Derive selected overlay context from the main input

facade_main_relative_test.go

@@ -156,3 +156,65 @@ func TestMainRelativeWithoutBaseImportDefaults(t *testing.T) {
 		})
 	}
 }
+
+func TestLayeredOverlayContextSelection(t *testing.T) {
+	root := t.TempDir()
+	base := filepath.Join(root, "base")
+	for _, dir := range []string{filepath.Join(root, "overlays"), filepath.Join(base, "overlays")} {
+		if err := os.MkdirAll(dir, 0700); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for path, content := range map[string]string{"base/main.yml": "count: 1\n", "base/overlays/test.yml": "count: 2\n", "overlays/test.yml": "count: 3\n"} {
+		if err := os.WriteFile(filepath.Join(root, path), []byte(content), 0600); err != nil {
+			t.Fatal(err)
+		}
+	}
+	main := configkit.Input{Source: configkit.File(filepath.Join(base, "main.yml")), Filesystem: &configkit.FilesystemContext{Root: root}}
+	result, err := configkit.LoadLayered(main, configkit.LayeredOptions[layeredFacadeConfig]{Overlay: "test"})
+	if err != nil {
+		t.Fatalf("%v: %#v", err, err.(*configkit.LoadError).Diagnostics())
+	}
+	if result.Config.Count != 2 {
+		t.Fatalf("derived overlay = %d", result.Config.Count)
+	}
+	result, err = configkit.LoadLayered(main, configkit.LayeredOptions[layeredFacadeConfig]{Overlay: "test", OverlayFilesystem: &configkit.FilesystemContext{Root: root, BaseDir: base}})
+	if err != nil {
+		t.Fatalf("%v: %#v", err, err.(*configkit.LoadError).Diagnostics())
+	}
+	if result.Config.Count != 3 {
+		t.Fatalf("explicit overlay = %d", result.Config.Count)
+	}
+	result, err = configkit.LoadLayered(configkit.Input{Source: configkit.NoSource()}, configkit.LayeredOptions[layeredFacadeConfig]{Overlay: "test", OverlayFallback: &configkit.FilesystemContext{Root: root, BaseDir: base}})
+	if err != nil {
+		t.Fatalf("%v: %#v", err, err.(*configkit.LoadError).Diagnostics())
+	}
+	if result.Config.Count != 2 {
+		t.Fatalf("fallback overlay = %d", result.Config.Count)
+	}
+}
+
+func TestLayeredOverlayNativeContext(t *testing.T) {
+	filesystem := configkit.NewFilesystem("bundle", fstest.MapFS{
+		"dir/main.yml":          &fstest.MapFile{Data: []byte("count: 1\n")},
+		"dir/overlays/test.yml": &fstest.MapFile{Data: []byte("count: 9\n")},
+	})
+	main := configkit.Input{Source: filesystem.File("dir/main.yml"), Filesystem: &configkit.FilesystemContext{Root: ".", FS: &filesystem}}
+	result, err := configkit.LoadLayered(main, configkit.LayeredOptions[layeredFacadeConfig]{Overlay: "test"})
+	if err != nil {
+		t.Fatalf("%v: %#v", err, err.(*configkit.LoadError).Diagnostics())
+	}
+	if result.Config.Count != 9 {
+		t.Fatalf("config = %#v", result.Config)
+	}
+	_, err = configkit.LoadLayered(main, configkit.LayeredOptions[layeredFacadeConfig]{Overlay: "missing", OverlayFallback: &configkit.FilesystemContext{Root: ".", BaseDir: ".", FS: &filesystem}})
+	if err == nil {
+		t.Fatal("missing selected overlay succeeded")
+	}
+	for _, diagnostic := range err.(*configkit.LoadError).Diagnostics() {
+		if diagnostic.Code == configkit.CodeOverlayMissing {
+			return
+		}
+	}
+	t.Fatalf("diagnostics = %#v", err.(*configkit.LoadError).Diagnostics())
+}