Merge pull request #5730 from adriaanm/userdefined-apply-211

Allow user-defined apply/unapply method in case class companion

1 files changed, 83 insertions, 12 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Namers.scala b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
index ee64a6646f..69b8cb12e6 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Namers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
@@ -610,7 +610,15 @@ trait Namers extends MethodSynthesis {
       noDuplicates(selectors map (_.rename), AppearsTwice)
     }
 
-    def enterCopyMethod(copyDef: DefDef): Symbol = {
+    class CompleterWrapper(completer: TypeCompleter) extends TypeCompleter {
+      val tree = completer.tree
+
+      override def complete(sym: Symbol): Unit = {
+        completer.complete(sym)
+      }
+    }
+
+    def copyMethodCompleter(copyDef: DefDef): TypeCompleter = {
       val sym      = copyDef.symbol
       val lazyType = completerOf(copyDef)
 
@@ -629,13 +637,72 @@ trait Namers extends MethodSynthesis {
         )
       }
 
-      sym setInfo {
-        mkTypeCompleter(copyDef) { sym =>
-          assignParamTypes()
-          lazyType complete sym
+      mkTypeCompleter(copyDef) { sym =>
+        assignParamTypes()
+        lazyType complete sym
+      }
+    }
+
+    // for apply/unapply, which may need to disappear when they clash with a user-defined method of matching signature
+    def applyUnapplyMethodCompleter(un_applyDef: DefDef, companionContext: Context): TypeCompleter =
+      new CompleterWrapper(completerOf(un_applyDef)) {
+        override def complete(sym: Symbol): Unit = {
+          assert(sym hasAllFlags CASE | SYNTHETIC, sym.defString)
+
+          super.complete(sym)
+
+          // owner won't be locked
+          val ownerInfo = companionContext.owner.info
+
+          // If there's a same-named locked symbol, we're currently completing its signature.
+          // If `scopePartiallyCompleted`, the program is known to have a type error, since
+          // this means a user-defined method is missing a result type while its rhs refers to `sym` or an overload.
+          // This is an error because overloaded/recursive methods must have a result type.
+          // The method would be overloaded if its signature, once completed, would not match the synthetic method's,
+          // or recursive if it turned out we should unlink our synthetic method (matching sig).
+          // In any case, error out. We don't unlink the symbol so that `symWasOverloaded` says yes,
+          // which would be wrong if the method is in fact recursive, but it seems less confusing.
+          val scopePartiallyCompleted = new HasMember(ownerInfo, sym.name, BridgeFlags | SYNTHETIC, LOCKED).apply()
+
+          // Check `scopePartiallyCompleted` first to rule out locked symbols from the owner.info.member call,
+          // as FindMember will call info on a locked symbol (while checking type matching to assemble an overloaded type),
+          // and throw a TypeError, so that we are aborted.
+          // Do not consider deferred symbols, as suppressing our concrete implementation would be an error regardless
+          // of whether the signature matches (if it matches, we omitted a valid implementation, if it doesn't,
+          // we would get an error for the missing implementation it isn't implemented by some overload other than our synthetic one)
+          val suppress = scopePartiallyCompleted || {
+            // can't exclude deferred members using DEFERRED flag here (TODO: why?)
+            val userDefined = ownerInfo.memberBasedOnName(sym.name, BridgeFlags | SYNTHETIC)
+
+            (userDefined != NoSymbol) && {
+              assert(userDefined != sym)
+              val alts = userDefined.alternatives // could be just the one, if this member isn't overloaded
+              // don't compute any further `memberInfo`s if there's an error somewhere
+              alts.exists(_.isErroneous) || {
+                val self = companionContext.owner.thisType
+                val memberInfo = self.memberInfo(sym)
+                alts.exists(alt => !alt.isDeferred && (self.memberInfo(alt) matches memberInfo))
+              }
+            }
+          }
+
+          if (suppress) {
+            sym setInfo ErrorType
+            sym setFlag IS_ERROR
+
+            // Don't unlink in an error situation to generate less confusing error messages.
+            // Ideally, our error reporting would distinguish overloaded from recursive user-defined apply methods without signature,
+            // but this would require some form of partial-completion of method signatures, so that we can
+            // know what the argument types were, even though we can't complete the result type, because
+            // we hit a cycle while trying to compute it (when we get here with locked user-defined symbols, we
+            // are in the complete for that symbol, and thus the locked symbol has not yet received enough info;
+            // I hesitate to provide more info, because it would involve a WildCard or something for its result type,
+            // which could upset other code paths)
+            if (!scopePartiallyCompleted)
+              companionContext.scope.unlink(sym)
+          }
         }
       }
-    }
 
     def completerOf(tree: Tree): TypeCompleter = {
       val mono = namerOf(tree.symbol) monoTypeCompleter tree
@@ -697,11 +764,15 @@ trait Namers extends MethodSynthesis {
         val bridgeFlag = if (mods hasAnnotationNamed tpnme.bridgeAnnot) BRIDGE | ARTIFACT else 0
         val sym = assignAndEnterSymbol(tree) setFlag bridgeFlag
 
-        if (name == nme.copy && sym.isSynthetic)
-          enterCopyMethod(tree)
-        else
-          sym setInfo completerOf(tree)
-    }
+        val completer =
+          if (sym hasFlag SYNTHETIC) {
+            if (name == nme.copy) copyMethodCompleter(tree)
+            else if (sym hasFlag CASE) applyUnapplyMethodCompleter(tree, context)
+            else completerOf(tree)
+          } else completerOf(tree)
+
+        sym setInfo completer
+      }
 
     def enterClassDef(tree: ClassDef) {
       val ClassDef(mods, _, _, impl) = tree
@@ -1351,7 +1422,7 @@ trait Namers extends MethodSynthesis {
 
             val defTpt =
               // don't mess with tpt's of case copy default getters, because assigning something other than TypeTree()
-              // will break the carefully orchestrated naming/typing logic that involves enterCopyMethod and caseClassCopyMeth
+              // will break the carefully orchestrated naming/typing logic that involves copyMethodCompleter and caseClassCopyMeth
               if (meth.isCaseCopy) TypeTree()
               else {
                 // If the parameter type mentions any type parameter of the method, let the compiler infer the