Refine import implied rules to smooth migration

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -396,7 +396,7 @@ object desugar {
         if (enumCases.isEmpty)
           ctx.error("Enumerations must constain at least one case", namePos)
         val enumCompanionRef = new TermRefTree()
-        val enumImport = Import(impliedOnly = false, enumCompanionRef, enumCases.flatMap(caseIds))
+        val enumImport = Import(importImplied = false, enumCompanionRef, enumCases.flatMap(caseIds))
         (enumImport :: enumStats, enumCases, enumCompanionRef)
       }
       else (stats, Nil, EmptyTree)

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -751,7 +751,7 @@ object Trees {
    *  where a selector is either an untyped `Ident`, `name` or
    *  an untyped thicket consisting of `name` and `rename`.
    */
-  case class Import[-T >: Untyped] private[ast] (impliedOnly: Boolean, expr: Tree[T], selectors: List[Tree[Untyped]])(implicit @constructorOnly src: SourceFile)
+  case class Import[-T >: Untyped] private[ast] (importImplied: Boolean, expr: Tree[T], selectors: List[Tree[Untyped]])(implicit @constructorOnly src: SourceFile)
     extends DenotingTree[T] {
     type ThisTree[-T >: Untyped] = Import[T]
   }
@@ -1140,9 +1140,9 @@ object Trees {
         case tree: Template if (constr eq tree.constr) && (parents eq tree.parents) && (derived eq tree.derived) && (self eq tree.self) && (body eq tree.unforcedBody) => tree
         case tree => finalize(tree, untpd.Template(constr, parents, derived, self, body)(sourceFile(tree)))
       }
-      def Import(tree: Tree)(impliedOnly: Boolean, expr: Tree, selectors: List[untpd.Tree])(implicit ctx: Context): Import = tree match {
-        case tree: Import if (impliedOnly == tree.impliedOnly) && (expr eq tree.expr) && (selectors eq tree.selectors) => tree
-        case _ => finalize(tree, untpd.Import(impliedOnly, expr, selectors)(sourceFile(tree)))
+      def Import(tree: Tree)(importImplied: Boolean, expr: Tree, selectors: List[untpd.Tree])(implicit ctx: Context): Import = tree match {
+        case tree: Import if (importImplied == tree.importImplied) && (expr eq tree.expr) && (selectors eq tree.selectors) => tree
+        case _ => finalize(tree, untpd.Import(importImplied, expr, selectors)(sourceFile(tree)))
       }
       def PackageDef(tree: Tree)(pid: RefTree, stats: List[Tree])(implicit ctx: Context): PackageDef = tree match {
         case tree: PackageDef if (pid eq tree.pid) && (stats eq tree.stats) => tree
@@ -1283,8 +1283,8 @@ object Trees {
               cpy.TypeDef(tree)(name, transform(rhs))
             case tree @ Template(constr, parents, self, _) if tree.derived.isEmpty =>
               cpy.Template(tree)(transformSub(constr), transform(tree.parents), Nil, transformSub(self), transformStats(tree.body))
-            case Import(impliedOnly, expr, selectors) =>
-              cpy.Import(tree)(impliedOnly, transform(expr), selectors)
+            case Import(importImplied, expr, selectors) =>
+              cpy.Import(tree)(importImplied, transform(expr), selectors)
             case PackageDef(pid, stats) =>
               cpy.PackageDef(tree)(transformSub(pid), transformStats(stats)(localCtx))
             case Annotated(arg, annot) =>
@@ -1403,7 +1403,7 @@ object Trees {
               this(x, rhs)
             case tree @ Template(constr, parents, self, _) if tree.derived.isEmpty =>
               this(this(this(this(x, constr), parents), self), tree.body)
-            case Import(impliedOnly, expr, selectors) =>
+            case Import(importImplied, expr, selectors) =>
               this(x, expr)
             case PackageDef(pid, stats) =>
               this(this(x, pid), stats)(localCtx)

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -326,8 +326,8 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
     Block(cdef :: Nil, New(cls.typeRef, Nil))
   }
 
