Merge pull request scala#4252 from retronym/ticket/9050

SI-9050 Fix crasher with value classes, recursion

Author: lrytz

src/reflect/scala/reflect/internal/Trees.scala

@@ -1576,6 +1576,7 @@ trait Trees extends api.Trees {
    */
   class TreeSymSubstituter(from: List[Symbol], to: List[Symbol]) extends Transformer {
     val symSubst = new SubstSymMap(from, to)
+    private var mutatedSymbols: List[Symbol] = Nil
     override def transform(tree: Tree): Tree = {
       def subst(from: List[Symbol], to: List[Symbol]) {
         if (!from.isEmpty)
@@ -1594,6 +1595,7 @@ trait Trees extends api.Trees {
                 |TreeSymSubstituter: updated info of symbol ${tree.symbol}
                 |  Old: ${showRaw(tree.symbol.info, printTypes = true, printIds = true)}
                 |  New: ${showRaw(newInfo, printTypes = true, printIds = true)}""")
+              mutatedSymbols ::= tree.symbol
               tree.symbol updateInfo newInfo
             }
           case _          =>
@@ -1613,7 +1615,23 @@ trait Trees extends api.Trees {
       } else
         super.transform(tree)
     }
-    def apply[T <: Tree](tree: T): T = transform(tree).asInstanceOf[T]
+    def apply[T <: Tree](tree: T): T = {
+      val tree1 = transform(tree)
+      invalidateSingleTypeCaches(tree1)
+      tree1.asInstanceOf[T]
+    }
+    private def invalidateSingleTypeCaches(tree: Tree): Unit = {
+      if (mutatedSymbols.nonEmpty)
+        for (t <- tree)
+          for (tp <- t.tpe) {
+            tp match {
+              case s: SingleType if mutatedSymbols contains s.sym =>
+                s.underlyingPeriod = NoPeriod
+                s.underlyingCache = NoType
+              case _ =>
+            }
+          }
+    }
     override def toString() = "TreeSymSubstituter/" + substituterString("Symbol", "Symbol", from, to)
   }
 

test/files/pos/t9050.scala

@@ -0,0 +1,13 @@
+final class Mu[F](val value: Any) extends AnyVal {
+  def cata(f: F) {
+    // crash
+    ((y: Mu[F]) => y.cata(f))
+    // crash
+    def foo(x : Mu[F]) = x.cata(f)
+
+    // // okay
+    def x: Mu[F] = ???
+    (() => x.cata(f))
+    assert(true, cata(f))
+  }
+}