Rescue PGQuery::ParseError in prevent_cross_joins

This can happen for some valid Postgres queries due to an issue with the
library handling large nested queries. As such it's safest to just
ignore any queries that fail to parse.

spec/support/database/prevent_cross_joins.rb

@@ -31,9 +31,13 @@ module Database
       # See https://gitlab.com/gitlab-org/gitlab/-/issues/339396
       return if sql.include?("DISABLE TRIGGER") || sql.include?("ENABLE TRIGGER")
 
-      # PgQuery might fail in some cases due to limited nesting:
-      # https://github.com/pganalyze/pg_query/issues/209
-      tables = PgQuery.parse(sql).tables
+      tables = begin
+        PgQuery.parse(sql).tables
+      rescue PgQuery::ParseError
+        # PgQuery might fail in some cases due to limited nesting:
+        # https://github.com/pganalyze/pg_query/issues/209
+        return
+      end
 
       schemas = ::Gitlab::Database::GitlabSchema.table_schemas(tables)
 

spec/support_specs/database/prevent_cross_joins_spec.rb

@@ -39,6 +39,15 @@ RSpec.describe Database::PreventCrossJoins do
           expect { main_and_ci_query_allowlist_nested }.not_to raise_error
         end
       end
+
+      context 'when there is a parser error' do
+        it 'does not raise parse PGQuery::ParseError' do
+          # Since this is in an invalid query it still raises from ActiveRecord
+          # but this tests that we rescue the PGQuery::ParseError which would
+          # have otherwise raised first
+          expect { ApplicationRecord.connection.execute('SELECT SELECT FROM SELECT') }.to raise_error(ActiveRecord::StatementInvalid)
+        end
+      end
     end
   end