-  def Import(impliedOnly: Boolean, expr: Tree, selectors: List[untpd.Tree])(implicit ctx: Context): Import =
-    ta.assignType(untpd.Import(impliedOnly, expr, selectors), ctx.newImportSymbol(ctx.owner, expr))
+  def Import(importImplied: Boolean, expr: Tree, selectors: List[untpd.Tree])(implicit ctx: Context): Import =
+    ta.assignType(untpd.Import(importImplied, expr, selectors), ctx.newImportSymbol(ctx.owner, expr))
 
   def PackageDef(pid: RefTree, stats: List[Tree])(implicit ctx: Context): PackageDef =
     ta.assignType(untpd.PackageDef(pid, stats), pid)

compiler/src/dotty/tools/dotc/ast/untpd.scala

@@ -323,7 +323,7 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
   def Template(constr: DefDef, parents: List[Tree], derived: List[Tree], self: ValDef, body: LazyTreeList)(implicit src: SourceFile): Template =
     if (derived.isEmpty) new Template(constr, parents, self, body)
     else new DerivingTemplate(constr, parents ++ derived, self, body, derived.length)
-  def Import(impliedOnly: Boolean, expr: Tree, selectors: List[Tree])(implicit src: SourceFile): Import = new Import(impliedOnly, expr, selectors)
+  def Import(importImplied: Boolean, expr: Tree, selectors: List[Tree])(implicit src: SourceFile): Import = new Import(importImplied, expr, selectors)
   def PackageDef(pid: RefTree, stats: List[Tree])(implicit src: SourceFile): PackageDef = new PackageDef(pid, stats)
   def Annotated(arg: Tree, annot: Tree)(implicit src: SourceFile): Annotated = new Annotated(arg, annot)
 

compiler/src/dotty/tools/dotc/core/ConstraintHandling.scala

@@ -85,7 +85,8 @@ trait ConstraintHandling[AbstractContext] {
 
       val oldBounds @ TypeBounds(lo, hi) = constraint.nonParamBounds(param)
       val equalBounds = isUpper && (lo eq bound) || !isUpper && (bound eq hi)
-      if (equalBounds && !bound.existsPart(_.isInstanceOf[WildcardType])) {
+      if (equalBounds &&
+         !bound.existsPart(bp => bp.isInstanceOf[WildcardType] || (bp eq param))) {
         // The narrowed bounds are equal and do not contain wildcards,
         // so we can remove `param` from the constraint.
         // (Handling wildcards requires choosing a bound, but we don't know which

compiler/src/dotty/tools/dotc/core/Contexts.scala

@@ -151,13 +151,11 @@ object Contexts {
     /** The current type comparer. This ones updates itself automatically for
      *  each new context.
      */
-    private[this] var _typeComparer: TypeComparer = null
-    protected def typeComparer_=(typeComparer: TypeComparer): Unit = {
-      assert(typeComparer.ctx eq this)
-      _typeComparer = typeComparer
-    }
-    final def typeComparer: TypeComparer = {
-      if (_typeComparer == null) _typeComparer = outer.typeComparer.copyIn(this)
+    private[this] var _typeComparer: TypeComparer = _
+    protected def typeComparer_=(typeComparer: TypeComparer): Unit = _typeComparer = typeComparer
+    def typeComparer: TypeComparer = {
+      if (_typeComparer.ctx ne this)
+        _typeComparer = _typeComparer.copyIn(this)
       _typeComparer
     }
 
@@ -406,7 +404,7 @@ object Contexts {
         case _               => None
       }
       ctx.fresh.setImportInfo(
-        new ImportInfo(implicit ctx => sym, imp.selectors, impNameOpt, imp.impliedOnly))
+        new ImportInfo(implicit ctx => sym, imp.selectors, impNameOpt, imp.importImplied))
     }
 
     /** Does current phase use an erased types interpretation? */
@@ -422,29 +420,31 @@ object Contexts {
     def useColors: Boolean =
       base.settings.color.value == "always"
 
