Refinements to auto tupling

There's a nasty interaction with auto-tupling and trying to insert an implicit
on the qualifier of a call. If the original call fails, we need to "undo" any
auto-tupling decisions in calls where an implicit is inserted on the qualifier.

Also: Needed to fix canAutoTuple test so that Scala2 feature is checked instead of dotty's.

Also: Drop features in dotty.language that duplicate those in scala.language.

6 files changed, 59 insertions, 31 deletions

diff --git a/src/dotty/language.scala b/src/dotty/language.scala
index 96250a9f2..0ed75bd26 100644
--- a/src/dotty/language.scala
+++ b/src/dotty/language.scala
@@ -4,13 +4,9 @@ object language {
 
   class Feature
 
-  /** Allow higher-kinded type syntax (not yet checked) */
-  val higherKinds = new Feature
-
   /** Keep union types */
   val keepUnions = new Feature
 
-  /** No auto tupling */
-  val noAutoTupling = new Feature
+  val f = "".contains("", (_: Int))
 
 }
diff --git a/src/dotty/tools/dotc/core/TypeOps.scala b/src/dotty/tools/dotc/core/TypeOps.scala
index 93b1b1f02..b69ce2536 100644
--- a/src/dotty/tools/dotc/core/TypeOps.scala
+++ b/src/dotty/tools/dotc/core/TypeOps.scala
@@ -493,7 +493,7 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
    */
   def featureEnabled(owner: ClassSymbol, feature: TermName): Boolean = {
     def toPrefix(sym: Symbol): String =
-      if (!sym.exists || (sym eq defn.LanguageModuleClass) || (sym eq defn.Scala2LanguageModuleRef)) ""
+      if (!sym.exists || (sym eq defn.LanguageModuleClass) || (sym eq defn.Scala2LanguageModuleClass)) ""
       else toPrefix(sym.owner) + sym.name + "."
     def featureName = toPrefix(owner) + feature
     def hasImport(implicit ctx: Context): Boolean = {
@@ -512,7 +512,7 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
 
   /** Is auto-tupling enabled? */
   def canAutoTuple =
-    !featureEnabled(defn.LanguageModuleClass, nme.noAutoTupling)
+    !featureEnabled(defn.Scala2LanguageModuleClass, nme.noAutoTupling)
 
   def scala2Mode =
     featureEnabled(defn.LanguageModuleClass, nme.Scala2)
diff --git a/src/dotty/tools/dotc/typer/Applications.scala b/src/dotty/tools/dotc/typer/Applications.scala
index c8f41b7fa..efd12cb5e 100644
--- a/src/dotty/tools/dotc/typer/Applications.scala
+++ b/src/dotty/tools/dotc/typer/Applications.scala
@@ -541,17 +541,29 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
 
   def typedApply(tree: untpd.Apply, pt: Type)(implicit ctx: Context): Tree = {
 
+    /** Try same application with an implicit inserted around the qualifier of the function
+     *  part. Return an optional value to indicate success.
+     */
+    def tryWithImplicitOnQualifier(fun1: Tree, proto: FunProto)(implicit ctx: Context): Option[Tree] =
+      tryInsertImplicitOnQualifier(fun1, proto) flatMap { fun2 =>
+        tryEither { implicit ctx =>
+          Some(typedApply(
+            cpy.Apply(tree)(untpd.TypedSplice(fun2), proto.typedArgs map untpd.TypedSplice),
+            pt)): Option[Tree]
+        } { (_, _) => None }
+     }
+
     def realApply(implicit ctx: Context): Tree = track("realApply") {
-      var proto = new FunProto(tree.args, IgnoredProto(pt), this)(argCtx(tree))
-      val fun1 = typedExpr(tree.fun, proto)
+      val originalProto = new FunProto(tree.args, IgnoredProto(pt), this)(argCtx(tree))
+      val fun1 = typedExpr(tree.fun, originalProto)
 
-      // Warning: The following line is dirty and fragile. We record that auto-tupling was demanded as
+      // Warning: The following lines are dirty and fragile. We record that auto-tupling was demanded as
       // a side effect in adapt. If it was, we assume the tupled proto-type in the rest of the application.
       // This crucially relies on he fact that `proto` is used only in a single call of `adapt`,
       // otherwise we would get possible cross-talk between different `adapt` calls using the same
       // prototype. A cleaner alternative would be to return a modified prototype from `adapt` together with
       // a modified tree but this would be more convoluted and less efficient.
-      if (proto.isTupled) proto = proto.tupled
+      val proto = if (originalProto.isTupled) originalProto.tupled else originalProto
 
