Add infrastructure to support EphemeralNamedRelation references.

A QueryEnvironment concept is added, which allows new types of
objects to be passed into queries from parsing on through
execution.  At this point, the only thing implemented is a
collection of EphemeralNamedRelation objects -- relations which
can be referenced by name in queries, but do not exist in the
catalogs.  The only type of ENR implemented is NamedTuplestore, but
provision is made to add more types fairly easily.

An ENR can carry its own TupleDesc or reference a relation in the
catalogs by relid.

Although these features can be used without SPI, convenience
functions are added to SPI so that ENRs can easily be used by code
run through SPI.

The initial use of all this is going to be transition tables in
AFTER triggers, but that will be added to each PL as a separate
commit.

An incidental effect of this patch is to produce a more informative
error message if an attempt is made to modify the contents of a CTE
from a referencing DML statement.  No tests previously covered that
possibility, so one is added.

Kevin Grittner and Thomas Munro
Reviewed by Heikki Linnakangas, David Fetter, and Thomas Munro
with valuable comments and suggestions from many others

4 files changed, 32 insertions, 4 deletions

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index a578867cced..59d71c1b320 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -4910,7 +4910,7 @@ inline_set_returning_function(PlannerInfo *root, RangeTblEntry *rte)
 	querytree_list = pg_analyze_and_rewrite_params(linitial(raw_parsetree_list),
 												   src,
 									   (ParserSetupHook) sql_fn_parser_setup,
-												   pinfo);
+												   pinfo, NULL);
 	if (list_length(querytree_list) != 1)
 		goto fail;
 	querytree = linitial(querytree_list);
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index c6298072c9b..85362121774 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -1893,6 +1893,32 @@ create_ctescan_path(PlannerInfo *root, RelOptInfo *rel, Relids required_outer)
 }
 
 /*
+ * create_namedtuplestorescan_path
+ *	  Creates a path corresponding to a scan of a named tuplestore, returning
+ *	  the pathnode.
+ */
+Path *
+create_namedtuplestorescan_path(PlannerInfo *root, RelOptInfo *rel,
+								Relids required_outer)
+{
+	Path	   *pathnode = makeNode(Path);
+
+	pathnode->pathtype = T_NamedTuplestoreScan;
+	pathnode->parent = rel;
+	pathnode->pathtarget = rel->reltarget;
+	pathnode->param_info = get_baserel_parampathinfo(root, rel,
+													 required_outer);
+	pathnode->parallel_aware = false;
+	pathnode->parallel_safe = rel->consider_parallel;
+	pathnode->parallel_workers = 0;
+	pathnode->pathkeys = NIL;	/* result is always unordered */
+
+	cost_namedtuplestorescan(pathnode, root, rel, pathnode->param_info);
+
+	return pathnode;
+}
+
+/*
  * create_worktablescan_path
  *	  Creates a path corresponding to a scan of a self-reference CTE,
  *	  returning the pathnode.
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index cc88dcc28e4..1cd21c0fdcb 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -1446,9 +1446,9 @@ relation_excluded_by_constraints(PlannerInfo *root,
  * dropped cols.
  *
  * We also support building a "physical" tlist for subqueries, functions,
- * values lists, table expressions and CTEs, since the same optimization can
- * occur in SubqueryScan, FunctionScan, ValuesScan, CteScan, TableFunc
- * and WorkTableScan nodes.
+ * values lists, table expressions, and CTEs, since the same optimization can
+ * occur in SubqueryScan, FunctionScan, ValuesScan, CteScan, TableFunc,
+ * NamedTuplestoreScan, and WorkTableScan nodes.
  */
 List *
 build_physical_tlist(PlannerInfo *root, RelOptInfo *rel)
@@ -1523,6 +1523,7 @@ build_physical_tlist(PlannerInfo *root, RelOptInfo *rel)
 		case RTE_TABLEFUNC:
 		case RTE_VALUES:
 		case RTE_CTE:
+		case RTE_NAMEDTUPLESTORE:
 			/* Not all of these can have dropped cols, but share code anyway */
 			expandRTE(rte, varno, 0, -1, true /* include dropped */ ,
 					  NULL, &colvars);
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 6ab78545c36..7912df0baaa 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -156,6 +156,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
 		case RTE_TABLEFUNC:
 		case RTE_VALUES:
 		case RTE_CTE:
+		case RTE_NAMEDTUPLESTORE:
 
 			/*
 			 * Subquery, function, tablefunc, or values list --- set up attr