From d21f90c2cec03113a7d5971d68bb2d934d8d751f Mon Sep 17 00:00:00 2001
From: Jason Zaugg <jzaugg@gmail.com>
Date: Tue, 2 Apr 2013 14:58:46 +0200
Subject: [PATCH] SI-7147 Diagnostic for unexplained assertion in presentation
 compiler.

We don't have a reproducible test for this, so the best we can
do is beef up the assertion to shine a little light on the problem.
---
 .../scala/tools/nsc/symtab/SymbolLoaders.scala        | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/compiler/scala/tools/nsc/symtab/SymbolLoaders.scala b/src/compiler/scala/tools/nsc/symtab/SymbolLoaders.scala
index 348c7f688f86..9e5186b73113 100644
--- a/src/compiler/scala/tools/nsc/symtab/SymbolLoaders.scala
+++ b/src/compiler/scala/tools/nsc/symtab/SymbolLoaders.scala
@@ -97,8 +97,15 @@ abstract class SymbolLoaders {
     val clazz = enterClass(root, name, completer)
     val module = enterModule(root, name, completer)
     if (!clazz.isAnonymousClass) {
-      assert(clazz.companionModule == module, module)
-      assert(module.companionClass == clazz, clazz)
+      // Diagnostic for SI-7147
+      def msg: String = {
+        def symLocation(sym: Symbol) = if (sym == null) "null" else s"${clazz.fullLocationString} (from ${clazz.associatedFile})"
+        sm"""Inconsistent class/module symbol pair for `$name` loaded from ${symLocation(root)}.
+            |clazz = ${symLocation(clazz)}; clazz.companionModule = ${clazz.companionModule}
+            |module = ${symLocation(module)}; module.companionClass = ${module.companionClass}"""
+      }
+      assert(clazz.companionModule == module, msg)
+      assert(module.companionClass == clazz, msg)
     }
   }