SI-4492 More informative error when class not found on classpath

Position the error based on Select tree that failed to type check,
presumably due to an underlying MissingRequirementError, which has no position.

There are lots of other ways we could rewrap a MRE and supplement position info,
but that remains TODO. Jason's review comment is recorded in the code.

Also try to detect the case of a missing module and provide some advice,
as well as linking to the forthcoming 2.11 guide at
http://docs.scala-lang.org/overviews/core/scala-2.11.html.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
index 994a2a4f4f..8e1ceffecd 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Contexts.scala
@@ -103,7 +103,7 @@ trait Contexts { self: Analyzer =>
 
     // there must be a scala.xml package when xml literals were parsed in this unit
     if (unit.hasXml && ScalaXmlPackage == NoSymbol)
-      unit.error(unit.firstXmlPos, "To compile XML syntax, the scala.xml package must be on the classpath.\nPlease see https://github.com/scala/scala/wiki/Scala-2.11#xml.")
+      unit.error(unit.firstXmlPos, "To compile XML syntax, the scala.xml package must be on the classpath.\nPlease see http://docs.scala-lang.org/overviews/core/scala-2.11.html#scala-xml.")
 
     // scala-xml needs `scala.xml.TopScope` to be in scope globally as `$scope`
     // We detect `scala-xml` by looking for `scala.xml.TopScope` and
@@ -544,6 +544,8 @@ trait Contexts { self: Analyzer =>
       if (checking) onTreeCheckerError(pos, msg) else unit.error(pos, msg)
 
     @inline private def issueCommon(err: AbsTypeError)(pf: PartialFunction[AbsTypeError, Unit]) {
+      // TODO: are errors allowed to have pos == NoPosition??
+      // if not, Jason suggests doing: val pos = err.errPos.orElse( { devWarning("Que?"); context.tree.pos })
       if (settings.Yissuedebug) {
         log("issue error: " + err.errMsg)
         (new Exception).printStackTrace()