Fixed potential endless loop inside MET_scan_relation: when relation is system-defined and its ODS is greater than ODS of current database.

Thanks to @dyemanov for pointing into this.

Author: hvlad

src/jrd/met.epp

@@ -115,6 +115,7 @@ static int blocking_ast_relation(void*);
 static int partners_ast_relation(void*);
 static int rescan_ast_relation(void*);
 static ULONG get_rel_flags_from_FLAGS(USHORT);
+static USHORT get_sysrel_ods(jrd_rel*);
 static void get_trigger(thread_db*, jrd_rel*, bid*, bid*, TrigVector**, const TEXT*, FB_UINT64, SSHORT,
 	USHORT, const MetaName&, const string&, const bid*, Nullable<bool> ssDefiner);
 static bool get_type(thread_db*, USHORT*, const UCHAR*, const TEXT*);
@@ -4095,9 +4096,13 @@ static void scan_relation(thread_db* tdbb, jrd_rel* relation)
 	AutoCacheRequest request(tdbb, irq_r_fields, IRQ_REQUESTS);
 	CompilerScratch* csb = NULL;
 
+	bool found = false;
+
 	FOR(REQUEST_HANDLE request)
 		REL IN RDB$RELATIONS WITH REL.RDB$RELATION_ID EQ relation->rel_id
 	{
+		found = true;
+
 		// Pick up relation level stuff
 		relation->rel_current_fmt = REL.RDB$FORMAT;
 		vec<jrd_fld*>* vector = relation->rel_fields =
@@ -4371,6 +4376,30 @@ static void scan_relation(thread_db* tdbb, jrd_rel* relation)
 
 	delete csb;
 
+	if (!found && !(relation->rel_flags & REL_scanned))
+	{
+		// Relation was not found in RDB$RELATIONS. It could be system relation
+		// defined in INI for latest supported ODS while database is in older ODS.
+
+		const USHORT dbbOds = ENCODE_ODS(dbb->dbb_ods_version, dbb->dbb_minor_version);
+
+		if (relation->isSystem() && dbbOds < ODS_CURRENT_VERSION &&
+			dbbOds < get_sysrel_ods(relation))
+		{
+			relation->rel_flags |= REL_scanned;
+		}
+		else
+		{
+			fb_assert(false);
+
+			string name(relation->rel_name);
+			if (name.isEmpty())
+				name.printf("<ID = %u>", relation->rel_id);
+
+			ERR_post(Arg::Gds(isc_relnotdef) << Arg::Str(name));
+		}
+	}
+
 	// We have just loaded the triggers onto the local vector triggers.
 	// It's now time to place them at their rightful place inside the relation block.
 
@@ -4776,6 +4805,37 @@ ULONG MET_get_rel_flags_from_TYPE(USHORT type)
 }
 
 
+// Search system-defined list for given relation and return its ODS.
+// Return zero, if not found.
+static USHORT get_sysrel_ods(jrd_rel* relation)
+{
+	if (relation->rel_id >= rel_MAX)
+		return 0;
+
+#define RELATION(name, id, ods, type) id, ods,
+#define FIELD(symbol, name, id, update, ods)
+#define END_RELATION
+
+	static const int rels[] =
+	{
+	#include "../jrd/relations.h"
+		0, 0
+	};
+
+#undef RELATION
+#undef FIELD
+#undef END_RELATION
+
+	for (int n = 0; n < FB_NELEM(rels); n += 2)
+	{
+		if (relation->rel_id == rels[n])
+			return rels[n + 1];
+	}
+
+	return 0;
+}
+
+
 static void get_trigger(thread_db* tdbb, jrd_rel* relation,
 						bid* blob_id, bid* debug_blob_id, TrigVector** ptr,
 						const TEXT* name, FB_UINT64 type,