Make -> sugar an inline method

Must wait for 3.10.0

currently it is transparent inline, to avoid inline proxy objects appearing in capture sets and breaking type checking.

Author: bishabosha

library/src/scala/Predef.scala

@@ -389,7 +389,9 @@ object Predef extends LowPriorityImplicits {
   // implicit classes -----------------------------------------------------
 
   /** @group implicit-classes-any */
+  @deprecated("Use `->` extension method instead.", since = "3.10.0")
   implicit final class ArrowAssoc[A](private val self: A) extends AnyVal {
+    @deprecated("Use `->` extension method instead.", since = "3.10.0")
     @inline def -> [B](y: B): (A, B) = (self, y)
     @deprecated("Use `->` instead. If you still wish to display it as one character, consider using a font with programming ligatures such as Fira Code.", "2.13.0")
     def →[B](y: B): (A, B) = ->(y)
@@ -609,6 +611,11 @@ object Predef extends LowPriorityImplicits {
      */
     inline def runtimeChecked: x.type @RuntimeChecked = x: @RuntimeChecked
 
+  // extension method sugar ---------------------------------------------
+  extension[A] (self: A)
+    transparent inline def -> [B](y: B): (A, B) = (self, y)
+
+
 }
 
 /** The `LowPriorityImplicits` class provides implicit values that

presentation-compiler/test/dotty/tools/pc/tests/completion/CompletionExtensionSuite.scala

@@ -453,6 +453,7 @@ class CompletionExtensionSuite extends BaseCompletionSuite:
       """|baz(): Unit
          |copy(): Bar
          |qux: Unit
+         |->[B](y: B): (Bar, B)
          |asInstanceOf[X0]: X0
          |canEqual(that: Any): Boolean
          |equals(x$0: Any): Boolean
@@ -467,7 +468,6 @@ class CompletionExtensionSuite extends BaseCompletionSuite:
          |productPrefix: String
          |synchronized[X0](x$0: X0): X0
          |toString(): String
-         |->[B](y: B): (Bar, B)
          |ensuring(cond: Boolean): Bar
          |ensuring(cond: Bar => Boolean): Bar
          |ensuring(cond: Boolean, msg: => Any): Bar

presentation-compiler/test/dotty/tools/pc/tests/completion/CompletionSuite.scala

@@ -109,6 +109,7 @@ class CompletionSuite extends BaseCompletionSuite:
          |tabulate[A](n: Int)(f: Int => A): List[A]
          |unapplySeq[A](x: List[A] @uncheckedVariance): UnapplySeqWrapper[A]
          |unfold[A, S](init: S)(f: S => Option[(A, S)]): List[A]
+         |->[B](y: B): (List.type, B)
          |fromSpecific(from: Any)(it: IterableOnce[Nothing]): List[Nothing]
          |fromSpecific(it: IterableOnce[Nothing]): List[Nothing]
          |toFactory(from: Any): Factory[Nothing, List[Nothing]]
@@ -120,7 +121,6 @@ class CompletionSuite extends BaseCompletionSuite:
          |isInstanceOf[X0]: Boolean
          |synchronized[X0](x$0: X0): X0
          |toString(): String
-         |->[B](y: B): (List.type, B)
          |ensuring(cond: Boolean): List.type
          |ensuring(cond: List.type => Boolean): List.type
          |ensuring(cond: Boolean, msg: => Any): List.type

tests/run-staging/i5965.check

@@ -11,7 +11,7 @@ List(1, 2, 3)
 }
 Some(4)
 {
-  val y: [V >: scala.Nothing <: scala.Any] =>> scala.collection.immutable.Map[scala.Int, V][scala.Int] = scala.Predef.Map.apply[scala.Int, scala.Int](scala.Predef.ArrowAssoc[scala.Int](4).->[scala.Int](1))
+  val y: [V >: scala.Nothing <: scala.Any] =>> scala.collection.immutable.Map[scala.Int, V][scala.Int] = scala.Predef.Map.apply[scala.Int, scala.Int](scala.Predef.->[scala.Int](4)[scala.Int](1))
 