-    protected def init(outer: Context): this.type = {
+    protected def init(outer: Context, origin: Context): this.type = {
+      util.Stats.record("Context.fresh")
       _outer = outer
-      _period = outer.period
-      _mode = outer.mode
-      _owner = outer.owner
-      _tree = outer.tree
-      _scope = outer.scope
-      _typerState = outer.typerState
-      _typeAssigner = outer.typeAssigner
-      _importInfo = outer.importInfo
-      _gadt = outer.gadt
-      _searchHistory = outer.searchHistory
-      _source = outer.source
-      _moreProperties = outer.moreProperties
-      _store = outer.store
+      _period = origin.period
+      _mode = origin.mode
+      _owner = origin.owner
+      _tree = origin.tree
+      _scope = origin.scope
+      _typerState = origin.typerState
+      _typeAssigner = origin.typeAssigner
+      _importInfo = origin.importInfo
+      _gadt = origin.gadt
+      _searchHistory = origin.searchHistory
+      _typeComparer = origin.typeComparer
+      _source = origin.source
+      _moreProperties = origin.moreProperties
+      _store = origin.store
       this
     }
 
-    /** A fresh clone of this context. */
-    def fresh: FreshContext = {
-      util.Stats.record("Context.fresh")
-      new FreshContext(base).init(this)
-    }
+    /** A fresh clone of this context embedded in this context. */
+    def fresh: FreshContext = freshOver(this)
+
+    /** A fresh clone of this context embedded in the specified `outer` context. */
+    def freshOver(outer: Context): FreshContext = new FreshContext(base).init(outer, this)
 
     final def withOwner(owner: Symbol): Context =
       if (owner ne this.owner) fresh.setOwner(owner) else this

compiler/src/dotty/tools/dotc/core/Mode.scala

@@ -101,4 +101,7 @@ object Mode {
 
   /** We are synthesizing the receiver of an extension method */
   val SynthesizeExtMethodReceiver: Mode = newMode(23, "SynthesizeExtMethodReceiver")
+
+  /** Are we trying to find a hidden implicit? */
+  val FindHiddenImplicits: Mode = newMode(24, "FindHiddenImplicits")
 }

compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala

@@ -532,10 +532,10 @@ class TreePickler(pickler: TastyPickler) {
             }
             pickleStats(tree.constr :: rest)
           }
-        case Import(impliedOnly, expr, selectors) =>
+        case Import(importImplied, expr, selectors) =>
           writeByte(IMPORT)
           withLength {
-            if (impliedOnly) writeByte(IMPLIED)
+            if (importImplied) writeByte(IMPLIED)
             pickleTree(expr)
             pickleSelectors(selectors)
           }

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -954,10 +954,10 @@ class TreeUnpickler(reader: TastyReader,
       assert(sourcePathAt(start).isEmpty)
       readByte()
       readEnd()
-      val impliedOnly = nextByte == IMPLIED
-      if (impliedOnly) readByte()
+      val importImplied = nextByte == IMPLIED
+      if (importImplied) readByte()
       val expr = readTerm()
-      setSpan(start, Import(impliedOnly, expr, readSelectors()))
+      setSpan(start, Import(importImplied, expr, readSelectors()))
     }
 
     def readSelectors()(implicit ctx: Context): List[untpd.Tree] = nextByte match {

compiler/src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -1049,7 +1049,7 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
           val to = untpd.Ident(toName)
           if (toName.isEmpty) from else untpd.Thicket(from, untpd.Ident(toName))
         })
-        Import(impliedOnly = false, expr, selectors)
+        Import(importImplied = false, expr, selectors)
 
       case TEMPLATEtree =>
         setSym()

compiler/src/dotty/tools/dotc/parsing/JavaParsers.scala

@@ -600,7 +600,7 @@ object JavaParsers {
       }
 
     def importCompanionObject(cdef: TypeDef): Tree =
-      Import(impliedOnly = false, Ident(cdef.name.toTermName).withSpan(NoSpan), Ident(nme.WILDCARD) :: Nil)
+      Import(importImplied = false, Ident(cdef.name.toTermName).withSpan(NoSpan), Ident(nme.WILDCARD) :: Nil)
 
     // Importing the companion object members cannot be done uncritically: see
     // ticket #2377 wherein a class contains two static inner classes, each of which
@@ -662,7 +662,7 @@ object JavaParsers {
 //          case nme.WILDCARD => Pair(ident, Ident(null) withPos Span(-1))
 //          case _            => Pair(ident, ident)
 //        }
-        val imp = atSpan(start) { Import(impliedOnly = false, qual, List(ident)) }
+        val imp = atSpan(start) { Import(importImplied = false, qual, List(ident)) }
         imp :: Nil
       }
     }

