Merge pull request scala#3614 from retronym/ticket/8196

SI-8196 Runtime reflection robustness for STATIC impl details

Author: retronym

bincompat-forward.whitelist.conf

@@ -173,6 +173,11 @@ filter {
         {
             matchName="scala.reflect.runtime.SymbolLoaders.isInvalidClassName"
             problemName=MissingMethodProblem
+        },
+        {
+            matchName="scala.reflect.runtime.JavaMirrors#JavaMirror.scala$reflect$runtime$JavaMirrors$JavaMirror$$followStatic"
+            problemName=MissingMethodProblem
         }
+
     ]
 }

src/reflect/scala/reflect/runtime/JavaMirrors.scala

@@ -685,8 +685,7 @@ private[reflect] trait JavaMirrors extends internal.SymbolTable with api.JavaUni
           module.moduleClass setInfo new ClassInfoType(List(), newScope, module.moduleClass)
         }
 
-        def enter(sym: Symbol, mods: Int) =
-          (if (jModifier.isStatic(mods)) module.moduleClass else clazz).info.decls enter sym
+        def enter(sym: Symbol, mods: Int) = followStatic(clazz, module, mods).info.decls enter sym
 
         def enterEmptyCtorIfNecessary(): Unit = {
           if (jclazz.getConstructors.isEmpty)
@@ -733,8 +732,12 @@ private[reflect] trait JavaMirrors extends internal.SymbolTable with api.JavaUni
      * If Java modifiers `mods` contain STATIC, return the module class
      *  of the companion module of `clazz`, otherwise the class `clazz` itself.
      */
-    private def followStatic(clazz: Symbol, mods: Int) =
-      if (jModifier.isStatic(mods)) clazz.companionModule.moduleClass else clazz
+    private def followStatic(clazz: Symbol, mods: Int): Symbol = followStatic(clazz, clazz.companionModule, mods)
+
+    private def followStatic(clazz: Symbol, module: Symbol, mods: Int): Symbol =
+      // SI-8196 `orElse(clazz)` needed for implementation details of the backend, such as the static
+      //         field containing the cache for structural calls.
+      if (jModifier.isStatic(mods)) module.moduleClass.orElse(clazz) else clazz
 
   /** Methods which need to be treated with care
    *  because they either are getSimpleName or call getSimpleName:

test/files/run/t8196.check

@@ -0,0 +1,3 @@
+Scope{
+  final private val f1: Int
+}

test/files/run/t8196.scala

@@ -0,0 +1,51 @@
+import scala.reflect.runtime.{ universe => ru }
+
+object Test extends App {
+ 
+  trait FormTrait {
+
+    val runtimeMirror = ru.runtimeMirror(this.getClass.getClassLoader)
+    val instanceMirror = runtimeMirror.reflect(this)
+    val members = instanceMirror.symbol.typeSignature.members
+    def fields = members.filter(_.typeSignature <:< ru.typeOf[Int])
+  }
+ 
+  val f = () => {
+ 
+    class Form1 extends FormTrait {
+      val f1 = 5
+    }
+    val form1 = new Form1
+ 
+    println(form1.fields)
+ 
+    val form2 = new FormTrait {
+      val g1 = new Form1
+    }
+ 
+    form2.g1 // comment this line in order to make the test pass
+    ()
+  }
+
+  val g = () => {
+    // Reported as SI-8195, same root cause
+    trait Form {
+ 
+      private val runtimeMirror = ru.runtimeMirror(this.getClass.getClassLoader)
+      private val instanceMirror = runtimeMirror.reflect(this)
+      private val members = instanceMirror.symbol.typeSignature.members
+ 
+    }
+ 
+    val f1 = new Form {
+      val a = 1
+    }
+ 
+    val f2 = new Form {
+      val b = f1.a
+    }
+  }
+
+  f() 
+  g() 
+}