   (y: scala.collection.immutable.Map[scala.Int, scala.Int])
 }

tests/run-staging/i5965b.check

@@ -11,7 +11,7 @@ List(1, 2, 3)
 }
 Some(4)
 {
-  val y: scala.collection.immutable.Map[scala.Int, scala.Int] = scala.Predef.Map.apply[scala.Int, scala.Int](scala.Predef.ArrowAssoc[scala.Int](4).->[scala.Int](1))
+  val y: scala.collection.immutable.Map[scala.Int, scala.Int] = scala.Predef.Map.apply[scala.Int, scala.Int](scala.Predef.->[scala.Int](4)[scala.Int](1))
 
   (y: scala.collection.immutable.Map[scala.Int, scala.Int])
 }

tests/semanticdb/expect/Synthetic.expect.scala

@@ -17,7 +17,7 @@ class Synthetic/*<-example::Synthetic#*/ {
 
   val lst/*<-example::Synthetic#lst.*/ = 1 #:: 2 #:: LazyList/*->scala::package.LazyList.*/.empty/*->scala::collection::immutable::LazyList.empty().*/
 
-  for (x/*<-local0*/ <- 1 to/*->scala::runtime::RichInt#to().*/ 10; y/*<-local1*/ <- 0 until/*->scala::runtime::RichInt#until().*/ 10) println/*->scala::Predef.println(+1).*/(x/*->local0*/ ->/*->scala::Predef.ArrowAssoc#`->`().*/ x/*->local0*/)
+  for (x/*<-local0*/ <- 1 to/*->scala::runtime::RichInt#to().*/ 10; y/*<-local1*/ <- 0 until/*->scala::runtime::RichInt#until().*/ 10) println/*->scala::Predef.println(+1).*/(x/*->local0*/ ->/*->scala::Predef.`->`().*/ x/*->local0*/)
   for (i/*<-local2*/ <- 1 to/*->scala::runtime::RichInt#to().*/ 10; j/*<-local3*/ <- 0 until/*->scala::runtime::RichInt#until().*/ 10) yield (i/*->local2*/, j/*->local3*/)
   for (i/*<-local4*/ <- 1 to/*->scala::runtime::RichInt#to().*/ 10; j/*<-local5*/ <- 0 until/*->scala::runtime::RichInt#until().*/ 10 if i/*->local4*/ %/*->scala::Int#`%`(+3).*/ 2 ==/*->scala::Int#`==`(+3).*/ 0) yield (i/*->local4*/, j/*->local5*/)
 

tests/semanticdb/metac.expect

@@ -3838,7 +3838,7 @@ Language => Scala
 Symbols => 62 entries
 Occurrences => 165 entries
 Diagnostics => 4 entries
-Synthetics => 48 entries
+Synthetics => 47 entries
 
 Symbols:
 example/Synthetic# => class Synthetic extends Object { self: Synthetic => +23 decls }
@@ -3944,7 +3944,7 @@ Occurrences:
 [19:28..19:33): until -> scala/runtime/RichInt#until().
 [19:38..19:45): println -> scala/Predef.println(+1).
 [19:46..19:47): x -> local0
-[19:48..19:50): -> -> scala/Predef.ArrowAssoc#`->`().
+[19:48..19:50): -> -> scala/Predef.`->`().
 [19:51..19:52): x -> local0
 [20:7..20:8): i <- local2
 [20:14..20:16): to -> scala/runtime/RichInt#to().
@@ -4104,8 +4104,7 @@ Synthetics:
 [17:24..17:38):LazyList.empty => *[Nothing]
 [19:12..19:13):1 => intWrapper(*)
 [19:26..19:27):0 => intWrapper(*)
-[19:46..19:50):x -> => *[Int]
-[19:46..19:47):x => ArrowAssoc[Int](*)
+[19:48..19:50):-> => *[Int]
 [20:12..20:13):1 => intWrapper(*)
 [20:26..20:27):0 => intWrapper(*)
 [20:44..20:50):(i, j) => Tuple2.apply[Int, Int](*)