Handle import aliases of implicit definitions

This makes scala#2405 work again.

Author: odersky

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

@@ -201,7 +201,7 @@ object Contexts {
     def implicits: ContextualImplicits = {
       if (implicitsCache == null )
         implicitsCache = {
-          val implicitRefs: List[TermRef] =
+          val implicitRefs: List[ImplicitDef] =
             if (isClassDefContext)
               try owner.thisType.implicitMembers
               catch {

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

@@ -1969,7 +1969,16 @@ object Types {
     override def eql(that: Type) = this eq that // safe because named types are hash-consed separately
   }
 
-  abstract case class TermRef(override val prefix: Type, var designator: Designator) extends NamedType with SingletonType {
+  /** A reference to an implicit definition. This can be either a TermRef or a
+   *  Implicits.RenamedImplicitDef.
+   */
+  trait ImplicitDef {
+    def implicitName(implicit ctx: Context): TermName
+    def implicitRef: TermRef
+  }
+
+  abstract case class TermRef(override val prefix: Type, var designator: Designator)
+  extends NamedType with SingletonType with ImplicitDef {
 
     type ThisType = TermRef
     type ThisName = TermName
@@ -1987,6 +1996,9 @@ object Types {
 
     def altsWith(p: Symbol => Boolean)(implicit ctx: Context): List[TermRef] =
       denot.altsWith(p).map(withDenot(_))
+
+    def implicitName(implicit ctx: Context): TermName = name
+    def implicitRef = this
   }
 
   abstract case class TypeRef(override val prefix: Type, var designator: Designator) extends NamedType {

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

@@ -45,11 +45,20 @@ object Implicits {
    */
   val DelayedImplicit = new Property.Key[TermRef]
 
+  /** An implicit definition `implicitRef` that is visible under a different name, `alias`.
+   *  Gets generated if an implicit ref is imported via a renaming import.
+   */
+  class RenamedImplicitDef(val implicitRef: TermRef, val alias: TermName) extends ImplicitDef {
+    def implicitName(implicit ctx: Context): TermName = alias
+  }
+
   /** An eligible implicit candidate, consisting of an implicit reference and a nesting level */
-  case class Candidate(ref: TermRef, level: Int)
+  case class Candidate(implicitDef: ImplicitDef, level: Int) {
+    def ref: TermRef = implicitDef.implicitRef
+  }
 
   /** A common base class of contextual implicits and of-type implicits which
-   *  represents a set of implicit references.
+   *  represents a set of references to implicit definitions.
    */
   abstract class ImplicitRefs(initctx: Context) {
     implicit val ctx: Context =
@@ -59,7 +68,7 @@ object Implicits {
     def level: Int = 0
 
     /** The implicit references */
-    def refs: List[TermRef]
+    def refs: List[ImplicitDef]
 
     /** Return those references in `refs` that are compatible with type `pt`. */
     protected def filterMatching(pt: Type)(implicit ctx: Context): List[Candidate] = track("filterMatching") {
@@ -138,7 +147,7 @@ object Implicits {
       else {
         val nestedCtx = ctx.fresh.addMode(Mode.TypevarsMissContext)
         refs
-          .filter(ref => nestedCtx.typerState.test(refMatches(ref)(nestedCtx)))
+          .filter(ref => nestedCtx.typerState.test(refMatches(ref.implicitRef)(nestedCtx)))
           .map(Candidate(_, level))
       }
     }
@@ -150,7 +159,7 @@ object Implicits {
    */
   class OfTypeImplicits(tp: Type, val companionRefs: TermRefSet)(initctx: Context) extends ImplicitRefs(initctx) {
     assert(initctx.typer != null)
-    lazy val refs: List[TermRef] = {
+    lazy val refs: List[ImplicitDef] = {
       val buf = new mutable.ListBuffer[TermRef]
       for (companion <- companionRefs) buf ++= companion.implicitMembers
       buf.toList
@@ -176,7 +185,7 @@ object Implicits {
    *                   name, b, whereas the name of the symbol is the original name, a.
    *  @param outerCtx  the next outer context that makes visible further implicits
    */
-  class ContextualImplicits(val refs: List[TermRef], val outerImplicits: ContextualImplicits)(initctx: Context) extends ImplicitRefs(initctx) {
+  class ContextualImplicits(val refs: List[ImplicitDef], val outerImplicits: ContextualImplicits)(initctx: Context) extends ImplicitRefs(initctx) {
     private val eligibleCache = new mutable.AnyRefMap[Type, List[Candidate]]
 
