Merge pull request scala#3631 from adriaanm/t4492

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

Author: adriaanm

src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala

@@ -359,6 +359,14 @@ trait ContextErrors {
         //setError(sel)
       }
 
+      def SelectWithUnderlyingError(sel: Tree, err: AbsTypeError) = {
+        // if there's no position, this is likely the result of a MissingRequirementError
+        // use the position of the selection we failed to type check to report the original message
+        if (err.errPos == NoPosition) issueNormalTypeError(sel, err.errMsg)
+        else issueTypeError(err)
+        setError(sel)
+      }
+
       //typedNew
       def IsAbstractError(tree: Tree, sym: Symbol) = {
         issueNormalTypeError(tree, sym + " is abstract; cannot be instantiated")

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()

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -4670,8 +4670,8 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
             case SilentTypeError(err: AccessTypeError) =>
               (tree1, Some(err))
             case SilentTypeError(err) =>
-              context issue err
-              return setError(tree)
+              SelectWithUnderlyingError(tree, err)
+              return tree
             case SilentResultValue(treeAndPre) =>
               (stabilize(treeAndPre._1, treeAndPre._2, mode, pt), None)
           }

src/reflect/scala/reflect/internal/pickling/UnPickler.scala

@@ -229,6 +229,20 @@ abstract class UnPickler {
           NoSymbol
         }
 
+        def moduleAdvice(missing: String): String = {
+          val module =
+            if      (missing.startsWith("scala.xml"))                Some(("org.scala-lang.modules", "scala-xml"))
+            else if (missing.startsWith("scala.util.parsing"))       Some(("org.scala-lang.modules", "scala-parser-combinators"))
+            else if (missing.startsWith("scala.swing"))              Some(("org.scala-lang.modules", "scala-swing"))
+            else if (missing.startsWith("scala.util.continuations")) Some(("org.scala-lang.plugins", "scala-continuations-library"))
+            else None
+
+          (module map { case (group, art) =>
+            s"""\n(NOTE: It looks like the $art module is missing; try adding a dependency on "$group" : "$art".
+               |       See http://docs.scala-lang.org/overviews/core/scala-2.11.html for more information.)""".stripMargin
+           } getOrElse "")
+        }
+
         // (1) Try name.
         fromName(name) orElse {
           // (2) Try with expanded name.  Can happen if references to private
@@ -240,11 +254,12 @@ abstract class UnPickler {
               // (4) Call the mirror's "missing" hook.
               adjust(mirrorThatLoaded(owner).missingHook(owner, name)) orElse {
                 // (5) Create a stub symbol to defer hard failure a little longer.
+                val fullName = s"${owner.fullName}.$name"
                 val missingMessage =
-                  s"""|bad symbolic reference. A signature in $filename refers to ${name.longString}
-                      |in ${owner.kindString} ${owner.fullName} 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 $filename.""".stripMargin
+                  s"""|bad symbolic reference to $fullName encountered in class file '$filename'.
+                      |Cannot access ${name.longString} in ${owner.kindString} ${owner.fullName}. The current classpath may be
+                      |missing a definition for $fullName, or $filename may have been compiled against a version that's
+                      |incompatible with the one found on the current classpath.${moduleAdvice(fullName)}""".stripMargin
                 owner.newStubSymbol(name, missingMessage)
               }
             }

test/files/neg/t5148.check

@@ -1,5 +1,5 @@
-error: bad symbolic reference. A signature in Imports.class refers to type Request
-in class scala.tools.nsc.interpreter.IMain 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 Imports.class.
+error: bad symbolic reference to scala.tools.nsc.interpreter.IMain.Request encountered in class file 'Imports.class'.
+Cannot access type Request in class scala.tools.nsc.interpreter.IMain. The current classpath may be
+missing a definition for scala.tools.nsc.interpreter.IMain.Request, or Imports.class may have been compiled against a version that's
+incompatible with the one found on the current classpath.
 one error found

test/files/run/t6440.check

@@ -1,4 +1,4 @@
-pos: source-newSource1.scala,line-9,offset=109 bad symbolic reference. A signature in U.class refers to term pack1
-in package <root> 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 U.class. ERROR
+pos: source-newSource1.scala,line-9,offset=109 bad symbolic reference to <root>.pack1 encountered in class file 'U.class'.
+Cannot access term pack1 in package <root>. The current classpath may be
+missing a definition for <root>.pack1, or U.class may have been compiled against a version that's
+incompatible with the one found on the current classpath. ERROR

test/files/run/t6440b.check

@@ -1,4 +1,4 @@
-pos: NoPosition bad symbolic reference. A signature in U.class refers to type T
-in package pack1 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 U.class. ERROR
+pos: NoPosition bad symbolic reference to pack1.T encountered in class file 'U.class'.
+Cannot access type T in package pack1. The current classpath may be
+missing a definition for pack1.T, or U.class may have been compiled against a version that's
+incompatible with the one found on the current classpath. ERROR