Fix issue that prevented instantiating some tvars before implicit search

Author: smarter

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

@@ -141,7 +141,7 @@ object Inferencing {
       if (toTest.isEmpty) acc
       else tree match {
         case Apply(fn, _) =>
-          fn.tpe match {
+          fn.tpe.widen match {
             case mtp: MethodType =>
               val (occ, nocc) = toTest.partition(tvar => mtp.paramTypes.exists(tvar.occursIn))
               occurring(fn, nocc, occ ::: acc)

tests/pos/tparam_inf.scala

@@ -1,12 +1,38 @@
+class HasFoo[T] {
+  val x: Foo[T] = ???
+}
+class Foo[T] {
+  def get(x: T): T = x
+  def get2(x: T): Nothing = ???
+
+  def foo1(x: T)(implicit ev: T): Nothing = ???
+  def foo2(x: T)(implicit ev: T): T = ???
+  def foo3[Dummy](x: T)(implicit ev: T): Nothing = ???
+  def foo4[Dummy](x: T)(implicit ev: T): T = ???
+}
+
 object Test {
+
   def foo1[T](x: T)(implicit ev: T): Nothing = ???
   def foo2[T](x: T)(implicit ev: T): T = ???
 
-  def test: Unit = {
+  def test1: Unit = {
     implicit val ii: Int = 42
 
     foo1(10)
     foo2(10)
   }
-}
 
+  def hf[T]: HasFoo[T] = ???
+  def test2: Unit = {
+    implicit val ii: Int = 42
+
+    hf.x.get(10)
+    hf.x.get2(10)
+
+    hf.x.foo1(10)
+    hf.x.foo2(10)
+    hf.x.foo3(10)
+    hf.x.foo4(10)
+  }
+}