Add section on vararg patterns

Author: odersky

docs/docs/reference/changed/lazy-vals.md

@@ -4,7 +4,7 @@ title: Changed: Lazy Vals and @volatile
 ---
 
 Lazy val initialization no longer guarantees safe publishing. This change was done
-to avid the performance overhead of thread synchonization because many lazy vals are only used in a single-threaded context.
+to avoid the performance overhead of thread synchonization because many lazy vals are only used in a single-threaded context.
 
 To get back safe publishing you need to annotate a lazy val with `@volatile`. In
 
@@ -14,6 +14,6 @@ it is guaranteed that readers of a lazy val will see the value of `x`
 once it is assigned.
 
 The [ScalaFix](https://scalacenter.github.io/scalafix/) rewrite tool
-as well as Dotty's own `-migration` option will rewrite all normal
+as well as Dotty's own `-language:Scala2 -rewrite` option will rewrite all normal
 lazy vals to volatile ones in order to keep their semantics compatible
 with current Scala's.

docs/docs/reference/changed/vararg-patterns.md

@@ -0,0 +1,21 @@
+---
+layout: doc-page
+title: "Vararg Patterns"
+---
+
+The syntax of vararg patterns has changed. In the new syntax one
+writes varargs in patterns exactly like one writes them in
+expressions, using a `: _*` type annotation:
+
+    xs match {
+      case List(1, 2, xs: _*) => println(xs)    // binds xs
+      case List(1, _ : _*) =>                   // wildcard pattern
+    }
+
+The old syntax, which is shorter but less regular, is no longer
+supported:
+
+    /*!*/ case List(1, 2, xs @ _*)       // syntax error
+    /*!*/ case List(1, 2, _*) => ...     // syntax error
+
+

docs/sidebar.yml

@@ -47,6 +47,8 @@ sidebar:
               url: docs/reference/changed/type-inference.md
             - title: Implicit Resolution
               url: docs/reference/changed/implicit-resolution.md
+            - title: Vararg Patterns
+              url: docs/reference/changed/vararg-patterns.md
         - title: Dropped Features
           subsection:
             - title: DelayedInit

tests/pos/reference/vararg-patterns.scala

@@ -0,0 +1,6 @@
+package varargPatterns
+object t1 extends App {
+  val List(1, 2, xs : _*) = List(1, 2, 3)
+  println(xs)
+  val List(1, 2, _ : _*) = List(1, 2, 3)
+}