Drop the requirement that extractors with get must implement Product

src/dotty/tools/dotc/typer/Applications.scala

@@ -51,9 +51,12 @@ object Applications {
     sels.takeWhile(_.exists).toList
   }
 
-  def getUnapplySelectors(tp: Type, args:List[untpd.Tree], pos: Position = NoPosition)(implicit ctx: Context): List[Type] =
-    if (defn.isProductSubType(tp) && args.length > 1) productSelectorTypes(tp, pos)
-    else tp :: Nil
+  def getUnapplySelectors(tp: Type, args: List[untpd.Tree], pos: Position = NoPosition)(implicit ctx: Context): List[Type] =
+    if (args.length > 1 && !(tp.derivesFrom(defn.SeqClass))) {
+      val sels = productSelectorTypes(tp, pos)
+      if (sels.length == args.length) sels
+      else tp :: Nil
+    } else tp :: Nil
 
   def unapplyArgs(unapplyResult: Type, unapplyFn:Tree, args:List[untpd.Tree], pos: Position = NoPosition)(implicit ctx: Context): List[Type] = {
 

tests/pos/extractors.scala

@@ -0,0 +1,32 @@
+object test {
+
+  class Tree
+  class Apply(val fun: Tree, val args: List[Tree]) extends Tree
+
+  trait DeconstructorCommon[T >: Null <: AnyRef] {
+    var field: T = null
+    def get: this.type = this
+    def isEmpty: Boolean = field eq null
+    def isDefined = !isEmpty
+    def unapply(s: T): this.type ={
+      field = s
+      this
+    }
+  }
+
+  trait ApplyDeconstructor extends DeconstructorCommon[Apply] {
+    def _1: Tree
+    def _2: List[Tree]
+  }
+
+  object Apply extends ApplyDeconstructor {
+    def _1: Tree = field.fun
+    def _2: List[Tree] = field.args
+  }
+
+  def assocsFromApply(tree: Tree) = {
+    tree match {
+      case Apply(fun, args) => ???
+    }
+  }
+}