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, 35 insertions, 11 deletions

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index c762fb07d4d..ee7046c47b9 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -53,7 +53,8 @@ explain_get_index_name_hook_type explain_get_index_name_hook = NULL;
 #define X_CLOSE_IMMEDIATE 2
 #define X_NOWHITESPACE 4
 
-static void ExplainOneQuery(Query *query, IntoClause *into, ExplainState *es,
+static void ExplainOneQuery(Query *query, int cursorOptions,
+				IntoClause *into, ExplainState *es,
 				const char *queryString, ParamListInfo params);
 static void report_triggers(ResultRelInfo *rInfo, bool show_relname,
 				ExplainState *es);
@@ -245,7 +246,8 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt, const char *queryString,
 		/* Explain every plan */
 		foreach(l, rewritten)
 		{
-			ExplainOneQuery((Query *) lfirst(l), NULL, es,
+			ExplainOneQuery((Query *) lfirst(l),
+							CURSOR_OPT_PARALLEL_OK, NULL, es,
 							queryString, params);
 
 			/* Separate plans with an appropriate separator */
@@ -329,7 +331,8 @@ ExplainResultDesc(ExplainStmt *stmt)
  * "into" is NULL unless we are explaining the contents of a CreateTableAsStmt.
  */
 static void
-ExplainOneQuery(Query *query, IntoClause *into, ExplainState *es,
+ExplainOneQuery(Query *query, int cursorOptions,
+				IntoClause *into, ExplainState *es,
 				const char *queryString, ParamListInfo params)
 {
 	/* planner will not cope with utility statements */
@@ -341,7 +344,8 @@ ExplainOneQuery(Query *query, IntoClause *into, ExplainState *es,
 
 	/* if an advisor plugin is present, let it manage things */
 	if (ExplainOneQuery_hook)
-		(*ExplainOneQuery_hook) (query, into, es, queryString, params);
+		(*ExplainOneQuery_hook) (query, cursorOptions, into, es,
+								 queryString, params);
 	else
 	{
 		PlannedStmt *plan;
@@ -351,7 +355,7 @@ ExplainOneQuery(Query *query, IntoClause *into, ExplainState *es,
 		INSTR_TIME_SET_CURRENT(planstart);
 
 		/* plan the query */
-		plan = pg_plan_query(query, into ? 0 : CURSOR_OPT_PARALLEL_OK, params);
+		plan = pg_plan_query(query, cursorOptions, params);
 
 		INSTR_TIME_SET_CURRENT(planduration);
 		INSTR_TIME_SUBTRACT(planduration, planstart);
@@ -385,6 +389,8 @@ ExplainOneUtility(Node *utilityStmt, IntoClause *into, ExplainState *es,
 		 * We have to rewrite the contained SELECT and then pass it back to
 		 * ExplainOneQuery.  It's probably not really necessary to copy the
 		 * contained parsetree another time, but let's be safe.
+		 *
+		 * Like ExecCreateTableAs, disallow parallelism in the plan.
 		 */
 		CreateTableAsStmt *ctas = (CreateTableAsStmt *) utilityStmt;
 		List	   *rewritten;
@@ -392,7 +398,28 @@ ExplainOneUtility(Node *utilityStmt, IntoClause *into, ExplainState *es,
 		Assert(IsA(ctas->query, Query));
 		rewritten = QueryRewrite((Query *) copyObject(ctas->query));
 		Assert(list_length(rewritten) == 1);
-		ExplainOneQuery((Query *) linitial(rewritten), ctas->into, es,
+		ExplainOneQuery((Query *) linitial(rewritten),
+						0, ctas->into, es,
+						queryString, params);
+	}
+	else if (IsA(utilityStmt, DeclareCursorStmt))
+	{
+		/*
+		 * Likewise for DECLARE CURSOR.
+		 *
+		 * Notice that if you say EXPLAIN ANALYZE DECLARE CURSOR then we'll
+		 * actually run the query.  This is different from pre-8.3 behavior
+		 * but seems more useful than not running the query.  No cursor will
+		 * be created, however.
+		 */
+		DeclareCursorStmt *dcs = (DeclareCursorStmt *) utilityStmt;
+		List	   *rewritten;
+
+		Assert(IsA(dcs->query, Query));
+		rewritten = QueryRewrite((Query *) copyObject(dcs->query));
+		Assert(list_length(rewritten) == 1);
+		ExplainOneQuery((Query *) linitial(rewritten),
+						dcs->options, NULL, es,
 						queryString, params);
 	}
 	else if (IsA(utilityStmt, ExecuteStmt))
@@ -423,11 +450,6 @@ ExplainOneUtility(Node *utilityStmt, IntoClause *into, ExplainState *es,
  * "into" is NULL unless we are explaining the contents of a CreateTableAsStmt,
  * in which case executing the query should result in creating that table.
  *
- * Since we ignore any DeclareCursorStmt that might be attached to the query,
- * if you say EXPLAIN ANALYZE DECLARE CURSOR then we'll actually run the
- * query.  This is different from pre-8.3 behavior but seems more useful than
- * not running the query.  No cursor will be created, however.
- *
  * This is exported because it's called back from prepare.c in the
  * EXPLAIN EXECUTE case, and because an index advisor plugin would need
  * to call it.
@@ -444,6 +466,8 @@ ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
 	int			eflags;
 	int			instrument_option = 0;
 
+	Assert(plannedstmt->commandType != CMD_UTILITY);
+
 	if (es->analyze && es->timing)
 		instrument_option |= INSTRUMENT_TIMER;
 	else if (es->analyze)