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