Switch mapping of context bounds to using clauses in 3.6 (#21257)

Was future before.

We can roll this out now, since we already made it an error in 3.5 to
pass a normal argument to a using clause. It would be good to roll this
out now since otherwise context bounds would represent an exception to
the implicit priority inversion in #19300.

See discussion at the end of #19300 for details.

Author: odersky

Diff for: community-build/community-projects/spire

@@ -300,7 +300,12 @@ object desugar {
       // implicit resolution in Scala 3.
 
     val paramssNoContextBounds =
-      val iflag = if Feature.sourceVersion.isAtLeast(`future`) then Given else Implicit
+      val iflag = paramss.lastOption.flatMap(_.headOption) match
+        case Some(param) if param.mods.isOneOf(GivenOrImplicit) =>
+          param.mods.flags & GivenOrImplicit
+        case _ =>
+          if Feature.sourceVersion.isAtLeast(`3.6`) then Given
+          else Implicit
       val flags = if isPrimaryConstructor then iflag | LocalParamAccessor else iflag | Param
       mapParamss(paramss) {
         tparam => desugarContextBounds(tparam, evidenceParamBuf, flags, freshName, paramss)
@@ -472,7 +477,14 @@ object desugar {
       case ValDefs(mparams) :: _ if mparams.exists(referencesBoundName) =>
         params :: mparamss
       case ValDefs(mparams @ (mparam :: _)) :: Nil if mparam.mods.isOneOf(GivenOrImplicit) =>
-        (params ++ mparams) :: Nil
+        val normParams =
+          if params.head.mods.flags.is(Given) != mparam.mods.flags.is(Given) then
+            params.map: param =>
+              val normFlags = param.mods.flags &~ GivenOrImplicit | (mparam.mods.flags & (GivenOrImplicit))
+              param.withMods(param.mods.withFlags(normFlags))
+                .showing(i"ADAPTED PARAM $result ${result.mods.flags} for ${meth.name}")
+          else params
+        (normParams ++ mparams) :: Nil
       case mparams :: mparamss1 =>
         mparams :: recur(mparamss1)
       case Nil =>

Diff for: compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -499,7 +499,7 @@ object Signatures {
 
     def isSyntheticEvidence(name: String) =
       name.startsWith(NameKinds.ContextBoundParamName.separator)
-      && symbol.paramSymss.flatten.find(_.name.show == name).exists(_.flags.is(Flags.Implicit))
+      && symbol.paramSymss.flatten.find(_.name.show == name).exists(_.flags.isOneOf(Flags.GivenOrImplicit))
 
     def toTypeParam(tpe: PolyType): List[Param] =
       val evidenceParams = (tpe.paramNamess.flatten zip tpe.paramInfoss.flatten).flatMap:

Diff for: compiler/src/dotty/tools/dotc/util/Signatures.scala

@@ -296,7 +296,7 @@ class ShortenedTypePrinter(
     val (methodParams, extParams) = splitExtensionParamss(gsym)
     val paramss = methodParams ++ extParams
     lazy val implicitParams: List[Symbol] =
-      paramss.flatMap(params => params.filter(p => p.is(Flags.Implicit)))
+      paramss.flatMap(params => params.filter(p => p.isOneOf(Flags.GivenOrImplicit)))
 
     lazy val implicitEvidenceParams: Set[Symbol] =
       implicitParams

Diff for: presentation-compiler/src/main/dotty/tools/pc/printer/ShortenedTypePrinter.scala

@@ -588,7 +588,8 @@ trait ClassLikeSupport:
         // `def foo[A: ClassTag] = 1`.
         // Scala spec states that `$` should not be used in names and behaviour may be undefiend in such case.
         // Documenting method slightly different then its definition is withing the 'undefiend behaviour'.
-        symbol.paramSymss.flatten.find(_.name == name).exists(_.flags.is(Flags.Implicit))
+        symbol.paramSymss.flatten.find(_.name == name).exists(p =>
+          p.flags.is(Flags.Given) || p.flags.is(Flags.Implicit))
 
     def handlePolyType(memberInfo: MemberInfo, polyType: PolyType): MemberInfo =
       val typeParamList = MemberInfo.TypeParameterList(polyType.paramNames.zip(polyType.paramBounds).toMap)