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2222,9 +2222,9 @@ object Parsers {
      */
     def importClause(): List[Tree] = {
       val offset = accept(IMPORT)
-      val impliedOnly = in.token == IMPLIED
-      if (impliedOnly) in.nextToken()
-      commaSeparated(importExpr(impliedOnly)) match {
+      val importImplied = in.token == IMPLIED
+      if (importImplied) in.nextToken()
+      commaSeparated(importExpr(importImplied)) match {
         case t :: rest =>
           // The first import should start at the start offset of the keyword.
           val firstPos =
@@ -2237,11 +2237,11 @@ object Parsers {
 
     /**  ImportExpr ::= StableId `.' (id | `_' | ImportSelectors)
      */
-    def importExpr(impliedOnly: Boolean): () => Import = {
+    def importExpr(importImplied: Boolean): () => Import = {
 
       val handleImport: Tree => Tree = { tree: Tree =>
-        if (in.token == USCORE) Import(impliedOnly, tree, importSelector() :: Nil)
-        else if (in.token == LBRACE) Import(impliedOnly, tree, inBraces(importSelectors()))
+        if (in.token == USCORE) Import(importImplied, tree, importSelector() :: Nil)
+        else if (in.token == LBRACE) Import(importImplied, tree, inBraces(importSelectors()))
         else tree
       }
 
@@ -2250,10 +2250,10 @@ object Parsers {
           imp
         case sel @ Select(qual, name) =>
           val selector = atSpan(pointOffset(sel)) { Ident(name) }
-          cpy.Import(sel)(impliedOnly, qual, selector :: Nil)
+          cpy.Import(sel)(importImplied, qual, selector :: Nil)
         case t =>
           accept(DOT)
-          Import(impliedOnly, t, Ident(nme.WILDCARD) :: Nil)
+          Import(importImplied, t, Ident(nme.WILDCARD) :: Nil)
       }
     }
 

compiler/src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -487,7 +487,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
             typeDefText(tparamsTxt, optText(rhs)(" = " ~ _))
         }
         recur(rhs, "")
-      case Import(impliedOnly, expr, selectors) =>
+      case Import(importImplied, expr, selectors) =>
         def selectorText(sel: Tree): Text = sel match {
           case Thicket(l :: r :: Nil) => toTextGlobal(l) ~ " => " ~ toTextGlobal(r)
           case _ => toTextGlobal(sel)
@@ -496,7 +496,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
           case id :: Nil => toText(id)
           case _ => "{" ~ Text(selectors map selectorText, ", ") ~ "}"
         }
-        keywordText("import ") ~ (keywordText("implied ") provided impliedOnly) ~
+        keywordText("import ") ~ (keywordText("implied ") provided importImplied) ~
         toTextLocal(expr) ~ "." ~ selectorsText
       case packageDef: PackageDef =>
         packageDefText(packageDef)

compiler/src/dotty/tools/dotc/sbt/ExtractDependencies.scala

@@ -339,10 +339,10 @@ private class ExtractDependenciesCollector extends tpd.TreeTraverser { thisTreeT
     tree match {
       case Match(selector, _) =>
         addPatMatDependency(selector.tpe)
-      case Import(impliedOnly, expr, selectors) =>
+      case Import(importImplied, expr, selectors) =>
         def lookupImported(name: Name) = {
           val sym = expr.tpe.member(name).symbol
-          if (sym.is(Implied) == impliedOnly) sym else NoSymbol
+          if (sym.is(Implied) == importImplied) sym else NoSymbol
         }
         def addImported(name: Name) = {
           // importing a name means importing both a term and a type (if they exist)

compiler/src/dotty/tools/dotc/tastyreflect/KernelImpl.scala

@@ -86,15 +86,15 @@ class KernelImpl(val rootContext: core.Contexts.Context, val rootPosition: util.
     case _ => None
   }
 
-  def Import_impliedOnly(self: Import): Boolean = self.impliedOnly
+  def Import_implied(self: Import): Boolean = self.importImplied
   def Import_expr(self: Import)(implicit ctx: Context): Tree = self.expr
   def Import_selectors(self: Import)(implicit ctx: Context): List[ImportSelector] = self.selectors
 
