Classfile parser and unpickler require class and module symbol arguments

In SymbolLoaders, when seeing a classfile `Foo.class`, we always
(unconditionally) create 3 symbols: a class, a module and a module
class. Some symbols get invalidated later (`.exists`).

Until now, the classfile parser (and unpickler) received the "root"
symbol as argument, which is the symbol whose type is being completed.
This is either the class symbol or the module symbol.

The classfile parser would then try to lookup the other symbol through
`root.companionClass` or `root.companionModule`. Howver, this lookup can
fail. One example is scala-dev#248: when a type alias (in a package
object) shadows a class symbol, `companionClass` will fail.

The implementations of the  classfile parser / unpickler assume that
both the `clazz` and the `staticModule` symbols are available. This
change makes sure that they are always passed in explicitly.

Before this patch, in the example of scala-dev#248, the `classRoot` of
the unpickler was NoSymbol. This caused a bug when unpickling the
module class symbol, causing a second module class symbol to be created
mistakingly. The next commit cleans up this logic, more details there.
This second symbol would then cause the crash in the backend because it
doesn't have an `associatedFile`, therefore `isCoDefinedWith` would
spuriously return `true`.

1 files changed, 9 insertions, 12 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala b/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
index e69c9f816a..6d5b697925 100644
--- a/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
+++ b/src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala
@@ -132,17 +132,12 @@ abstract class ClassfileParser {
     finally loaders.parentsLevel -= 1
   }
 
-  def parse(file: AbstractFile, root: Symbol): Unit = {
-    debuglog("[class] >> " + root.fullName)
-
+  def parse(file: AbstractFile, clazz: Symbol, module: Symbol): Unit = {
     this.file = file
-    pushBusy(root) {
+    pushBusy(clazz) {
       this.in           = new AbstractFileReader(file)
-      this.clazz        = if (root.isModule) root.companionClass else root
-      // WARNING! do no use clazz.companionModule to find staticModule.
-      // In a situation where root can be defined, but its companionClass not,
-      // this would give incorrect results (see SI-5031 in separate compilation scenario)
-      this.staticModule = if (root.isModule) root else root.companionModule
+      this.clazz        = clazz
+      this.staticModule = module
       this.isScala      = false
 
       parseHeader()
@@ -1020,7 +1015,6 @@ abstract class ClassfileParser {
 
     def enterClassAndModule(entry: InnerClassEntry, file: AbstractFile) {
       def jflags      = entry.jflags
-      val completer   = new loaders.ClassfileLoader(file)
       val name        = entry.originalName
       val sflags      = jflags.toScalaFlags
       val owner       = ownerForFlags(jflags)
@@ -1031,8 +1025,11 @@ abstract class ClassfileParser {
       val (innerClass, innerModule) = if (file == NoAbstractFile) {
         (newStub(name.toTypeName), newStub(name.toTermName))
       } else {
-        val cls = owner.newClass(name.toTypeName, NoPosition, sflags) setInfo completer
-        val mod = owner.newModule(name.toTermName, NoPosition, sflags) setInfo completer
+        val cls = owner.newClass(name.toTypeName, NoPosition, sflags)
+        val mod = owner.newModule(name.toTermName, NoPosition, sflags)
+        val completer = new loaders.ClassfileLoader(file, cls, mod)
+        cls setInfo completer
+        mod setInfo completer
         mod.moduleClass setInfo loaders.moduleClassLoader
         List(cls, mod.moduleClass) foreach (_.associatedFile = file)
         (cls, mod)