Merge pull request scala#4341 from retronym/ticket/9157

adriaanm · adriaanm · commit ea17de17dd8f · 2015-02-18T10:40:32.000-08:00
SI-9157 Avoid exponential blowup with chained type projections
diff --git a/src/compiler/scala/tools/nsc/typechecker/TreeCheckers.scala b/src/compiler/scala/tools/nsc/typechecker/TreeCheckers.scala
@@ -266,7 +266,6 @@ abstract class TreeCheckers extends Analyzer {
 
       if (tree ne typed)
         treesDiffer(tree, typed)
-
       tree
     }
 
diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala
@@ -1976,13 +1976,13 @@ trait Types
      * usage scenario.
      */
     private var relativeInfoCache: Type = _
-    private var memberInfoCache: Type = _
+    private var relativeInfoPeriod: Period = NoPeriod
 
-    private[Types] def relativeInfo = {
-      val memberInfo = pre.memberInfo(sym)
-      if (relativeInfoCache == null || (memberInfo ne memberInfoCache)) {
-        memberInfoCache = memberInfo
+    private[Types] def relativeInfo = /*trace(s"relativeInfo(${safeToString}})")*/{
+      if (relativeInfoPeriod != currentPeriod) {
+        val memberInfo = pre.memberInfo(sym)
         relativeInfoCache = transformInfo(memberInfo)
+        relativeInfoPeriod = currentPeriod
       }
       relativeInfoCache
     }
diff --git a/test/files/pos/t9157.scala b/test/files/pos/t9157.scala
@@ -0,0 +1,13 @@
+trait Flow[-In, +Out] {
+  type Repr[+O] <: Flow[In, O]
+  def map: Repr[String]
+}
+
+class Test {
+  // typechecking was exponentially slow wrt the number of projections here.
+  def slowFlow(
+    f: Flow[String,String]#Repr[String]#Repr[String]#Repr[String]#Repr[String]#Repr[String]#Repr[String]#Repr[String]#Repr[String]#Repr[String]#Repr[String]#Repr[String]
+  ) = {
+    f.map
+  }
+}

Original file line number	Diff line number	Diff line change
`@@ -266,7 +266,6 @@ abstract class TreeCheckers extends Analyzer {`
`266`	`266`
`267`	`267`	`if (tree ne typed)`
`268`	`268`	`treesDiffer(tree, typed)`
`269`		`-`
`270`	`269`	`tree`
`271`	`270`	`}`
`272`	`271`