Fix v15 build (#90)

* Fix creation of the "custom_objects_cache" hash table

The hash table was declared as hashing strings, but is used for OIDs.
This bug was brought to light by PostgreSQL commit b3817f5f77, which
made it compulsory to specify the kind of objects that was hashed.

* Remove reference to the "Value" node

PostgreSQL commit 639a86e36a removed "Value", so use "Node" instead.

* Adapt to PostgreSQL commit a49d081235

That commit got rid of FirstBootstrapObjectId and
introduced FirstUnpinnedObjectId instead.

src/custom_types.c

@@ -43,7 +43,7 @@ create_custom_objects_cache(void)
 	ctl.keysize = sizeof(Oid);
 	ctl.entrysize = sizeof(CustomObjectDef);
 
-	return hash_create("clickhouse_fdw custom functions", 20, &ctl, HASH_ELEM);
+	return hash_create("clickhouse_fdw custom functions", 20, &ctl, HASH_ELEM | HASH_BLOBS);
 }
 
 static void

src/include/clickhousedb_fdw.h

@@ -25,6 +25,10 @@
 #include "nodes/pathnodes.h"
 #endif
 
+#if PG_VERSION_NUM < 150000
+#define FirstUnpinnedObjectId FirstBootstrapObjectId
+#endif
+
 /* libclickhouse_link.c */
 typedef struct ch_cursor ch_cursor;
 typedef struct ch_cursor

src/pglink.c

@@ -940,7 +940,7 @@ chfdw_construct_create_tables(ImportForeignSchemaStmt *stmt, ForeignServer *serv
 				appendStringInfoString(&buf, " OPTIONS (");
 				foreach(lc, options)
 				{
-					Value	*val = lfirst(lc);
+					Node	*val = lfirst(lc);
 					if (IsA(val, Integer))
 					{
 						if (!first)

src/shipable.c

@@ -134,7 +134,7 @@ lookup_shippable(Oid objectId, Oid classId, CHFdwRelationInfo *fpinfo)
 /*
  * Return true if given object is one of PostgreSQL's built-in objects.
  *
- * We use FirstBootstrapObjectId as the cutoff, so that we only consider
+ * We use FirstUnpinnedObjectId as the cutoff, so that we only consider
  * objects with hand-assigned OIDs to be "built in", not for instance any
  * function or type defined in the information_schema.
  *
@@ -151,7 +151,7 @@ lookup_shippable(Oid objectId, Oid classId, CHFdwRelationInfo *fpinfo)
 bool
 chfdw_is_builtin(Oid objectId)
 {
-	return (objectId < FirstBootstrapObjectId);
+	return (objectId < FirstUnpinnedObjectId);
 }
 
 /*