Merge pull request #4034 from dotty-staging/fix-4030

Fix #4030: avoid adding duplicate binders

Author: liufengyun

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

@@ -910,8 +910,10 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
     /** Add a `Bind` node for each `bound` symbol in a type application `unapp` */
     def addBinders(unapp: Tree, bound: List[Symbol]) = unapp match {
       case TypeApply(fn, args) =>
+        var remain = bound.toSet
         def addBinder(arg: Tree) = arg.tpe.stripTypeVar match {
-          case ref: TypeRef if bound.contains(ref.symbol) =>
+          case ref: TypeRef if remain.contains(ref.symbol) =>
+            remain -= ref.symbol
             tpd.Bind(ref.symbol, Ident(ref))
           case _ =>
             arg

tests/patmat/i4030.check

@@ -0,0 +1 @@
+9: Pattern Match Exhaustivity: (C4(), _), (_, C4())

tests/patmat/i4030.scala

@@ -0,0 +1,13 @@
+sealed trait Root[T]
+case object C1 extends Root[Int]
+case object C2 extends Root[String]
+case class C3[X, Y]() extends Root[(X => X)|(Y => Y)|(X => Y)]
+case class C4[X, Y]() extends Root[(X => X)|(Y => Y)|(X => Y)]
+
+object TestGADT {
+
+  def f[A <: Seq[_], B, Foo >: A => B](v: Root[Foo], u: Root[Foo]) = (v, u) match {
+    case (C3(), C3()) =>
+  }
+  f(C3[Seq[_], Long](), C4[Seq[_], Long]())
+}