Merge pull request #1785 from dotty-staging/fix-#1784

Fix #1784: allow to omit types for local implicit vals

5 files changed, 19 insertions, 8 deletions

diff --git a/compiler/src/dotty/tools/dotc/typer/Applications.scala b/compiler/src/dotty/tools/dotc/typer/Applications.scala
index 11121e1f3..a3b4cb311 100644
--- a/compiler/src/dotty/tools/dotc/typer/Applications.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Applications.scala
@@ -992,7 +992,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
             val nestedCtx = ctx.fresh.setExploreTyperState
 
             {
-              implicit val ctx: Context = nestedCtx
+              implicit val ctx = nestedCtx
               isAsSpecificValueType(tp1, constrained(tp2).resultType)
             }
           case _ => // (3b)
diff --git a/compiler/src/dotty/tools/dotc/typer/ErrorReporting.scala b/compiler/src/dotty/tools/dotc/typer/ErrorReporting.scala
index a18c83ff8..a066fc04a 100644
--- a/compiler/src/dotty/tools/dotc/typer/ErrorReporting.scala
+++ b/compiler/src/dotty/tools/dotc/typer/ErrorReporting.scala
@@ -46,7 +46,13 @@ object ErrorReporting {
             errorMsg(msg, cx.outer)
         }
       } else msg
-    errorMsg(ex.show, ctx)
+
+      if (cycleSym.is(Implicit, butNot = Method) && cycleSym.owner.isTerm)
+        em"""cyclic reference involving implicit $cycleSym
+            |This happens when the right hand-side of $cycleSym's definition involves an implicit search.
+            |To avoid the error, give $cycleSym an explicit type."""
+      else
+        errorMsg(ex.show, ctx)
   }
 
   def wrongNumberOfArgs(fntpe: Type, kind: String, expectedArgs: List[TypeParamInfo], actual: List[untpd.Tree], pos: Position)(implicit ctx: Context) =
diff --git a/compiler/src/dotty/tools/dotc/typer/Inliner.scala b/compiler/src/dotty/tools/dotc/typer/Inliner.scala
index 3931fcaf4..09487570d 100644
--- a/compiler/src/dotty/tools/dotc/typer/Inliner.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Inliner.scala
@@ -189,7 +189,7 @@ object Inliner {
         if (!ctx.isAfterTyper) {
           val inlineCtx = ctx
           sym.updateAnnotation(LazyBodyAnnotation { _ =>
-            implicit val ctx: Context = inlineCtx
+            implicit val ctx = inlineCtx
             ctx.withNoError(treeExpr(ctx))(makeInlineable)
           })
         }
diff --git a/compiler/src/dotty/tools/dotc/typer/Namer.scala b/compiler/src/dotty/tools/dotc/typer/Namer.scala
index b8fe46745..4bcdd5071 100644
--- a/compiler/src/dotty/tools/dotc/typer/Namer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Namer.scala
@@ -683,7 +683,7 @@ class Namer { typer: Typer =>
         //println(i"completing type params of $sym in ${sym.owner}")
         nestedCtx = localContext(sym).setNewScope
         myTypeParams = {
-          implicit val ctx: Context = nestedCtx
+          implicit val ctx = nestedCtx
           val tparams = original.rhs match {
             case PolyTypeTree(tparams, _) => tparams
             case _ => Nil
@@ -998,11 +998,16 @@ class Namer { typer: Typer =>
           lhsType // keep constant types that fill in for a non-constant (to be revised when inline has landed).
         else inherited
       else {
-        if (sym is Implicit) {
-          val resStr = if (mdef.isInstanceOf[DefDef]) "result " else ""
-          ctx.error(s"${resStr}type of implicit definition needs to be given explicitly", mdef.pos)
+        def missingType(modifier: String) = {
+          ctx.error(s"${modifier}type of implicit definition needs to be given explicitly", mdef.pos)
           sym.resetFlag(Implicit)
         }
+        if (sym is Implicit)
+          mdef match {
+            case _: DefDef => missingType("result")
+            case _: ValDef if sym.owner.isType => missingType("")
+            case _ =>
+          }
         lhsType orElse WildcardType
       }
     }
diff --git a/compiler/src/dotty/tools/dotc/typer/Typer.scala b/compiler/src/dotty/tools/dotc/typer/Typer.scala
index 78c479433..eec3859f9 100644
--- a/compiler/src/dotty/tools/dotc/typer/Typer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Typer.scala
@@ -1642,7 +1642,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       tryInsertImplicitOnQualifier(tree, pt).getOrElse(fallBack)
 
     if (isApplyProto(pt)) tryImplicit
-    else tryEither(tryApply(_))((_, _) => tryImplicit) 
+    else tryEither(tryApply(_))((_, _) => tryImplicit)
   }
 
   /** If this tree is a select node `qual.name`, try to insert an implicit conversion