Merge pull request #1526 from paulp/value-classes/6534-equals

New take on SI-6534, value classes.

1 files changed, 18 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala b/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala
index 001acc7a80..6afc823376 100644
--- a/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/SyntheticMethods.scala
@@ -326,7 +326,24 @@ trait SyntheticMethods extends ast.TreeDSL {
         else Nil
       )
 
-      def impls = for ((m, impl) <- methods ; if !hasOverridingImplementation(m)) yield impl()
+      /** Always generate overrides for equals and hashCode in value classes,
+       *  so they can appear in universal traits without breaking value semantics.
+       */
+      def impls = {
+        def shouldGenerate(m: Symbol) = {
+          !hasOverridingImplementation(m) || {
+            clazz.isDerivedValueClass && (m == Any_hashCode || m == Any_equals) && {
+              if (settings.lint.value) {
+                (clazz.info nonPrivateMember m.name) filter (m => (m.owner != AnyClass) && (m.owner != clazz) && !m.isDeferred) andAlso { m =>
+                  currentUnit.warning(clazz.pos, s"Implementation of ${m.name} inherited from ${m.owner} overridden in $clazz to enforce value class semantics")
+                }
+              }
+              true
+            }
+          }
+        }
+        for ((m, impl) <- methods ; if shouldGenerate(m)) yield impl()
+      }
       def extras = (
         if (needsReadResolve) {
           // Aha, I finally decoded the original comment.