Handle INSERT .. ON CONFLICT with partitioned tables

Commit eb7ed3f306 enabled unique constraints on partitioned tables,
but one thing that was not working properly is INSERT/ON CONFLICT.
This commit introduces a new node keeps state related to the ON CONFLICT
clause per partition, and fills it when that partition is about to be
used for tuple routing.

Author: Amit Langote, Álvaro Herrera
Reviewed-by: Etsuro Fujita, Pavan Deolasee
Discussion: https://postgr.es/m/20180228004602.cwdyralmg5ejdqkq@alvherre.pgsql

src/include/nodes/execnodes.h

@@ -362,6 +362,20 @@ typedef struct JunkFilter
 	AttrNumber	jf_junkAttNo;
 } JunkFilter;
 
+/*
+ * OnConflictSetState
+ *
+ * Executor state of an ON CONFLICT DO UPDATE operation.
+ */
+typedef struct OnConflictSetState
+{
+	NodeTag		type;
+
+	ProjectionInfo *oc_ProjInfo;	/* for ON CONFLICT DO UPDATE SET */
+	TupleDesc	oc_ProjTupdesc; /* TupleDesc for the above projection */
+	ExprState  *oc_WhereClause; /* state for the WHERE clause */
+} OnConflictSetState;
+
 /*
  * ResultRelInfo
  *
@@ -424,11 +438,11 @@ typedef struct ResultRelInfo
 	/* for computing a RETURNING list */
 	ProjectionInfo *ri_projectReturning;
 
-	/* for computing ON CONFLICT DO UPDATE SET */
-	ProjectionInfo *ri_onConflictSetProj;
+	/* list of arbiter indexes to use to check conflicts */
+	List	   *ri_onConflictArbiterIndexes;
 
-	/* list of ON CONFLICT DO UPDATE exprs (qual) */
-	ExprState  *ri_onConflictSetWhere;
+	/* ON CONFLICT evaluation state */
+	OnConflictSetState *ri_onConflict;
 
 	/* partition check expression */
 	List	   *ri_PartitionCheck;

src/include/nodes/nodes.h

@@ -34,6 +34,7 @@ typedef enum NodeTag
 	T_ExprContext,
 	T_ProjectionInfo,
 	T_JunkFilter,
+	T_OnConflictSetState,
 	T_ResultRelInfo,
 	T_EState,
 	T_TupleTableSlot,