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

src/include/parser/analyze.h

@@ -23,7 +23,7 @@ extern PGDLLIMPORT post_parse_analyze_hook_type post_parse_analyze_hook;
 
 
 extern Query *parse_analyze(RawStmt *parseTree, const char *sourceText,
-			  Oid *paramTypes, int numParams);
+			  Oid *paramTypes, int numParams, QueryEnvironment *queryEnv);
 extern Query *parse_analyze_varparams(RawStmt *parseTree, const char *sourceText,
 						Oid **paramTypes, int *numParams);
 

src/include/parser/parse_enr.h

@@ -0,0 +1,22 @@
+/*-------------------------------------------------------------------------
+ *
+ * parse_enr.h
+ *		Internal definitions for parser
+ *
+ *
+ * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/parser/parse_enr.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PARSE_ENR_H
+#define PARSE_ENR_H
+
+#include "parser/parse_node.h"
+
+extern bool name_matches_visible_ENR(ParseState *pstate, const char *refname);
+extern EphemeralNamedRelationMetadata get_visible_ENR(ParseState *pstate, const char *refname);
+
+#endif   /* PARSE_ENR_H */

src/include/parser/parse_node.h

@@ -15,6 +15,7 @@
 #define PARSE_NODE_H
 
 #include "nodes/parsenodes.h"
+#include "utils/queryenvironment.h"
 #include "utils/relcache.h"
 
 
@@ -188,6 +189,8 @@ struct ParseState
 	bool		p_resolve_unknowns;		/* resolve unknown-type SELECT outputs
 										 * as type text */
 
+	QueryEnvironment *p_queryEnv; /* curr env, incl refs to enclosing env */
+
 	/* Flags telling about things found in the query: */
 	bool		p_hasAggs;
 	bool		p_hasWindowFuncs;

src/include/parser/parse_relation.h

@@ -42,6 +42,7 @@ extern RangeTblEntry *refnameRangeTblEntry(ParseState *pstate,
 extern CommonTableExpr *scanNameSpaceForCTE(ParseState *pstate,
 					const char *refname,
 					Index *ctelevelsup);
+extern bool scanNameSpaceForENR(ParseState *pstate, const char *refname);
 extern void checkNameSpaceConflicts(ParseState *pstate, List *namespace1,
 						List *namespace2);
 extern int RTERangeTablePosn(ParseState *pstate,
@@ -107,6 +108,9 @@ extern RangeTblEntry *addRangeTableEntryForCTE(ParseState *pstate,
 						 Index levelsup,
 						 RangeVar *rv,
 						 bool inFromCl);
+extern RangeTblEntry *addRangeTableEntryForENR(ParseState *pstate,
+						 RangeVar *rv,
+						 bool inFromCl);
 extern bool isLockedRefname(ParseState *pstate, const char *refname);
 extern void addRTEtoQuery(ParseState *pstate, RangeTblEntry *rte,
 			  bool addToJoinList,