Merge pull request #3484 from retronym/ticket/8237

SI-8237 Avoid cyclic constraints when inferring hk type args

3 files changed, 43 insertions, 1 deletions

diff --git a/test/files/neg/names-defaults-neg.check b/test/files/neg/names-defaults-neg.check
index 880ddc4327..20ddd55f1f 100644
--- a/test/files/neg/names-defaults-neg.check
+++ b/test/files/neg/names-defaults-neg.check
@@ -88,7 +88,7 @@ names-defaults-neg.scala:76: error: no type parameters for method test4: (x: T[T
  --- because ---
 argument expression's type is not compatible with formal parameter type;
  found   : List[Int]
- required: ?T
+ required: ?T[?T[List[?T[X forSome { type X }]]]]
 Error occurred in an application involving default arguments.
   test4()
   ^
diff --git a/test/files/neg/t8237-default.check b/test/files/neg/t8237-default.check
new file mode 100644
index 0000000000..59fe21ed03
--- /dev/null
+++ b/test/files/neg/t8237-default.check
@@ -0,0 +1,13 @@
+t8237-default.scala:5: error: no type parameters for method test4: (x: T[T[List[T[X forSome { type X }]]]])Nothing exist so that it can be applied to arguments (List[Int])
+ --- because ---
+argument expression's type is not compatible with formal parameter type;
+ found   : List[Int]
+ required: ?T[?T[List[?T[X forSome { type X }]]]]
+  test4(test4$default$1)
+  ^
+t8237-default.scala:5: error: type mismatch;
+ found   : List[Int]
+ required: T[T[List[T[X forSome { type X }]]]]
+  test4(test4$default$1)
+        ^
+two errors found
diff --git a/test/files/neg/t8237-default.scala b/test/files/neg/t8237-default.scala
new file mode 100644
index 0000000000..f695aa523f
--- /dev/null
+++ b/test/files/neg/t8237-default.scala
@@ -0,0 +1,29 @@
+// This test case was extracte from `names-defaults-neg.scala`
+// It pinpoints an improvement an error message that results from
+// a type inference failure
+object Test extends App {
+  test4(test4$default$1)
+
+  def test4[T[P]](x: T[T[List[T[X forSome { type X }]]]]) = ???
+  def test4$default$1[T[P]]: List[Int] = ???
+}
+
+/*
+OLD:
+ no type parameters for method test4: (x: T[T[List[T[X forSome { type X }]]]])Nothing exist so that it can be applied to arguments (List[Int])
+ --- because ---
+argument expression's type is not compatible with formal parameter type;
+ found   : List[Int]
+ required: ?T
+  test4(test4$default$1)
+  ^
+
+NEW:
+
+no type parameters for method test4: (x: T[T[List[T[X forSome { type X }]]]])Nothing exist so that it can be applied to arguments (List[Int])
+ --- because ---
+argument expression's type is not compatible with formal parameter type;
+ found   : List[Int]
+ required: ?T[?T[List[?T[X forSome { type X }]]]
+  test4(test4$default$1)
+*/