[SPARK-6595][SQL] MetastoreRelation should be a MultiInstanceRelation

Now that we have `DataFrame`s it is possible to have multiple copies in a single query plan.  As such, it needs to inherit from `MultiInstanceRelation` or self joins will break.  I also add better debugging errors when our self join handling fails in case there are future bugs.

Author: Michael Armbrust <michael@databricks.com>

Closes #5251 from marmbrus/multiMetaStore and squashes the following commits:

4272f6d [Michael Armbrust] [SPARK-6595][SQL] MetastoreRelation should be MuliInstanceRelation

2 files changed, 10 insertions, 2 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
index 44eceb0b37..ba1ac141b9 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
@@ -252,7 +252,15 @@ class Analyzer(catalog: Catalog,
           case oldVersion @ Aggregate(_, aggregateExpressions, _)
               if findAliases(aggregateExpressions).intersect(conflictingAttributes).nonEmpty =>
             (oldVersion, oldVersion.copy(aggregateExpressions = newAliases(aggregateExpressions)))
-        }.head // Only handle first case found, others will be fixed on the next pass.
+        }.headOption.getOrElse { // Only handle first case, others will be fixed on the next pass.
+          sys.error(
+            s"""
+              |Failure when resolving conflicting references in Join:
+              |$plan
+              |
+              |Conflicting attributes: ${conflictingAttributes.mkString(",")}
+              """.stripMargin)
+        }
 
         val attributeRewrites = AttributeMap(oldRelation.output.zip(newRelation.output))
         val newRight = right transformUp {
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/MultiInstanceRelation.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/MultiInstanceRelation.scala
index 894c3500cf..35b74024a4 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/MultiInstanceRelation.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/MultiInstanceRelation.scala
@@ -30,5 +30,5 @@ import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
  * of itself with globally unique expression ids.
  */
 trait MultiInstanceRelation {
-  def newInstance(): this.type
+  def newInstance(): LogicalPlan
 }