Ensure that expandTableLikeClause() re-examines the same table.

As it stood, expandTableLikeClause() re-did the same relation_openrv
call that transformTableLikeClause() had done.  However there are
scenarios where this would not find the same table as expected.
We hold lock on the LIKE source table, so it can't be renamed or
dropped, but another table could appear before it in the search path.
This explains the odd behavior reported in bug #16758 when cloning a
table as a temp table of the same name.  This case worked as expected
before commit 50289819 introduced the need to open the source table
twice, so we should fix it.

To make really sure we get the same table, let's re-open it by OID not
name.  That requires adding an OID field to struct TableLikeClause,
which is a little nervous-making from an ABI standpoint, but as long
as it's at the end I don't think there's any serious risk.

Per bug #16758 from Marc Boeren.  Like the previous patch,
back-patch to all supported branches.

Discussion: https://postgr.es/m/16758-840e84a6cfab276d@postgresql.org

src/backend/nodes/copyfuncs.c

@@ -3411,6 +3411,7 @@ _copyTableLikeClause(const TableLikeClause *from)
 
 	COPY_NODE_FIELD(relation);
 	COPY_SCALAR_FIELD(options);
+	COPY_SCALAR_FIELD(relationOid);
 
 	return newnode;
 }

src/backend/nodes/equalfuncs.c

@@ -1254,6 +1254,7 @@ _equalTableLikeClause(const TableLikeClause *a, const TableLikeClause *b)
 {
 	COMPARE_NODE_FIELD(relation);
 	COMPARE_SCALAR_FIELD(options);
+	COMPARE_SCALAR_FIELD(relationOid);
 
 	return true;
 }

src/backend/nodes/outfuncs.c

@@ -2811,6 +2811,7 @@ _outTableLikeClause(StringInfo str, const TableLikeClause *node)
 
 	WRITE_NODE_FIELD(relation);
 	WRITE_UINT_FIELD(options);
+	WRITE_OID_FIELD(relationOid);
 }
 
 static void

src/backend/parser/gram.y

@@ -3643,6 +3643,7 @@ TableLikeClause:
 					TableLikeClause *n = makeNode(TableLikeClause);
 					n->relation = $2;
 					n->options = $3;
+					n->relationOid = InvalidOid;
 					$$ = (Node *)n;
 				}
 		;

src/backend/parser/parse_utilcmd.c

@@ -1105,14 +1105,18 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
 	 * we don't yet know what column numbers the copied columns will have in
 	 * the finished table.  If any of those options are specified, add the
 	 * LIKE clause to cxt->likeclauses so that expandTableLikeClause will be
-	 * called after we do know that.
+	 * called after we do know that.  Also, remember the relation OID so that
+	 * expandTableLikeClause is certain to open the same table.
 	 */
 	if (table_like_clause->options &
 		(CREATE_TABLE_LIKE_DEFAULTS |
 		 CREATE_TABLE_LIKE_GENERATED |
 		 CREATE_TABLE_LIKE_CONSTRAINTS |
 		 CREATE_TABLE_LIKE_INDEXES))
+	{
+		table_like_clause->relationOid = RelationGetRelid(relation);
 		cxt->likeclauses = lappend(cxt->likeclauses, table_like_clause);
+	}
 
 	/*
 	 * We may copy extended statistics if requested, since the representation
@@ -1185,9 +1189,13 @@ expandTableLikeClause(RangeVar *heapRel, TableLikeClause *table_like_clause)
 	 * Open the relation referenced by the LIKE clause.  We should still have
 	 * the table lock obtained by transformTableLikeClause (and this'll throw
 	 * an assertion failure if not).  Hence, no need to recheck privileges
-	 * etc.
+	 * etc.  We must open the rel by OID not name, to be sure we get the same
+	 * table.
 	 */
-	relation = relation_openrv(table_like_clause->relation, NoLock);
+	if (!OidIsValid(table_like_clause->relationOid))
+		elog(ERROR, "expandTableLikeClause called on untransformed LIKE clause");
+
+	relation = relation_open(table_like_clause->relationOid, NoLock);
 
 	tupleDesc = RelationGetDescr(relation);
 	constr = tupleDesc->constr;

src/include/nodes/parsenodes.h

@@ -673,6 +673,7 @@ typedef struct TableLikeClause
 	NodeTag		type;
 	RangeVar   *relation;
 	bits32		options;		/* OR of TableLikeOption flags */
+	Oid			relationOid;	/* If table has been looked up, its OID */
 } TableLikeClause;
 
 typedef enum TableLikeOption

src/test/regress/expected/create_table_like.out

@@ -455,6 +455,27 @@ Statistics objects:
     "public"."pg_attrdef_a_b_stat" (ndistinct, dependencies, mcv) ON a, b FROM public.pg_attrdef
 
 DROP TABLE public.pg_attrdef;
+-- Check that LIKE isn't confused when new table masks the old, either
+BEGIN;
+CREATE SCHEMA ctl_schema;
+SET LOCAL search_path = ctl_schema, public;
+CREATE TABLE ctlt1 (LIKE ctlt1 INCLUDING ALL);
+\d+ ctlt1
+                                Table "ctl_schema.ctlt1"
+ Column | Type | Collation | Nullable | Default | Storage  | Stats target | Description 
+--------+------+-----------+----------+---------+----------+--------------+-------------
+ a      | text |           | not null |         | main     |              | A
+ b      | text |           |          |         | extended |              | B
+Indexes:
+    "ctlt1_pkey" PRIMARY KEY, btree (a)
+    "ctlt1_b_idx" btree (b)
+    "ctlt1_expr_idx" btree ((a || b))
+Check constraints:
+    "ctlt1_a_check" CHECK (length(a) > 2)
+Statistics objects:
+    "ctl_schema"."ctlt1_a_b_stat" (ndistinct, dependencies, mcv) ON a, b FROM ctlt1
+
+ROLLBACK;
 DROP TABLE ctlt1, ctlt2, ctlt3, ctlt4, ctlt12_storage, ctlt12_comments, ctlt1_inh, ctlt13_inh, ctlt13_like, ctlt_all, ctla, ctlb CASCADE;
 NOTICE:  drop cascades to table inhe
 -- LIKE must respect NO INHERIT property of constraints

src/test/regress/sql/create_table_like.sql

@@ -173,6 +173,14 @@ CREATE TABLE pg_attrdef (LIKE ctlt1 INCLUDING ALL);
 \d+ public.pg_attrdef
 DROP TABLE public.pg_attrdef;
 
+-- Check that LIKE isn't confused when new table masks the old, either
+BEGIN;
+CREATE SCHEMA ctl_schema;
+SET LOCAL search_path = ctl_schema, public;
+CREATE TABLE ctlt1 (LIKE ctlt1 INCLUDING ALL);
+\d+ ctlt1
+ROLLBACK;
+
 DROP TABLE ctlt1, ctlt2, ctlt3, ctlt4, ctlt12_storage, ctlt12_comments, ctlt1_inh, ctlt13_inh, ctlt13_like, ctlt_all, ctla, ctlb CASCADE;
 
 -- LIKE must respect NO INHERIT property of constraints