SI-2464 Resiliance against missing InnerClass attributes

A classfile in the wild related to Vaadin lacked the InnerClasses
attribute. As such, our class file parser treated a nested enum
class as top-level, which led to a crash when trying to find its
linked module.

More details of the investigation are available in the JIRA comments.

The test introduces a new facility to rewrite classfiles.

This commit turns this situation into a logged warning, rather
than crashing. Code by @paulp, test by yours truly.

1 files changed, 8 insertions, 4 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala b/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
index fb927d15d3..1e84c73633 100644
--- a/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
+++ b/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
@@ -588,10 +588,14 @@ abstract class ClassfileParser {
       // sealed java enums
       if (jflags.isEnum) {
         val enumClass = sym.owner.linkedClassOfClass
-        if (!enumClass.isSealed)
-          enumClass setFlag (SEALED | ABSTRACT)
-
-        enumClass addChild sym
+        enumClass match {
+          case NoSymbol =>
+            devWarning(s"no linked class for java enum $sym in ${sym.owner}. A referencing class file might be missing an InnerClasses entry.")
+          case linked =>
+            if (!linked.isSealed)
+              linked setFlag (SEALED | ABSTRACT)
+            linked addChild sym
+        }
       }
     }
   }