Adress review comments with changed docs and new tests

Author: odersky

docs/_docs/reference/experimental/typeclasses.md

@@ -1,12 +1,9 @@
-
 ---
 layout: doc-page
-title: "Type Classes"
+title: "Better Support for Type Classes"
 nightlyOf: https://docs.scala-lang.org/scala3/reference/experimental/typeclasses.html
 ---
 
-# Some Proposed Changes for Better Support of Type Classes
-
 Martin Odersky, 8.1.2024, edited 5.4.2024
 
 A type class in Scala is a pattern where we define

tests/neg/deferred-givens-2.check

@@ -0,0 +1,12 @@
+-- [E172] Type Error: tests/neg/deferred-givens-2.scala:17:6 -----------------------------------------------------------
+17 |class SortedIntWrong1 extends Sorted: // error
+   |^
+   |No given instance of type Ord{type Self = SortedIntWrong1.this.Element} was found for inferring the implementation of the deferred given instance given_Ord_Element in trait Sorted
+18 |  type Element = Int
+19 |  override given (Element is Ord)()
+-- [E172] Type Error: tests/neg/deferred-givens-2.scala:21:6 -----------------------------------------------------------
+21 |class SortedIntWrong2 extends Sorted: // error
+   |^
+   |No given instance of type Ord{type Self = SortedIntWrong2.this.Element} was found for inferring the implementation of the deferred given instance given_Ord_Element in trait Sorted
+22 |  type Element = Int
+23 |  override given (Int is Ord)()

tests/neg/deferred-givens-2.scala

@@ -0,0 +1,23 @@
+//> using options -language:experimental.modularity -source future
+trait Ord:
+  type Self
+
+trait Sorted:
+  type Element: Ord
+
+object Scoped:
+  given (Int is Ord)()
+  class SortedIntCorrect extends Sorted:
+    type Element = Int
+
+class SortedIntCorrect2 extends Sorted:
+  type Element = Int
+  override given (Int is Ord)() as given_Ord_Element
+
+class SortedIntWrong1 extends Sorted: // error
+  type Element = Int
+  override given (Element is Ord)()
+
+class SortedIntWrong2 extends Sorted: // error
+  type Element = Int
+  override given (Int is Ord)()

tests/pending/pos/cbproxy-default.scala

@@ -0,0 +1,4 @@
+def f[S: Monad](
+  initial: S.Self = S.unit // error
+) =
+  S.unit // works

tests/pending/pos/singleton-infer.scala

@@ -0,0 +1,8 @@
+//> using options -Xprint:typer -language:experimental.modularity -source future
+
+def f1[S, T <: S : Singleton](x: S) = ()
+def f2[S, T >: S : Singleton](x: S) = ()
+
+def Test =
+  f1(42) // f1[Int, Singleton & Int] // should infer (42 : Int) or throw an error?
+  f2(42) // f2[(42 : Int), (42 : Int)]

tests/pos/cbproxy-expansion.scala

@@ -0,0 +1,16 @@
+//> using options -language:experimental.modularity -source future
+trait TC[T]:
+  type Self
+
+def f1[S, T: TC[S] as tc](x: S, y: tc.Self) = ()
+def f2[S, T: TC[S]](x: S, y: T.Self) = ()
+def f3[S, T: TC[S]](x: S, y: Int) = ()
+
+given TC[String] with
+  type Self = Int
+  def unit = 42
+
+def main =
+  f1("hello", 23)
+  f2("hello", 23)
+  f3("hello", 23)