Make isSeparateCompiled... robust against rogue phase time travel

We don't hit this code path during bootstrapping, but we could
conceivably hit it with macros or compiler plugins peering into
the future through atPhase before refchecks as run.

Also rename a method to reflect the generality of the info
transform (it does more than mixin, now.)

2 files changed, 9 insertions, 3 deletions

diff --git a/src/compiler/scala/tools/nsc/transform/Fields.scala b/src/compiler/scala/tools/nsc/transform/Fields.scala
index c39491cf9e..b8b2b64fb8 100644
--- a/src/compiler/scala/tools/nsc/transform/Fields.scala
+++ b/src/compiler/scala/tools/nsc/transform/Fields.scala
@@ -305,7 +305,7 @@ abstract class Fields extends InfoTransform with ast.TreeDSL with TypingTransfor
       lazyCallingSuper setInfo tp
     }
 
-    private def needsMixin(cls: Symbol): Boolean = {
+    private def classNeedsInfoTransform(cls: Symbol): Boolean = {
       !(cls.isPackageClass || cls.isJavaDefined) && (currentRun.compiles(cls) || refChecks.isSeparatelyCompiledScalaSuperclass(cls))
     }
 
@@ -365,7 +365,7 @@ abstract class Fields extends InfoTransform with ast.TreeDSL with TypingTransfor
         } else tp
 
 
-      case tp@ClassInfoType(parents, oldDecls, clazz) if !needsMixin(clazz) => tp
+      case tp@ClassInfoType(parents, oldDecls, clazz) if !classNeedsInfoTransform(clazz) => tp
 
       // mix in fields & accessors for all mixed in traits
       case tp@ClassInfoType(parents, oldDecls, clazz) =>
diff --git a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
index 24b4334ec4..106b076eef 100644
--- a/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/RefChecks.scala
@@ -96,7 +96,13 @@ abstract class RefChecks extends Transform {
   }
 
   private val separatelyCompiledScalaSuperclass = perRunCaches.newAnyRefMap[Symbol, Unit]()
-  final def isSeparatelyCompiledScalaSuperclass(sym: Symbol) = separatelyCompiledScalaSuperclass.contains(sym)
+  final def isSeparatelyCompiledScalaSuperclass(sym: Symbol) = if (globalPhase.refChecked){
+    separatelyCompiledScalaSuperclass.contains(sym)
+  } else {
+    // conservative approximation in case someone in pre-refchecks phase asks for `exitingFields(someClass.info)`
+    // and we haven't run the refchecks tree transform which populates `separatelyCompiledScalaSuperclass`
+    false
+  }
 
   class RefCheckTransformer(unit: CompilationUnit) extends Transformer {