       // If some of the application's arguments are function literals without explicitly declared
       // parameter types, relate the normalized result type of the application with the
@@ -580,13 +592,11 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
               val result = app.result
               convertNewGenericArray(ConstFold(result))
             } { (failedVal, failedState) =>
-              val fun2 = tryInsertImplicitOnQualifier(fun1, proto)
-              if (fun1 eq fun2) {
-                failedState.commit()
-                failedVal
-              } else typedApply(
-                cpy.Apply(tree)(untpd.TypedSplice(fun2), proto.typedArgs map untpd.TypedSplice), pt)
-            }
+              def fail = { failedState.commit(); failedVal }
+              tryWithImplicitOnQualifier(fun1, originalProto).getOrElse(
+                if (proto eq originalProto) fail
+                else tryWithImplicitOnQualifier(fun1, proto).getOrElse(fail))
+             }
           case _ =>
             handleUnexpectedFunType(tree, fun1)
         }
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index 2b690ef51..34cd5448b 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -1445,26 +1445,27 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       val sel = typedSelect(untpd.Select(untpd.TypedSplice(tree), nme.apply), pt)
       if (sel.tpe.isError) sel else adapt(sel, pt)
     } { (failedTree, failedState) =>
-      val tree1 = tryInsertImplicitOnQualifier(tree, pt)
-      if (tree1 eq tree) fallBack(failedTree, failedState)
-      else adapt(tree1, pt)
-    }
+      tryInsertImplicitOnQualifier(tree, pt) match {
+        case Some(tree1) => adapt(tree1, pt)
+        case none => fallBack(failedTree, failedState)
+      }
+     }
 
   /** If this tree is a select node `qual.name`, try to insert an implicit conversion
    *  `c` around `qual` so that `c(qual).name` conforms to `pt`. If that fails
    *  return `tree` itself.
    */
-  def tryInsertImplicitOnQualifier(tree: Tree, pt: Type)(implicit ctx: Context): Tree = ctx.traceIndented(i"try insert impl on qualifier $tree $pt") {
+  def tryInsertImplicitOnQualifier(tree: Tree, pt: Type)(implicit ctx: Context): Option[Tree] = ctx.traceIndented(i"try insert impl on qualifier $tree $pt") {
     tree match {
       case Select(qual, name) =>
         val qualProto = SelectionProto(name, pt, NoViewsAllowed)
         tryEither { implicit ctx =>
           val qual1 = adaptInterpolated(qual, qualProto, EmptyTree)
-          if ((qual eq qual1) || ctx.reporter.hasErrors) tree
-          else typedSelect(cpy.Select(tree)(untpd.TypedSplice(qual1), name), pt)
-        } { (_, _) => tree
+          if ((qual eq qual1) || ctx.reporter.hasErrors) None
+          else Some(typedSelect(cpy.Select(tree)(untpd.TypedSplice(qual1), name), pt))
+        } { (_, _) => None
         }
-      case _ => tree
+      case _ => None
     }
   }
 
diff --git a/tests/neg/autoTuplingTest.scala b/tests/neg/autoTuplingTest.scala
index 37136b760..62f10b3ea 100644
--- a/tests/neg/autoTuplingTest.scala
+++ b/tests/neg/autoTuplingTest.scala
@@ -1,5 +1,3 @@
-import dotty.language.noAutoTupling
-
 object autoTuplingNeg2 {
 
   val x = Some(1, 2) // error: too many arguments for method apply: (x: A)Some[A]
diff --git a/tests/pending/pos/t2913.scala b/tests/pos/t2913.scala
index 21700e71a..fa91e6f41 100644
--- a/tests/pending/pos/t2913.scala
+++ b/tests/pos/t2913.scala
@@ -1,4 +1,3 @@
-import language.noAutoTupling // try with on and off
 
 class A {
   def foo(a: Int) = 0
@@ -10,7 +9,8 @@ class RichA {
   def foo() = 0
 }
 
-object Test {
+object TestNoAutoTupling {
+  import language.noAutoTupling // try with on and off
 
   implicit def AToRichA(a: A): RichA = new RichA
 
@@ -53,3 +53,26 @@ object Main {
     ()
   }
 }
+
+object TestWithAutoTuling {
+
+  implicit def AToRichA(a: A): RichA = new RichA
+
+  val a = new A
+  a.foo()
+  a.foo(1)
+
+  a.foo("")       // Without implicits, a type error regarding invalid argument types is generated at `""`. This is
+                  // the same position as an argument, so the 'second try' typing with an Implicit View is tried,
+                  // and AToRichA(a).foo("") is found.
+                  //
+                  // My reading of the spec "7.3 Views" is that `a.foo` denotes a member of `a`, so the view should
+                  // not be triggered.
+                  //
+                  // But perhaps the implementation was changed to solve See https://lampsvn.epfl.ch/trac/scala/ticket/1756
+
+  a.foo("a", "b") // Without implicits, a type error regarding invalid arity is generated at `foo(<error>"", "")`.
+                  // Typers#tryTypedApply:3274 only checks if the error is as the same position as `foo`, `"a"`, or `"b"`.
+                  // None of these po
+}
+