Merge pull request #2432 from retronym/ticket/delayed-init-ref

Warn on selection of vals from DelayedInit subclasses.

4 files changed, 64 insertions, 0 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
index 7f8aeceeec..4933b8e0cb 100644
--- a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
@@ -1411,6 +1411,16 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
       }
     }
 
+    private def checkDelayedInitSelect(qual: Tree, sym: Symbol, pos: Position) = {
+      def isLikelyUninitialized = (
+           (sym.owner isSubClass DelayedInitClass)
+        && !qual.tpe.isInstanceOf[ThisType]
+        && sym.accessedOrSelf.isVal
+      )
+      if (settings.lint.value && isLikelyUninitialized)
+        unit.warning(pos, s"Selecting ${sym} from ${sym.owner}, which extends scala.DelayedInit, is likely to yield an uninitialized value")
+    }
+
     private def lessAccessible(otherSym: Symbol, memberSym: Symbol): Boolean = (
          (otherSym != NoSymbol)
       && !otherSym.isProtected
@@ -1610,6 +1620,7 @@ abstract class RefChecks extends InfoTransform with scala.reflect.internal.trans
       if(settings.Xmigration.value != NoScalaVersion)
         checkMigration(sym, tree.pos)
       checkCompileTimeOnly(sym, tree.pos)
+      checkDelayedInitSelect(qual, sym, tree.pos)
 
       if (sym eq NoSymbol) {
         unit.warning(tree.pos, "Select node has NoSymbol! " + tree + " / " + tree.tpe)
diff --git a/test/files/neg/delayed-init-ref.check b/test/files/neg/delayed-init-ref.check
new file mode 100644
index 0000000000..42ccabed1b
--- /dev/null
+++ b/test/files/neg/delayed-init-ref.check
@@ -0,0 +1,10 @@
+delayed-init-ref.scala:17: error: Selecting value vall from object O, which extends scala.DelayedInit, is likely to yield an uninitialized value
+  println(O.vall)     // warn
+            ^
+delayed-init-ref.scala:19: error: Selecting value vall from object O, which extends scala.DelayedInit, is likely to yield an uninitialized value
+  println(vall)       // warn
+          ^
+delayed-init-ref.scala:40: error: Selecting value foo from trait UserContext, which extends scala.DelayedInit, is likely to yield an uninitialized value
+    println({locally(()); this}.foo)  // warn (spurious, but we can't discriminate)
+                                ^
+three errors found
diff --git a/test/files/neg/delayed-init-ref.flags b/test/files/neg/delayed-init-ref.flags
new file mode 100644
index 0000000000..7949c2afa2
--- /dev/null
+++ b/test/files/neg/delayed-init-ref.flags
@@ -0,0 +1 @@
+-Xlint -Xfatal-warnings
diff --git a/test/files/neg/delayed-init-ref.scala b/test/files/neg/delayed-init-ref.scala
new file mode 100644
index 0000000000..f2aa804e28
--- /dev/null
+++ b/test/files/neg/delayed-init-ref.scala
@@ -0,0 +1,42 @@
+trait T {
+  val traitVal = ""
+}
+
+object O extends App with T {
+  val vall = ""
+  lazy val lazyy = ""
+  def deff = ""
+
+  println(vall)       // no warn
+  new {
+    println(vall)     // no warn
+  }
+}
+
+object Client {
+  println(O.vall)     // warn
+  import O.vall
+  println(vall)       // warn
+
+  println(O.lazyy)    // no warn
+  println(O.deff)     // no warn
+  println(O.traitVal) // no warn
+}
+
+// Delayed init usage pattern from Specs2
+// See: https://groups.google.com/d/msg/scala-sips/wP6dL8nIAQs/ogjoPE-MSVAJ
+trait Before extends DelayedInit {
+  def before()
+  override def delayedInit(x: => Unit): Unit = { before; x }
+}
+object Spec {
+  trait UserContext extends Before {
+    def before() = ()
+    val foo = "foo"
+  }
+  new UserContext {
+    println(foo)                      // no warn
+    println(this.foo)                 // no warn
+    println({locally(()); this}.foo)  // warn (spurious, but we can't discriminate)
+  }
+}