prohibit case-to-case inheritance instead of issuing warning. closes #4109. review by extempore, since it should make your life much easier in the pattern matcher

git-svn-id: http://lampsvn.epfl.ch/svn-repos/scala/scala/trunk@25282 5e8d7ff9-d8ef-0310-90f0-a4852d11357a

Author: plocinic

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

@@ -34,22 +34,6 @@ trait SyntheticMethods extends ast.TreeDSL {
 
   import global._                  // the global environment
   import definitions._             // standard classes and methods
-  
-  /** In general case classes/objects are not given synthetic equals methods if some
-   *  non-AnyRef implementation is inherited.  However if you let a case object inherit
-   *  an implementation from a case class, it creates an asymmetric equals with all the
-   *  associated badness: see ticket #883.  So if it sees such a thing this has happened
-   *  (by virtue of the symbol being in createdMethodSymbols) it re-overrides it with
-   *  reference equality.
-   *
-   *  TODO: remove once (deprecated) case class inheritance is dropped form nsc.
-   */  
-  private val createdMethodSymbols = new mutable.HashSet[Symbol]
-
-  /** Clear the cache of createdMethodSymbols.  */
-  def resetSynthetics() {
-    createdMethodSymbols.clear()
-  }
 
   /** Add the synthetic methods to case classes.  Note that a lot of the
    *  complexity herein is a consequence of case classes inheriting from
@@ -64,7 +48,7 @@ trait SyntheticMethods extends ast.TreeDSL {
     def hasOverridingImplementation(meth: Symbol): Boolean = {
       val sym = clazz.info nonPrivateMember meth.name
       def isOverride(s: Symbol) = {
-        s != meth && !s.isDeferred && !s.isSynthetic && !createdMethodSymbols(s) &&
+        s != meth && !s.isDeferred && !s.isSynthetic &&
         (clazz.thisType.memberType(s) matches clazz.thisType.memberType(meth))
       }
       sym.alternatives exists isOverride
@@ -75,7 +59,6 @@ trait SyntheticMethods extends ast.TreeDSL {
 
     def newSyntheticMethod(name: Name, flags: Int, tpeCons: Symbol => Type) = {
       val method = clazz.newMethod(clazz.pos.focus, name.toTermName) setFlag flags
-      createdMethodSymbols += method
       method setInfo tpeCons(method)
       clazz.info.decls.enter(method)
     }
@@ -286,13 +269,6 @@ trait SyntheticMethods extends ast.TreeDSL {
           )
         }
 
-        if (clazz.isModuleClass) {
-          // if there's a synthetic method in a parent case class, override its equality
-          // with eq (see #883)
-          val otherEquals = clazz.info.nonPrivateMember(Object_equals.name) 
-          if (otherEquals.owner != clazz && createdMethodSymbols(otherEquals)) ts += equalsModuleMethod
-        }
-
         val methods = (if (clazz.isModuleClass) objectMethods else classMethods) ++ everywhereMethods
         for ((m, impl) <- methods ; if !hasOverridingImplementation(m))
           ts += impl()

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

@@ -50,7 +50,6 @@ trait Typers extends Modes {
     resetNamer()
     resetImplicits()
     transformed.clear()
-    resetSynthetics()
   }
 
   object UnTyper extends Traverser {
@@ -1076,10 +1075,9 @@ trait Typers extends Modes {
     private def validateNoCaseAncestor(clazz: Symbol) = {
       if (!phase.erasedTypes) {
         for (ancestor <- clazz.ancestors find (_.isCase)) {
-          unit.deprecationWarning(clazz.pos, ( 
-            "case class `%s' has case ancestor `%s'.  Case-to-case inheritance has potentially "+
-            "dangerous bugs which are unlikely to be fixed.  You are strongly encouraged to "+
-            "instead use extractors to pattern match on non-leaf nodes."
+          unit.error(clazz.pos, ( 
+            "case class `%s' has case ancestor `%s'. Case-to-case inheritance is prohibited."+
+            " To overcome this limitation use extractors to pattern match on non-leaf nodes."
           ).format(clazz, ancestor))
         }
       }

test/files/neg/caseinherit.check

@@ -1,10 +1,10 @@
-caseinherit.scala:2: error: case class `class B' has case ancestor `class A'.  Case-to-case inheritance has potentially dangerous bugs which are unlikely to be fixed.  You are strongly encouraged to instead use extractors to pattern match on non-leaf nodes.
+caseinherit.scala:2: error: case class `class B' has case ancestor `class A'. Case-to-case inheritance is prohibited. To overcome this limitation use extractors to pattern match on non-leaf nodes.
 case class B(y: Int) extends A(y)
            ^
-caseinherit.scala:3: error: case class `object Bippy' has case ancestor `class A'.  Case-to-case inheritance has potentially dangerous bugs which are unlikely to be fixed.  You are strongly encouraged to instead use extractors to pattern match on non-leaf nodes.
+caseinherit.scala:3: error: case class `object Bippy' has case ancestor `class A'. Case-to-case inheritance is prohibited. To overcome this limitation use extractors to pattern match on non-leaf nodes.
 case object Bippy extends A(55)
             ^
-caseinherit.scala:6: error: case class `class Dingus' has case ancestor `class A'.  Case-to-case inheritance has potentially dangerous bugs which are unlikely to be fixed.  You are strongly encouraged to instead use extractors to pattern match on non-leaf nodes.
+caseinherit.scala:6: error: case class `class Dingus' has case ancestor `class A'. Case-to-case inheritance is prohibited. To overcome this limitation use extractors to pattern match on non-leaf nodes.
 case class Dingus(y: Int) extends Innocent
            ^
 three errors found

test/files/neg/caseinherit.flags

@@ -0,0 +1,4 @@
+t0816.scala:5: error: case class `class Ctest' has case ancestor `class Btest'. Case-to-case inheritance is prohibited. To overcome this limitation use extractors to pattern match on non-leaf nodes.
+case class Ctest(override val data: String) extends Btest(data, true)
+           ^
+one error found

test/files/neg/t0816.check

@@ -0,0 +1,4 @@
+t425.scala:3: error: case class `class B' has case ancestor `class A'. Case-to-case inheritance is prohibited. To overcome this limitation use extractors to pattern match on non-leaf nodes.
+  case class B(override val x: Int, y: Double) extends A(x)
+             ^
+one error found