Refactor transform of case apply in refchecks

I've identified a dead call to `transformCaseApply` that
seems to date back to Scala 2.6 vintages, in which case
factory methods were a fictional companion method, rather
than a real apply method in a companion module.

This commit adds an abort in that code path to aide code
review (if our test suite still passes, we know that I've
removed dead code, rather than silently changing behaviour.)
The following commit will remove it altogether

I then inlined a slightly clunky abstraction in the two
remaining calls to `transformCaseApply`. It was getting in the
way of a clean fix to SI-9546, the topic of the next commit.

1 files changed, 30 insertions, 28 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
index c5abd756f8..f2607b6bde 100644
--- a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
@@ -1503,9 +1503,8 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
       }
     }
 
-    private def transformCaseApply(tree: Tree, ifNot: => Unit) = {
+    private def isSimpleCaseApply(tree: Tree): Boolean = {
       val sym = tree.symbol
-
       def isClassTypeAccessible(tree: Tree): Boolean = tree match {
         case TypeApply(fun, targs) =>
           isClassTypeAccessible(fun)
@@ -1513,31 +1512,26 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
           ( // SI-4859 `CaseClass1().InnerCaseClass2()` must not be rewritten to `new InnerCaseClass2()`;
             //          {expr; Outer}.Inner() must not be rewritten to `new Outer.Inner()`.
             treeInfo.isQualifierSafeToElide(module) &&
-            // SI-5626 Classes in refinement types cannot be constructed with `new`. In this case,
-            // the companion class is actually not a ClassSymbol, but a reference to an abstract type.
-            module.symbol.companionClass.isClass
-          )
+              // SI-5626 Classes in refinement types cannot be constructed with `new`. In this case,
+              // the companion class is actually not a ClassSymbol, but a reference to an abstract type.
+              module.symbol.companionClass.isClass
+            )
       }
 
-      val doTransform =
-        sym.isSourceMethod &&
+      sym.isSourceMethod &&
         sym.isCase &&
         sym.name == nme.apply &&
         isClassTypeAccessible(tree) &&
         !tree.tpe.resultType.typeSymbol.primaryConstructor.isLessAccessibleThan(tree.symbol)
+    }
 
-      if (doTransform) {
-        tree foreach {
-          case i@Ident(_) =>
-            enterReference(i.pos, i.symbol) // SI-5390 need to `enterReference` for `a` in `a.B()`
-          case _ =>
-        }
-        toConstructor(tree.pos, tree.tpe)
-      }
-      else {
-        ifNot
-        tree
+    private def transformCaseApply(tree: Tree) = {
+      tree foreach {
+        case i@Ident(_) =>
+          enterReference(i.pos, i.symbol) // SI-5390 need to `enterReference` for `a` in `a.B()`
+        case _ =>
       }
+      toConstructor(tree.pos, tree.tpe)
     }
 
     private def transformApply(tree: Apply): Tree = tree match {
@@ -1577,12 +1571,15 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
         // term should have been eliminated by super accessors
         assert(!(qual.symbol.isTrait && sym.isTerm && mix == tpnme.EMPTY), (qual.symbol, sym, mix))
 
-      transformCaseApply(tree,
+      if (isSimpleCaseApply(tree)) {
+        transformCaseApply(tree)
+      } else {
         qual match {
           case Super(_, mix)  => checkSuper(mix)
           case _              =>
         }
-      )
+        tree
+      }
     }
     private def transformIf(tree: If): Tree = {
       val If(cond, thenpart, elsepart) = tree
@@ -1706,7 +1703,10 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
 
           case TypeApply(fn, args) =>
             checkBounds(tree, NoPrefix, NoSymbol, fn.tpe.typeParams, args map (_.tpe))
-            transformCaseApply(tree, ())
+            if (isSimpleCaseApply(tree))
+              transformCaseApply(tree)
+            else
+              tree
 
           case x @ Apply(_, _)  =>
             transformApply(x)
@@ -1725,12 +1725,14 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
 
           case Ident(name) =>
             checkUndesiredProperties(sym, tree.pos)
-            transformCaseApply(tree,
-              if (name != nme.WILDCARD && name != tpnme.WILDCARD_STAR) {
-                assert(sym != NoSymbol, "transformCaseApply: name = " + name.debugString + " tree = " + tree + " / " + tree.getClass) //debug
-                enterReference(tree.pos, sym)
-              }
-            )
+            if (isSimpleCaseApply(tree)) {
+              abort("case factory methods are now always selected from prefix (since https://github.com/scala/scala/commit/76c06b4)")
+            }
+            if (name != nme.WILDCARD && name != tpnme.WILDCARD_STAR) {
+              assert(sym != NoSymbol, "transformCaseApply: name = " + name.debugString + " tree = " + tree + " / " + tree.getClass) //debug
+              enterReference(tree.pos, sym)
+            }
+            tree
 
           case x @ Select(_, _) =>
             transformSelect(x)