Improve escape hatch for filter in generator

Allow `for (x @ (_: T) <- ts)` workaround using underscore as shown. Because the rewrite happens after patterns are transformed, it was taken as a straight typed pattern.
scala · Oct 31, 2020 · 68a6ae9 · 68a6ae9
1 parent 200c122
commit 68a6ae9
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Showing 2 changed files with 33 additions and 9 deletions.
diff --git a/src/reflect/scala/reflect/internal/TreeGen.scala b/src/reflect/scala/reflect/internal/TreeGen.scala
@@ -857,10 +857,11 @@ abstract class TreeGen {
    */
   private def matchVarPattern(tree: Tree): Option[(Name, Tree)] = {
     import nme.{WILDCARD => WC}
+    val forFor = tree.hasAttachment[ForAttachment.type]   // exclude user-written x @ _
     tree match {
-      case id @ Ident(name) if name.toTermName != WC || id.isBackquoted => Some((name, TypeTree()))
-      case Bind(name, Ident(x)) if x.toTermName == WC                   => Some((name, TypeTree()))
-      case Bind(name, Typed(Ident(x), tpt)) if x.toTermName == WC       => Some((name, tpt))
+      case id @ Ident(name) if name.toTermName != WC || id.isBackquoted             => Some((name, TypeTree()))
+      case Bind(name, Ident(x)) if forFor && x.toTermName == WC                     => Some((name, TypeTree()))
+      case Bind(name, Typed(Ident(x), tpt)) if forFor && x.toTermName == WC         => Some((name, tpt))
       case Typed(id @ Ident(name), tpt) if name.toTermName != WC || id.isBackquoted => Some((name, tpt))
       case _ => None
     }
@@ -934,15 +935,18 @@ abstract class TreeGen {
     override def transform(tree: Tree): Tree = tree match {
       case Ident(name) if treeInfo.isVarPattern(tree) && name != nme.WILDCARD =>
         atPos(tree.pos) {
-          val b = Bind(name, atPos(tree.pos.focus) (Ident(nme.WILDCARD)))
-          if (forFor && isPatVarWarnable) b updateAttachment NoWarnAttachment
-          else b
+          val b = Bind(name, atPos(tree.pos.focus) { Ident(nme.WILDCARD) })
+          if (forFor) {
+            b.updateAttachment(ForAttachment)
+            if (isPatVarWarnable) b.updateAttachment(NoWarnAttachment)
+          }
+          b
         }
       case Typed(id @ Ident(name), tpt) if treeInfo.isVarPattern(id) && name != nme.WILDCARD =>
         atPos(tree.pos.withPoint(id.pos.point)) {
-          Bind(name, atPos(tree.pos.withStart(tree.pos.point)) {
-            Typed(Ident(nme.WILDCARD), tpt)
-          })
+          val b = Bind(name, atPos(tree.pos.withStart(tree.pos.point)) { Typed(Ident(nme.WILDCARD), tpt) })
+          if (forFor) b.updateAttachment(ForAttachment)
+          b
         }
       case Apply(fn @ Apply(_, _), args) =>
         treeCopy.Apply(tree, transform(fn), transformTrees(args))

diff --git a/test/files/pos/t900-workaround.scala b/test/files/pos/t900-workaround.scala
@@ -0,0 +1,20 @@
+
+trait T {
+  val xs = Seq(Some(1), None)
+
+  def f() = for (x @ (_x: Some[_]) <- xs) yield x
+
+  def g() = for (x @ (_: Some[_]) <- xs) yield x
+}
+
+/*
+ * The second form was not translated to a partial function:
+  val res1 = xs.withFilter(((check$ifrefutable$1) => check$ifrefutable$1: @scala.unchecked match {
+    case (x @ (_: Some[(_ @ <empty>)])) => true
+    case _ => false
+  })).map(((x: Some[(_ @ <empty>)]) => x))
+ *
+ *        error: type mismatch;
+ *         found   : Some[_] => Some[Any]
+ *         required: Option[Int] => ?
+ */