feat(librarian/swift): default output directory

internal/librarian/generate.go

@@ -269,6 +269,8 @@ func defaultOutput(language string, name, api, defaultOut string) string {
 		return python.DefaultOutput(name, defaultOut)
 	case config.LanguageRust:
 		return rust.DefaultOutput(api, defaultOut)
+	case config.LanguageSwift:
+		return swift.DefaultOutput(api, defaultOut)	
 	default:
 		return defaultOut
 	}

internal/librarian/swift/default_output.go

@@ -0,0 +1,24 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package swift
+
+import "path/filepath"
+
+// DefaultOutput derives an output path from a library name and a default
+// output directory. Currently, this just assumes each library is a directory
+// directly underneath the default output directory.
+func DefaultOutput(name, defaultOutput string) string {
+	return filepath.Join(defaultOutput, name)
+}

internal/librarian/swift/default_output_test.go

@@ -0,0 +1,54 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package swift
+
+import "testing"
+
+func TestDefaultOutput(t *testing.T) {
+	tests := []struct {
+		name    string
+		libName string
+		defOut  string
+		want    string
+	}{
+		{
+			name:    "simple",
+			libName: "secretmanager",
+			defOut:  "packages",
+			want:    "packages/secretmanager",
+		},
+		{
+			name:    "empty default",
+			libName: "secretmanager",
+			defOut:  "",
+			want:    "secretmanager",
+		},
+		{
+			name:    "nested default",
+			libName: "secretmanager",
+			defOut:  "a/b/c",
+			want:    "a/b/c/secretmanager",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := DefaultOutput(tt.libName, tt.defOut)
+			if got != tt.want {
+				t.Errorf("DefaultOutput(%q, %q) = %q; want %q", tt.libName, tt.defOut, got, tt.want)
+			}
+		})
+	}
+}