wildcard-type-argument)|||||
-
+|[Case class companion](other-changed-features.md#case-class-companion)|||||
 
 ## Implicit Resolution
 

incompat-30/case-class-companion/README.md

@@ -0,0 +1,29 @@
+## Case class companion
+
+The companion object of a case class does not extend any of the `Function{0-23}` traits anymore.
+In particular, it does not inherit their methods: `tupled`, `curried`, `andThen`, `compose`...
+
+For instance, the following lines of code are invalid.
+
+```scala
+case class Foo(x: Int, b: Boolean)
+
+Foo.curried(1)(true)
+Foo.tupled((2, false))
+```
+
+A cross-compiling solution is to explicitly eta-expand the method `Foo.apply`.
+
+```scala
+(Foo.apply _).curried(1)(true)
+(Foo.apply _).tupled((2, false))
+```
+
+Or, for performance reason, you can introduce an intermediate function value.
+
+```scala
+val fooCtr: (Int, Boolean) => Foo = (x, b) => Foo(x, b)
+
+fooCtr.curried(1)(true)
+fooCtr.tupled((2, false))
+```

incompat-30/case-class-companion/src/main/scala-2.13/case-class-companion.scala

@@ -0,0 +1,8 @@
+package foo
+
+case class Foo(x: Int, b: Boolean)
+
+object Bar {
+  val f1 = Foo.curried(1)(true)
+  val f2 = Foo.tupled((2, false))
+}

incompat-30/case-class-companion/src/main/scala/case-class-companion.scala

@@ -0,0 +1,13 @@
+package foo
+
+case class Foo(x: Int, b: Boolean)
+
+object Bar {
+  val f1 = (Foo.apply _).curried(1)(true)
+  val f2 = (Foo.apply _).tupled((1, true))
+
+  val fooCtr: (Int, Boolean) => Foo = (x, b) => Foo(x, b)
+
+  val f1Bis = fooCtr.curried(1)(true)
+  val f2Bis = fooCtr.tupled((2, false))
+}

incompat.sbt

@@ -152,7 +152,8 @@ lazy val otherIncompats = Seq[ProjectReference](
   ambiguousConversion,
   implicitView,
   typeOfImplicitDef,
-  viewBound
+  viewBound,
+  caseClassCompanion
 )
 
 // Syntactic incompatibilities
@@ -172,6 +173,7 @@ lazy val existentialType = project.in(file("incompat-30/existential-type")).sett
 lazy val wildcardArgument = project.in(file("incompat-30/wildcard-argument")).settings(incompat30Settings)
 lazy val explicitCallToUnapply = project.in(file("incompat-30/explicit-call-to-unapply")).settings(incompat30Settings)
 lazy val reflectiveCall = project.in(file("incompat-30/reflective-call")).settings(incompat30Settings)
+lazy val caseClassCompanion = project.in(file("incompat-30/case-class-companion")).settings(incompat30Settings)
 
 // Contextual abstraction incompatibilities
 lazy val ambiguousConversion =