-  def Import_apply(impliedOnly: Boolean, expr: Term, selectors: List[ImportSelector])(implicit ctx: Context): Import =
-    withDefaultPos(ctx => tpd.Import(impliedOnly, expr, selectors)(ctx))
+  def Import_apply(importImplied: Boolean, expr: Term, selectors: List[ImportSelector])(implicit ctx: Context): Import =
+    withDefaultPos(ctx => tpd.Import(importImplied, expr, selectors)(ctx))
 
-  def Import_copy(original: Import)(impliedOnly: Boolean, expr: Term, selectors: List[ImportSelector])(implicit ctx: Context): Import =
-    tpd.cpy.Import(original)(impliedOnly, expr, selectors)
+  def Import_copy(original: Import)(importImplied: Boolean, expr: Term, selectors: List[ImportSelector])(implicit ctx: Context): Import =
+    tpd.cpy.Import(original)(importImplied, expr, selectors)
 
   type Definition = tpd.Tree
 

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -998,7 +998,7 @@ trait Checking {
         val cases =
           for (stat <- impl.body if isCase(stat))
           yield untpd.Ident(stat.symbol.name.toTermName)
-        val caseImport: Import = Import(impliedOnly = false, ref(cdef.symbol), cases)
+        val caseImport: Import = Import(importImplied = false, ref(cdef.symbol), cases)
         val caseCtx = enumCtx.importContext(caseImport, caseImport.symbol)
         for (stat <- impl.body) checkCaseOrDefault(stat, caseCtx)
       case _ =>

compiler/src/dotty/tools/dotc/typer/Implicits.scala

@@ -364,7 +364,7 @@ object Implicits {
 
   abstract class SearchFailureType extends ErrorType {
     def expectedType: Type
-    protected def argument: Tree
+    def argument: Tree
 
     /** A "massaging" function for displayed types to give better info in error diagnostics */
     def clarify(tp: Type)(implicit ctx: Context): Type = tp
@@ -822,6 +822,7 @@ trait Implicits { self: Typer =>
   }
 
   def missingArgMsg(arg: Tree, pt: Type, where: String)(implicit ctx: Context): String = {
+
     def msg(shortForm: String)(headline: String = shortForm) = arg match {
       case arg: Trees.SearchFailureIdent[_] =>
         shortForm
@@ -836,6 +837,7 @@ trait Implicits { self: Typer =>
               |But ${tpe.explanation}."""
         }
     }
+
     def location(preposition: String) = if (where.isEmpty) "" else s" $preposition $where"
 
     /** Extract a user defined error message from a symbol `sym`
@@ -898,7 +900,30 @@ trait Implicits { self: Typer =>
             raw,
             pt.typeSymbol.typeParams.map(_.name.unexpandedName.toString),
             pt.argInfos))
-        msg(userDefined.getOrElse(em"no implicit argument of type $pt was found${location("for")}"))()
+
+        def hiddenImplicitsAddendum: String = arg.tpe match {
+          case fail: SearchFailureType =>
+
+            def hiddenImplicitNote(s: SearchSuccess) =
+              em"\n\nNote: implied instance ${s.ref.symbol.showLocated} was not considered because it was not imported with an `import implied`."
+
+            def FindHiddenImplicitsCtx(ctx: Context): Context =
+              if (ctx == NoContext) ctx
+              else ctx.freshOver(FindHiddenImplicitsCtx(ctx.outer)).addMode(Mode.FindHiddenImplicits)
+
+            inferImplicit(fail.expectedType, fail.argument, arg.span)(
+              FindHiddenImplicitsCtx(ctx)) match {
+              case s: SearchSuccess => hiddenImplicitNote(s)
+              case f: SearchFailure =>
+                f.reason match {
+                  case ambi: AmbiguousImplicits => hiddenImplicitNote(ambi.alt1)
+                  case r => ""
+                }
+            }
+        }
+        msg(userDefined.getOrElse(
+          em"no implicit argument of type $pt was found${location("for")}"))() ++
+        hiddenImplicitsAddendum
     }
   }