Change representation of statement lists, and add statement location info.

This patch makes several changes that improve the consistency of
representation of lists of statements.  It's always been the case
that the output of parse analysis is a list of Query nodes, whatever
the types of the individual statements in the list.  This patch brings
similar consistency to the outputs of raw parsing and planning steps:

* The output of raw parsing is now always a list of RawStmt nodes;
the statement-type-dependent nodes are one level down from that.

* The output of pg_plan_queries() is now always a list of PlannedStmt
nodes, even for utility statements.  In the case of a utility statement,
"planning" just consists of wrapping a CMD_UTILITY PlannedStmt around
the utility node.  This list representation is now used in Portal and
CachedPlan plan lists, replacing the former convention of intermixing
PlannedStmts with bare utility-statement nodes.

Now, every list of statements has a consistent head-node type depending
on how far along it is in processing.  This allows changing many places
that formerly used generic "Node *" pointers to use a more specific
pointer type, thus reducing the number of IsA() tests and casts needed,
as well as improving code clarity.

Also, the post-parse-analysis representation of DECLARE CURSOR is changed
so that it looks more like EXPLAIN, PREPARE, etc.  That is, the contained
SELECT remains a child of the DeclareCursorStmt rather than getting flipped
around to be the other way.  It's now true for both Query and PlannedStmt
that utilityStmt is non-null if and only if commandType is CMD_UTILITY.
That allows simplifying a lot of places that were testing both fields.
(I think some of those were just defensive programming, but in many places,
it was actually necessary to avoid confusing DECLARE CURSOR with SELECT.)

Because PlannedStmt carries a canSetTag field, we're also able to get rid
of some ad-hoc rules about how to reconstruct canSetTag for a bare utility
statement; specifically, the assumption that a utility is canSetTag if and
only if it's the only one in its list.  While I see no near-term need for
relaxing that restriction, it's nice to get rid of the ad-hocery.

The API of ProcessUtility() is changed so that what it's passed is the
wrapper PlannedStmt not just the bare utility statement.  This will affect
all users of ProcessUtility_hook, but the changes are pretty trivial; see
the affected contrib modules for examples of the minimum change needed.
(Most compilers should give pointer-type-mismatch warnings for uncorrected
code.)

There's also a change in the API of ExplainOneQuery_hook, to pass through
cursorOptions instead of expecting hook functions to know what to pick.
This is needed because of the DECLARE CURSOR changes, but really should
have been done in 9.6; it's unlikely that any extant hook functions
know about using CURSOR_OPT_PARALLEL_OK.

Finally, teach gram.y to save statement boundary locations in RawStmt
nodes, and pass those through to Query and PlannedStmt nodes.  This allows
more intelligent handling of cases where a source query string contains
multiple statements.  This patch doesn't actually do anything with the
information, but a follow-on patch will.  (Passing this information through
cleanly is the true motivation for these changes; while I think this is all
good cleanup, it's unlikely we'd have bothered without this end goal.)

catversion bump because addition of location fields to struct Query
affects stored rules.

This patch is by me, but it owes a good deal to Fabien Coelho who did
a lot of preliminary work on the problem, and also reviewed the patch.

Discussion: https://postgr.es/m/alpine.DEB.2.20.1612200926310.29821@lancre

1 files changed, 42 insertions, 18 deletions

diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
index e48a878dc2a..c31c603fbf5 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -77,7 +77,7 @@
  */
 #define IsTransactionStmtPlan(plansource)  \
 	((plansource)->raw_parse_tree && \
-	 IsA((plansource)->raw_parse_tree, TransactionStmt))
+	 IsA((plansource)->raw_parse_tree->stmt, TransactionStmt))
 
 /*
  * This is the head of the backend's list of "saved" CachedPlanSources (i.e.,
@@ -95,6 +95,7 @@ static CachedPlan *BuildCachedPlan(CachedPlanSource *plansource, List *qlist,
 static bool choose_custom_plan(CachedPlanSource *plansource,
 				   ParamListInfo boundParams);
 static double cached_plan_cost(CachedPlan *plan, bool include_planner);
+static Query *QueryListGetPrimaryStmt(List *stmts);
 static void AcquireExecutorLocks(List *stmt_list, bool acquire);
 static void AcquirePlannerLocks(List *stmt_list, bool acquire);
 static void ScanQueryForLocks(Query *parsetree, bool acquire);
@@ -147,7 +148,7 @@ InitPlanCache(void)
  * commandTag: compile-time-constant tag for query, or NULL if empty query
  */
 CachedPlanSource *
-CreateCachedPlan(Node *raw_parse_tree,
+CreateCachedPlan(RawStmt *raw_parse_tree,
 				 const char *query_string,
 				 const char *commandTag)
 {
@@ -230,7 +231,7 @@ CreateCachedPlan(Node *raw_parse_tree,
  * commandTag: compile-time-constant tag for query, or NULL if empty query
  */
 CachedPlanSource *
-CreateOneShotCachedPlan(Node *raw_parse_tree,
+CreateOneShotCachedPlan(RawStmt *raw_parse_tree,
 						const char *query_string,
 						const char *commandTag)
 {
@@ -555,7 +556,7 @@ static List *
 RevalidateCachedQuery(CachedPlanSource *plansource)
 {
 	bool		snapshot_set;
-	Node	   *rawtree;
+	RawStmt    *rawtree;
 	List	   *tlist;			/* transient query-tree list */
 	List	   *qlist;			/* permanent query-tree list */
 	TupleDesc	resultDesc;
@@ -976,7 +977,7 @@ BuildCachedPlan(CachedPlanSource *plansource, List *qlist,
 	{
 		PlannedStmt *plannedstmt = (PlannedStmt *) lfirst(lc);
 
