Improve error reporting for tuple-routing failures.

Currently, the whole row is shown without column names.  Instead,
adopt a style similar to _bt_check_unique() in ExecFindPartition()
and show the failing key: (key1, ...) = (val1, ...).

Amit Langote, per a complaint from Simon Riggs.  Reviewed by me;
I also adjusted the grammar in one of the comments.

Discussion: http://postgr.es/m/9f9dc7ae-14f0-4a25-5485-964d9bfc19bd@lab.ntt.co.jp

src/backend/executor/execMain.c

@@ -60,6 +60,7 @@
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/rls.h"
+#include "utils/ruleutils.h"
 #include "utils/snapmgr.h"
 #include "utils/tqual.h"
 
@@ -95,6 +96,10 @@ static char *ExecBuildSlotValueDescription(Oid reloid,
 							  TupleDesc tupdesc,
 							  Bitmapset *modifiedCols,
 							  int maxfieldlen);
+static char *ExecBuildSlotPartitionKeyDescription(Relation rel,
+									 Datum *values,
+									 bool *isnull,
+									 int maxfieldlen);
 static void EvalPlanQualStart(EPQState *epqstate, EState *parentestate,
 				  Plan *planTree);
 
@@ -3189,33 +3194,122 @@ ExecFindPartition(ResultRelInfo *resultRelInfo, PartitionDispatch *pd,
 				  TupleTableSlot *slot, EState *estate)
 {
 	int			result;
-	Oid			failed_at;
+	PartitionDispatchData *failed_at;
+	TupleTableSlot *failed_slot;
 
-	result = get_partition_for_tuple(pd, slot, estate, &failed_at);
+	result = get_partition_for_tuple(pd, slot, estate,
+									 &failed_at, &failed_slot);
 	if (result < 0)
 	{
-		Relation	rel = resultRelInfo->ri_RelationDesc;
+		Relation	failed_rel;
+		Datum		key_values[PARTITION_MAX_KEYS];
+		bool		key_isnull[PARTITION_MAX_KEYS];
 		char	   *val_desc;
-		Bitmapset  *insertedCols,
-				   *updatedCols,
-				   *modifiedCols;
-		TupleDesc	tupDesc = RelationGetDescr(rel);
+		ExprContext *ecxt = GetPerTupleExprContext(estate);
 
-		insertedCols = GetInsertedColumns(resultRelInfo, estate);
-		updatedCols = GetUpdatedColumns(resultRelInfo, estate);
-		modifiedCols = bms_union(insertedCols, updatedCols);
-		val_desc = ExecBuildSlotValueDescription(RelationGetRelid(rel),
-												 slot,
-												 tupDesc,
-												 modifiedCols,
-												 64);
-		Assert(OidIsValid(failed_at));
+		failed_rel = failed_at->reldesc;
+		ecxt->ecxt_scantuple = failed_slot;
+		FormPartitionKeyDatum(failed_at, failed_slot, estate,
+							  key_values, key_isnull);
+		val_desc = ExecBuildSlotPartitionKeyDescription(failed_rel,
+														key_values,
+														key_isnull,
+														64);
+		Assert(OidIsValid(RelationGetRelid(failed_rel)));
 		ereport(ERROR,
 				(errcode(ERRCODE_CHECK_VIOLATION),
 				 errmsg("no partition of relation \"%s\" found for row",
-						get_rel_name(failed_at)),
-			val_desc ? errdetail("Failing row contains %s.", val_desc) : 0));
+						RelationGetRelationName(failed_rel)),
+			val_desc ? errdetail("Partition key of the failing row contains %s.", val_desc) : 0));
 	}
 
 	return result;
 }
+
+/*
+ * BuildSlotPartitionKeyDescription
+ *
+ * This works very much like BuildIndexValueDescription() and is currently
+ * used for building error messages when ExecFindPartition() fails to find
+ * partition for a row.
+ */
+static char *
+ExecBuildSlotPartitionKeyDescription(Relation rel,
+									 Datum *values,
+									 bool *isnull,
+									 int maxfieldlen)
+{
+	StringInfoData	buf;
+	PartitionKey	key = RelationGetPartitionKey(rel);
+	int			partnatts = get_partition_natts(key);
+	int			i;
+	Oid			relid = RelationGetRelid(rel);
+	AclResult	aclresult;
+
+	if (check_enable_rls(relid, InvalidOid, true) == RLS_ENABLED)
+		return NULL;
+
+	/* If the user has table-level access, just go build the description. */
+	aclresult = pg_class_aclcheck(relid, GetUserId(), ACL_SELECT);
+	if (aclresult != ACLCHECK_OK)
+	{
+		/*
+		 * Step through the columns of the partition key and make sure the
+		 * user has SELECT rights on all of them.
+		 */
+		for (i = 0; i < partnatts; i++)
+		{
+			AttrNumber	attnum = get_partition_col_attnum(key, i);
+
+			/*
+			 * If this partition key column is an expression, we return no
+			 * detail rather than try to figure out what column(s) the
+			 * expression includes and if the user has SELECT rights on them.
+			 */
+			if (attnum == InvalidAttrNumber ||
+				pg_attribute_aclcheck(relid, attnum, GetUserId(),
+									  ACL_SELECT) != ACLCHECK_OK)
+				return NULL;
+		}
+	}
+
+	initStringInfo(&buf);
+	appendStringInfo(&buf, "(%s) = (",
+					 pg_get_partkeydef_columns(relid, true));
+
+	for (i = 0; i < partnatts; i++)
+	{
+		char	   *val;
+		int			vallen;
+
+		if (isnull[i])
+			val = "null";
+		else
+		{
+			Oid			foutoid;
+			bool		typisvarlena;
+
+			getTypeOutputInfo(get_partition_col_typid(key, i),
+							  &foutoid, &typisvarlena);
+			val = OidOutputFunctionCall(foutoid, values[i]);
+		}
+
+		if (i > 0)
+			appendStringInfoString(&buf, ", ");
+
+		/* truncate if needed */
+		vallen = strlen(val);
+		if (vallen <= maxfieldlen)
+			appendStringInfoString(&buf, val);
+		else
+		{
+			vallen = pg_mbcliplen(val, vallen, maxfieldlen);
+			appendBinaryStringInfo(&buf, val, vallen);
+			appendStringInfoString(&buf, "...");
+		}
+	}
+
+	appendStringInfoChar(&buf, ')');
+
+	return buf.data;
+}