Making the order of constructors returned deterministic

json4s · May 27, 2020 · 70c7c5e · 70c7c5e
1 parent acbc81e
commit 70c7c5e
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Showing 2 changed files with 32 additions and 3 deletions.
diff --git a/core/src/main/scala/org/json4s/reflect/Reflector.scala b/core/src/main/scala/org/json4s/reflect/Reflector.scala
@@ -132,7 +132,12 @@ object Reflector {
         case None => scala.Array[Method]()
       }
       val applyExecutables = applyMethods.map{ m => new Executable(m) }
-      constructorDescriptors ++ createConstructorDescriptors(applyExecutables)
+      val all = constructorDescriptors ++ createConstructorDescriptors(applyExecutables)
+
+      // https://github.com/json4s/json4s/issues/371 no actual requirements for the order are known, but
+      // deterministic ordering regardless of non-determinism by java.reflect is needed
+      all.toList.sortBy(c =>
+        (!c.isPrimary, c.constructor.constructor == null, -c.params.size, c.toString))
     }
 
     def createConstructorDescriptors(ccs: Iterable[Executable]): Seq[ConstructorDescriptor] = {

diff --git a/tests/src/test/scala/org/json4s/reflect/ReflectorSpec.scala b/tests/src/test/scala/org/json4s/reflect/ReflectorSpec.scala
@@ -2,8 +2,7 @@ package org.json4s.reflect
 
 import org.json4s.reflect
 import org.specs2.mutable.Specification
-
-import ReflectorSpec.{Person, Dog, Cat}
+import ReflectorSpec.{Cat, Dog, Person}
 
 object ReflectorSpec {
   case class Person(firstName: String, lastName: String) {
@@ -46,6 +45,8 @@ class ReflectorSpec extends Specification {
       // the only human-visible constructor is visible as two - the constructor and the apply method
       descriptor.constructors.size must_== 2
       descriptor.constructors.count(_.isPrimary) must_== 1
+      descriptor.constructors(0).isPrimary must_== true
+      descriptor.constructors(1).isPrimary must_== false
     }
 
     "denote the annotated constructor as primary even if multiple exist" in {
@@ -55,5 +56,28 @@ class ReflectorSpec extends Specification {
       descriptor.constructors.size must_== 3
       descriptor.constructors.count(_.isPrimary) must_== 1
     }
+
+    "retrieve constructors of a class in a deterministic order" in {
+      val klass = Reflector.scalaTypeOf(classOf[Person])
+      val descriptor = Reflector.describe(klass).asInstanceOf[reflect.ClassDescriptor]
+
+      descriptor.constructors.size must_== 4
+      val first = descriptor.constructors(0)
+      val second = descriptor.constructors(1)
+      val third = descriptor.constructors(2)
+      val fourth = descriptor.constructors(3)
+
+      first.params.map(_.name) must_== Seq("firstName", "lastName")
+      first.constructor.method must_== null
+      first.constructor.constructor must_!= null
+
+      second.params.map(_.name) must_== Seq("age")
+
+      third.params.map(_.name) must_== Seq("firstName", "lastName")
+      third.constructor.method must_!= null
+      third.constructor.constructor must_== null
+
+      fourth.params.map(_.name) must_== Seq("email")
+    }
   }
 }