Diff for: scaladoc/src/dotty/tools/scaladoc/tasty/ClassLikeSupport.scala

@@ -3,7 +3,7 @@ scala> import quoted.staging.{Compiler => StagingCompiler, _}
 scala> implicit def compiler: StagingCompiler = StagingCompiler.make(getClass.getClassLoader)
 def compiler: scala.quoted.staging.Compiler
 scala> def fn[T : Type](v : T) = println("ok")
-def fn[T](v: T)(implicit evidence$1: scala.quoted.Type[T]): Unit
+def fn[T](v: T)(using evidence$1: scala.quoted.Type[T]): Unit
 scala> withQuotes { fn("foo") }
 ok
 scala> withQuotes { fn((1,2)) }

Diff for: staging/test-resources/repl-staging/i6263

@@ -0,0 +1,13 @@
+//> using options -source 3.5
+trait Eq[A]
+trait Order[A] extends Eq[A]:
+  def toOrdering: Ordering[A]
+
+def f[Element: Eq: Order] = summon[Eq[Element]].toOrdering // ok
+
+def Test() =
+  val eq: Eq[Int] = ???
+  val ord: Order[Int] = ???
+  f(eq, ord)  // error
+  f(using eq, ord) // ok
+

Diff for: tests/neg/ctx-bounds-priority-migration.scala

@@ -0,0 +1,6 @@
+//> using options -source 3.6
+trait Eq[A]
+trait Order[A] extends Eq[A]:
+  def toOrdering: Ordering[A]
+
+def Test[Element: Eq: Order] = summon[Eq[Element]].toOrdering // error

Diff for: tests/neg/ctx-bounds-priority.scala

@@ -1,23 +1,23 @@
 -- [E008] Not Found Error: tests/neg/i10901.scala:45:38 ----------------------------------------------------------------
 45 |    val pos1: Point2D[Int,Double] = x º y       // error
    |                                    ^^^
-   |       value º is not a member of object BugExp4Point2D.IntT.
-   |       An extension method was tried, but could not be fully constructed:
-   |
-   |           º(x)
-   |
-   |           failed with:
-   |
-   |               Ambiguous overload. The overloaded alternatives of method º in object dsl with types
-   |                [T1, T2]
-   |                 (x: BugExp4Point2D.ColumnType[T1])
-   |                   (y: BugExp4Point2D.ColumnType[T2])
-   |                     (implicit evidence$1: Numeric[T1], evidence$2: Numeric[T2]): BugExp4Point2D.Point2D[T1, T2]
-   |                [T1, T2]
-   |                 (x: T1)
-   |                   (y: BugExp4Point2D.ColumnType[T2])
-   |                     (implicit evidence$1: Numeric[T1], evidence$2: Numeric[T2]): BugExp4Point2D.Point2D[T1, T2]
-   |               both match arguments ((x : BugExp4Point2D.IntT.type))((y : BugExp4Point2D.DoubleT.type))
+   |          value º is not a member of object BugExp4Point2D.IntT.
+   |          An extension method was tried, but could not be fully constructed:
+   |
+   |              º(x)
+   |
+   |              failed with:
+   |
+   |                  Ambiguous overload. The overloaded alternatives of method º in object dsl with types
+   |                   [T1, T2]
+   |                    (x: BugExp4Point2D.ColumnType[T1])
+   |                      (y: BugExp4Point2D.ColumnType[T2])
+   |                        (using evidence$1: Numeric[T1], evidence$2: Numeric[T2]): BugExp4Point2D.Point2D[T1, T2]
+   |                   [T1, T2]
+   |                    (x: T1)
+   |                      (y: BugExp4Point2D.ColumnType[T2])
+   |                        (using evidence$1: Numeric[T1], evidence$2: Numeric[T2]): BugExp4Point2D.Point2D[T1, T2]
+   |                  both match arguments ((x : BugExp4Point2D.IntT.type))((y : BugExp4Point2D.DoubleT.type))
 -- [E008] Not Found Error: tests/neg/i10901.scala:48:38 ----------------------------------------------------------------
 48 |    val pos4: Point2D[Int,Double] = x º 201.1   // error
    |                                    ^^^
@@ -31,8 +31,8 @@
    |        Ambiguous overload. The overloaded alternatives of method º in object dsl with types
    |         [T1, T2]
    |          (x: BugExp4Point2D.ColumnType[T1])
-   |            (y: T2)(implicit evidence$1: Numeric[T1], evidence$2: Numeric[T2]): BugExp4Point2D.Point2D[T1, T2]
-   |         [T1, T2](x: T1)(y: T2)(implicit evidence$1: Numeric[T1], evidence$2: Numeric[T2]): BugExp4Point2D.Point2D[T1, T2]
+   |            (y: T2)(using evidence$1: Numeric[T1], evidence$2: Numeric[T2]): BugExp4Point2D.Point2D[T1, T2]
+   |         [T1, T2](x: T1)(y: T2)(using evidence$1: Numeric[T1], evidence$2: Numeric[T2]): BugExp4Point2D.Point2D[T1, T2]
    |        both match arguments ((x : BugExp4Point2D.IntT.type))((201.1d : Double))
 -- [E008] Not Found Error: tests/neg/i10901.scala:62:16 ----------------------------------------------------------------
 62 |  val y = "abc".foo  // error

