Fixes typelevel#290 (deadlock under 2.12 during property initialization)

jvm/src/test/scala/org/scalacheck/LazyPropertiesSpecification.scala

@@ -0,0 +1,26 @@
+/*-------------------------------------------------------------------------*\
+**  ScalaCheck                                                             **
+**  Copyright (c) 2007-2016 Rickard Nilsson. All rights reserved.          **
+**  http://www.scalacheck.org                                              **
+**                                                                         **
+**  This software is released under the terms of the Revised BSD License.  **
+**  There is NO WARRANTY. See the file LICENSE for the full text.          **
+\*------------------------------------------------------------------------ */
+
+package org.scalacheck
+
+object LazyPropertiesSpecification extends Properties("Properties.lazy registration") {
+
+  property("properties registered lazily") = {
+    var evaluated = false
+    val p = new Properties("P") {
+      property("p") = {
+        evaluated = true
+        Prop.proved
+      }
+    }
+    evaluated == false
+  }
+
+}
+

src/main/scala/org/scalacheck/Prop.scala

@@ -300,6 +300,9 @@ object Prop {
   /** Create a property from a boolean value */
   def apply(b: Boolean): Prop = if(b) proved else falsified
 
+  /** Create a prop that evaluates the by-name argument on each application. */
+  def suspend(p: => Prop): Prop = apply(prms => p(prms))
+
 
   // Implicits
 

src/main/scala/org/scalacheck/Properties.scala

@@ -93,7 +93,13 @@ class Properties(val name: String) {
    *  }}}
    */
   sealed class PropertySpecifier() {
-    def update(propName: String, p: Prop) = props += ((name+"."+propName, p))
+    // TODO: Delete this in 1.14 -- kept for binary compat with 1.13.3 and prior
+    protected def update(propName: String, p: Prop) = {
+      props += ((name+"."+propName, p))
+    }
+    def update(propName: String, p: => Prop) = {
+      props += ((name+"."+propName, Prop.suspend(p)))
+    }
   }
 
   lazy val property = new PropertySpecifier()