fix(cassandra): list table triggers from system schema

Closes #6751

agents/drivers/cassandra-go/main.go

@@ -358,7 +358,8 @@ func (s *server) dispatch(method string, params map[string]json.RawMessage) (any
 	case "list_foreign_keys":
 		return []foreignKeyInfo{}, false, nil
 	case "list_triggers":
-		return []triggerInfo{}, false, nil
+		result, err := s.listTriggers(stringParam(params, "schema"), stringParam(params, "table"))
+		return result, false, err
 	case "get_object_source":
 		return nil, false, errors.New("object source is not supported by Cassandra")
 	case "get_table_ddl":

agents/drivers/cassandra-go/metadata.go

@@ -82,6 +82,15 @@ type triggerInfo struct {
 	Timing string `json:"timing"`
 }
 
+const cassandraListTriggersCQL = "SELECT trigger_name, options FROM system_schema.triggers WHERE keyspace_name = ? AND table_name = ?"
+
+type metadataIterator interface {
+	Scan(...any) bool
+	Close() error
+}
+
+type metadataQuery func(string, ...any) metadataIterator
+
 type metadataListConstraints struct {
 	Filter      string
 	Limit       int
@@ -321,6 +330,35 @@ func (s *server) querySystemIndexes(schema, table string) ([]indexInfo, error) {
 	return result, nil
 }
 
+func (s *server) listTriggers(schema, table string) ([]triggerInfo, error) {
+	session, err := s.runtime.sessionFor("")
+	if err != nil {
+		return nil, err
+	}
+	return listTriggersWithQuery(func(query string, values ...any) metadataIterator {
+		return session.Query(query, values...).Iter()
+	}, schema, table)
+}
+
+func listTriggersWithQuery(query metadataQuery, schema, table string) ([]triggerInfo, error) {
+	iter := query(cassandraListTriggersCQL, schema, table)
+	result := []triggerInfo{}
+	var name string
+	var options map[string]string
+	for iter.Scan(&name, &options) {
+		// Cassandra trigger metadata stores only the trigger class. Cassandra
+		// invokes every trigger before any DML statement, so expose those fixed
+		// semantics through the common TriggerInfo contract.
+		result = append(result, triggerInfo{Name: name, Event: "DML", Timing: "BEFORE"})
+		options = nil
+	}
+	if err := iter.Close(); err != nil {
+		return nil, err
+	}
+	sort.Slice(result, func(left, right int) bool { return result[left].Name < result[right].Name })
+	return result, nil
+}
+
 func mergeIndexes(first, second []indexInfo) []indexInfo {
 	byName := make(map[string]indexInfo, len(first)+len(second))
 	for _, index := range first {

agents/drivers/cassandra-go/metadata_test.go

@@ -1,12 +1,37 @@
 package main
 
 import (
+	"errors"
 	"reflect"
 	"testing"
 
 	gocql "github.com/apache/cassandra-gocql-driver/v2"
 )
 
+type triggerMetadataIterator struct {
+	rows []struct {
+		name    string
+		options map[string]string
+	}
+	index    int
+	closeErr error
+}
+
+func (i *triggerMetadataIterator) Scan(dest ...any) bool {
+	if i.index >= len(i.rows) {
+		return false
+	}
+	row := i.rows[i.index]
+	i.index++
+	*dest[0].(*string) = row.name
+	*dest[1].(*map[string]string) = row.options
+	return true
+}
+
+func (i *triggerMetadataIterator) Close() error {
+	return i.closeErr
+}
+
 func TestColumnsIndexesAndDDLFromMetadata(t *testing.T) {
 	textType := gocql.NewNativeType(4, gocql.TypeVarchar, "")
 	intType := gocql.NewNativeType(4, gocql.TypeInt, "")
@@ -84,3 +109,53 @@ func TestQuoteCQLIdentifierEscapesQuotes(t *testing.T) {
 		t.Fatalf("unexpected quoted identifier: %s", got)
 	}
 }
+
+func TestListTriggersQueriesExactTableAndMapsMetadata(t *testing.T) {
+	var statement string
+	var values []any
+	triggers, err := listTriggersWithQuery(func(query string, args ...any) metadataIterator {
+		statement = query
+		values = args
+		return &triggerMetadataIterator{rows: []struct {
+			name    string
+			options map[string]string
+		}{
+			{name: "capture_changes", options: map[string]string{"class": "example.CaptureDataTrigger"}},
+		}}
+	}, "dev", "example")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if statement != cassandraListTriggersCQL {
+		t.Fatalf("unexpected trigger query: %s", statement)
+	}
+	if !reflect.DeepEqual(values, []any{"dev", "example"}) {
+		t.Fatalf("trigger filters = %#v", values)
+	}
+	want := []triggerInfo{{Name: "capture_changes", Event: "DML", Timing: "BEFORE"}}
+	if !reflect.DeepEqual(triggers, want) {
+		t.Fatalf("triggers = %#v, want %#v", triggers, want)
+	}
+}
+
+func TestListTriggersReturnsEmptySlice(t *testing.T) {
+	triggers, err := listTriggersWithQuery(func(string, ...any) metadataIterator {
+		return &triggerMetadataIterator{}
+	}, "dev", "empty_table")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if triggers == nil || len(triggers) != 0 {
+		t.Fatalf("triggers = %#v, want a non-nil empty slice", triggers)
+	}
+}
+
+func TestListTriggersReturnsQueryError(t *testing.T) {
+	wantErr := errors.New("trigger metadata unavailable")
+	triggers, err := listTriggersWithQuery(func(string, ...any) metadataIterator {
+		return &triggerMetadataIterator{closeErr: wantErr}
+	}, "dev", "example")
+	if !errors.Is(err, wantErr) || triggers != nil {
+		t.Fatalf("triggers = %#v, err = %v", triggers, err)
+	}
+}