-		if (!IsA(plannedstmt, PlannedStmt))
+		if (plannedstmt->commandType == CMD_UTILITY)
 			continue;			/* Ignore utility statements */
 
 		if (plannedstmt->transientPlan)
@@ -1071,7 +1072,7 @@ cached_plan_cost(CachedPlan *plan, bool include_planner)
 	{
 		PlannedStmt *plannedstmt = (PlannedStmt *) lfirst(lc);
 
-		if (!IsA(plannedstmt, PlannedStmt))
+		if (plannedstmt->commandType == CMD_UTILITY)
 			continue;			/* Ignore utility statements */
 
 		result += plannedstmt->planTree->total_cost;
@@ -1419,7 +1420,7 @@ CachedPlanIsValid(CachedPlanSource *plansource)
 List *
 CachedPlanGetTargetList(CachedPlanSource *plansource)
 {
-	Node	   *pstmt;
+	Query	   *pstmt;
 
 	/* Assert caller is doing things in a sane order */
 	Assert(plansource->magic == CACHEDPLANSOURCE_MAGIC);
@@ -1436,9 +1437,34 @@ CachedPlanGetTargetList(CachedPlanSource *plansource)
 	RevalidateCachedQuery(plansource);
 
 	/* Get the primary statement and find out what it returns */
-	pstmt = PortalListGetPrimaryStmt(plansource->query_list);
+	pstmt = QueryListGetPrimaryStmt(plansource->query_list);
 
-	return FetchStatementTargetList(pstmt);
+	return FetchStatementTargetList((Node *) pstmt);
+}
+
+/*
+ * QueryListGetPrimaryStmt
+ *		Get the "primary" stmt within a list, ie, the one marked canSetTag.
+ *
+ * Returns NULL if no such stmt.  If multiple queries within the list are
+ * marked canSetTag, returns the first one.  Neither of these cases should
+ * occur in present usages of this function.
+ */
+static Query *
+QueryListGetPrimaryStmt(List *stmts)
+{
+	ListCell   *lc;
+
+	foreach(lc, stmts)
+	{
+		Query	   *stmt = (Query *) lfirst(lc);
+
+		Assert(IsA(stmt, Query));
+
+		if (stmt->canSetTag)
+			return stmt;
+	}
+	return NULL;
 }
 
 /*
@@ -1456,8 +1482,9 @@ AcquireExecutorLocks(List *stmt_list, bool acquire)
 		int			rt_index;
 		ListCell   *lc2;
 
-		Assert(!IsA(plannedstmt, Query));
-		if (!IsA(plannedstmt, PlannedStmt))
+		Assert(IsA(plannedstmt, PlannedStmt));
+
+		if (plannedstmt->commandType == CMD_UTILITY)
 		{
 			/*
 			 * Ignore utility statements, except those (such as EXPLAIN) that
@@ -1466,7 +1493,7 @@ AcquireExecutorLocks(List *stmt_list, bool acquire)
 			 * rule rewriting, because rewriting doesn't change the query
 			 * representation.
 			 */
-			Query	   *query = UtilityContainsQuery((Node *) plannedstmt);
+			Query	   *query = UtilityContainsQuery(plannedstmt->utilityStmt);
 
 			if (query)
 				ScanQueryForLocks(query, acquire);
@@ -1654,8 +1681,7 @@ PlanCacheComputeResultDesc(List *stmt_list)
 			return ExecCleanTypeFromTL(query->targetList, false);
 
 		case PORTAL_ONE_RETURNING:
-			query = (Query *) PortalListGetPrimaryStmt(stmt_list);
-			Assert(IsA(query, Query));
+			query = QueryListGetPrimaryStmt(stmt_list);
 			Assert(query->returningList);
 			return ExecCleanTypeFromTL(query->returningList, false);
 
@@ -1720,8 +1746,7 @@ PlanCacheRelCallback(Datum arg, Oid relid)
 			{
 				PlannedStmt *plannedstmt = (PlannedStmt *) lfirst(lc);
 
-				Assert(!IsA(plannedstmt, Query));
-				if (!IsA(plannedstmt, PlannedStmt))
+				if (plannedstmt->commandType == CMD_UTILITY)
 					continue;	/* Ignore utility statements */
 				if ((relid == InvalidOid) ? plannedstmt->relationOids != NIL :
 					list_member_oid(plannedstmt->relationOids, relid))
@@ -1795,8 +1820,7 @@ PlanCacheFuncCallback(Datum arg, int cacheid, uint32 hashvalue)
 				PlannedStmt *plannedstmt = (PlannedStmt *) lfirst(lc);
 				ListCell   *lc3;
 
-				Assert(!IsA(plannedstmt, Query));
-				if (!IsA(plannedstmt, PlannedStmt))
+				if (plannedstmt->commandType == CMD_UTILITY)
 					continue;	/* Ignore utility statements */
 				foreach(lc3, plannedstmt->invalItems)
 				{