Fix desugaring of Bind(WILDCARD, _).

src/dotty/tools/dotc/ast/Desugar.scala

@@ -1007,8 +1007,8 @@ object desugar {
     def add(named: NameTree, t: Tree): Unit =
       if (!seenName(named.name)) buf += ((named, t))
     def collect(tree: Tree): Unit = tree match {
-      case Bind(nme.WILDCARD, _) =>
-        collect(tree)
+      case Bind(nme.WILDCARD, tree1) =>
+        collect(tree1)
       case tree @ Bind(_, Typed(tree1, tpt)) if !mayBeTypePat(tpt) =>
         add(tree, tpt)
         collect(tree1)

tests/pos/i1432.scala

@@ -0,0 +1,3 @@
+object Foo {
+  val _@a = 1 // This entered in an infinite loop
+}

tests/run/i1432.check

@@ -0,0 +1,2 @@
+Some(foo)
+foo

tests/run/i1432.scala

@@ -0,0 +1,11 @@
+object Test {
+
+  def main(args: Array[String]): Unit = {
+    val someFoo = Some("foo")
+    val _ @ bar = someFoo
+    val _ @ Some(baz) = someFoo
+    println(bar)
+    println(baz)
+  }
+
+}