Diff for: tests/neg/i10901.check

@@ -74,7 +74,7 @@ Trees (98 bytes, starting from <elided base index>):
     61:                 SHAREDtype 6
     63:             IDENTtpt 16 [T]
     65:               TYPEREFdirect 39
-    67:           IMPLICIT
+    67:           GIVEN
     68:         IDENTtpt 17 [Nothing]
     70:           TYPEREF 17 [Nothing]
     72:             TERMREFpkg 2 [scala]

Diff for: tests/pos/i20901/Foo.tastycheck

@@ -2621,9 +2621,9 @@ example/Methods#m6(+1). => method m6 (param x: List[T]): Nothing
 example/Methods#m6(+1).(x) => param x: List[T]
 example/Methods#m6(+2). => method m6 (param x: List[T]): Nothing
 example/Methods#m6(+2).(x) => param x: List[T]
-example/Methods#m7(). => method m7 [typeparam U ](param c: Methods[T], param l: List[U])(implicit param evidence$1: Ordering[U]): Nothing
+example/Methods#m7(). => method m7 [typeparam U ](param c: Methods[T], param l: List[U])(implicit given param evidence$1: Ordering[U]): Nothing
 example/Methods#m7().(c) => param c: Methods[T]
-example/Methods#m7().(evidence$1) => implicit param evidence$1: Ordering[U]
+example/Methods#m7().(evidence$1) => implicit given param evidence$1: Ordering[U]
 example/Methods#m7().(l) => param l: List[U]
 example/Methods#m7().[U] => typeparam U 
 example/Methods#m9(). => method m9 (param x: m9().): Nothing
@@ -3553,10 +3553,10 @@ example/Synthetic#F# => class F extends Object { self: F => +1 decls }
 example/Synthetic#F#`<init>`(). => primary ctor <init> (): F
 example/Synthetic#J# => class J [typeparam T ] extends Object { self: J[T] => +4 decls }
 example/Synthetic#J#[T] => typeparam T 
-example/Synthetic#J#`<init>`(). => primary ctor <init> [typeparam T ]()(implicit param evidence$1: Manifest[T]): J[T]
-example/Synthetic#J#`<init>`().(evidence$1) => implicit param evidence$1: Manifest[T]
+example/Synthetic#J#`<init>`(). => primary ctor <init> [typeparam T ](implicit given param evidence$1: Manifest[T])(): J[T]
+example/Synthetic#J#`<init>`().(evidence$1) => implicit given param evidence$1: Manifest[T]
 example/Synthetic#J#arr. => val method arr Array[T]
-example/Synthetic#J#evidence$1. => private[this] implicit val method evidence$1 Manifest[T]
+example/Synthetic#J#evidence$1. => private[this] implicit val given method evidence$1 Manifest[T]
 example/Synthetic#Name. => val method Name Regex
 example/Synthetic#`<init>`(). => primary ctor <init> (): Synthetic
 example/Synthetic#a1. => val method a1 Int