     /** The level increases if current context has a different owner or scope than
@@ -188,7 +197,7 @@ object Implicits {
       else if (ctx.scala2Mode ||
                (ctx.owner eq outerImplicits.ctx.owner) &&
                (ctx.scope eq outerImplicits.ctx.scope) &&
-               !refs.head.name.is(LazyImplicitName)) outerImplicits.level
+               !refs.head.implicitName.is(LazyImplicitName)) outerImplicits.level
       else outerImplicits.level + 1
 
     /** Is this the outermost implicits? This is the case if it either the implicits
@@ -231,8 +240,8 @@ object Implicits {
       val ownEligible = filterMatching(tp)
       if (isOuterMost) ownEligible
       else ownEligible ::: {
-        val shadowed = ownEligible.map(_.ref.name).toSet
-        outerImplicits.eligible(tp).filterNot(cand => shadowed.contains(cand.ref.name))
+        val shadowed = ownEligible.map(_.ref.implicitName).toSet
+        outerImplicits.eligible(tp).filterNot(cand => shadowed.contains(cand.ref.implicitName))
       }
     }
 
@@ -818,7 +827,7 @@ trait Implicits { self: Typer =>
             pt)
         val generated1 = adapt(generated, pt)
         lazy val shadowing =
-          typed(untpd.Ident(ref.name) withPos pos.toSynthetic, funProto)(
+          typed(untpd.Ident(cand.implicitDef.implicitName) withPos pos.toSynthetic, funProto)(
             nestedContext().addMode(Mode.ImplicitShadowing).setExploreTyperState())
         def refSameAs(shadowing: Tree): Boolean =
           ref.symbol == closureBody(shadowing).symbol || {

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

@@ -9,6 +9,7 @@ import printing.{Printer, Showable}
 import util.SimpleIdentityMap
 import Symbols._, Names._, Denotations._, Types._, Contexts._, StdNames._, Flags._
 import Decorators.StringInterpolators
+import Implicits.RenamedImplicitDef
 
 object ImportInfo {
   /** The import info for a root import from given symbol `sym` */
@@ -92,7 +93,7 @@ class ImportInfo(symf: Context => Symbol, val selectors: List[untpd.Tree],
   }
 
   /** The implicit references imported by this import clause */
-  def importedImplicits(implicit ctx: Context): List[TermRef] = {
+  def importedImplicits(implicit ctx: Context): List[ImplicitDef] = {
     val pre = site
     if (isWildcardImport) {
       val refs = pre.implicitMembers
@@ -102,7 +103,12 @@ class ImportInfo(symf: Context => Symbol, val selectors: List[untpd.Tree],
       for {
         renamed <- reverseMapping.keys
         denot <- pre.member(reverseMapping(renamed)).altsWith(_ is Implicit)
-      } yield TermRef(pre, renamed, denot)
+      } yield {
+        val original = reverseMapping(renamed)
+        val ref = TermRef(pre, original, denot)
+        if (renamed == original) ref
+        else new RenamedImplicitDef(ref, renamed)
+      }
   }
 
   /** The root import symbol hidden by this symbol, or NoSymbol if no such symbol is hidden.

tests/pos/t2405.scala

@@ -0,0 +1,23 @@
+object A { implicit val x: Int = 1 }
+
+// Problem as stated in the ticket.
+object Test1 {
+    import A.{x => y}
+    implicitly[Int]
+}
+
+// Testing for the absense of shadowing #1.
+object Test2 {
+    import A.{x => y}
+    val x = 2
+    implicitly[Int]
+}
+
+// Testing for the absense of shadowing #2.
+object Test3 {
+    {
+        import A.{x => y}
+        def x: Int = 0
+        implicitly[Int]
+    }
+}