Fix #3540: Added suggestions from code review.

Author: vitorsvieira

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

@@ -18,6 +18,8 @@ import util.Stats
 import java.util.WeakHashMap
 import config.Config
 import config.Printers.{incremental, noPrinter}
+import reporting.diagnostic.Message
+import reporting.diagnostic.messages.BadSymbolicReference
 import reporting.trace
 
 trait SymDenotations { this: Context =>
@@ -1956,7 +1958,7 @@ object SymDenotations {
   /** A completer for missing references */
   class StubInfo() extends LazyType {
 
-    def initializeToDefaults(denot: SymDenotation, errMsg: => String)(implicit ctx: Context) = {
+    def initializeToDefaults(denot: SymDenotation, errMsg: => Message)(implicit ctx: Context): Unit = {
       denot.info = denot match {
         case denot: ClassDenotation =>
           ClassInfo(denot.owner.thisType, denot.classSymbol, Nil, EmptyScope)
@@ -1968,18 +1970,9 @@ object SymDenotations {
 
     def complete(denot: SymDenotation)(implicit ctx: Context): Unit = {
       val sym = denot.symbol
-      val file = sym.associatedFile
-      val (location, src) =
-        if (file != null) (s" in $file", file.toString)
-        else ("", "the signature")
-      val name = ctx.fresh.setSetting(ctx.settings.YdebugNames, true).nameString(denot.name)
-      def errMsg =
-        i"""bad symbolic reference. A signature$location
-           |refers to $name in ${denot.owner.showKind} ${denot.owner.showFullName} which is not available.
-           |It may be completely missing from the current classpath, or the version on
-           |the classpath might be incompatible with the version used when compiling $src."""
-      ctx.error(errMsg)
-      if (ctx.debug) throw new Error()
+      def errMsg = BadSymbolicReference(denot)
+      ctx.error(errMsg, sym.pos)
+      if (ctx.debug) throw new scala.Error()
       initializeToDefaults(denot, errMsg)
     }
   }

compiler/src/dotty/tools/dotc/reporting/diagnostic/ErrorMessageID.java

@@ -118,6 +118,7 @@ public enum ErrorMessageID {
     UnapplyInvalidNumberOfArgumentsID,
     StaticFieldsOnlyAllowedInObjectsID,
     CyclicInheritanceID,
+    BadSymbolicReferenceID,
     UnableToExtendSealedClassID,
     SymbolHasUnparsableVersionNumberID,
     SymbolChangedSemanticsInVersionID,

compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala

@@ -1978,6 +1978,26 @@ object messages {
     }
   }
 
+  case class BadSymbolicReference(denot: SymDenotation)(implicit ctx: Context) extends Message(BadSymbolicReferenceID) {
+    val kind = "Reference"
+
+    val msg = {
+      val denotationOwner = denot.owner
+      val denotationName = ctx.fresh.setSetting(ctx.settings.YdebugNames, true).nameString(denot.name)
+      val file = denot.symbol.associatedFile
+      val (location, src) =
+        if (file != null) (s" in $file", file.toString)
+        else ("", "the signature")
+
+      hl"""Bad symbolic reference. A signature$location
+          |refers to $denotationName in ${denotationOwner.showKind} ${denotationOwner.showFullName} which is not available.
+          |It may be completely missing from the current classpath, or the version on
+          |the classpath might be incompatible with the version used when compiling $src."""
+    }
+
+    val explanation = ""
+  }
+
   case class UnableToExtendSealedClass(pclazz: Symbol)(implicit ctx: Context) extends Message(UnableToExtendSealedClassID) {
     val kind = "Syntax"
     val msg = hl"Cannot extend ${"sealed"} $pclazz in a different source file"

tests/pos/i3540.scala

@@ -1,5 +1,5 @@
 object Test {
   implicit class Foo(x: Int)(implicit y: Int)
-  implicit class Foo(x: Int)(y: Int)(implicit z: Int) // OK but not used during implicit lookup
-  implicit class Foo(x: Int)(y: Int)                  // OK but not used during implicit lookup
+  implicit class Foo0(x: Int)(y: Int)(implicit z: Int) // OK but not used during implicit lookup
+  implicit class Foo1(x: Int)(y: Int)                  // OK but not used during implicit lookup
 }