feat(validator): enhance mapping validation to include list refs

Updated validation logic to ensure at least one mapping is provided,
including support for file and directory list references.
Added comprehensive tests to cover various mapping scenarios.

Author: mrz1836

internal/config/validator.go

@@ -506,8 +506,8 @@ func (t *TargetConfig) validateWithLogging(ctx context.Context, logConfig *loggi
 	default:
 	}
 
-	// Validate that we have at least one file or directory mapping
-	if len(t.Files) == 0 && len(t.Directories) == 0 {
+	// Validate that we have at least one file or directory mapping (direct or via list refs)
+	if len(t.Files) == 0 && len(t.Directories) == 0 && len(t.FileListRefs) == 0 && len(t.DirectoryListRefs) == 0 {
 		return ErrNoMappings
 	}
 

internal/config/validator_test.go

@@ -550,6 +550,149 @@ func TestTargetConfig_BranchValidation(t *testing.T) {
 	}
 }
 
+// TestTargetConfig_MappingRequirement tests that targets accept any combination of
+// direct mappings or list refs, and reject targets with none.
+func TestTargetConfig_MappingRequirement(t *testing.T) {
+	tests := []struct {
+		name      string
+		target    TargetConfig
+		expectErr bool
+	}{
+		{
+			name: "valid - files only",
+			target: TargetConfig{
+				Repo:  "org/target",
+				Files: []FileMapping{{Src: "a.txt", Dest: "a.txt"}},
+			},
+		},
+		{
+			name: "valid - directories only",
+			target: TargetConfig{
+				Repo:        "org/target",
+				Directories: []DirectoryMapping{{Src: "src", Dest: "dest"}},
+			},
+		},
+		{
+			name: "valid - file list refs only",
+			target: TargetConfig{
+				Repo:         "org/target",
+				FileListRefs: []string{"common-files"},
+			},
+		},
+		{
+			name: "valid - directory list refs only",
+			target: TargetConfig{
+				Repo:              "org/target",
+				DirectoryListRefs: []string{"github-workflows"},
+			},
+		},
+		{
+			name: "valid - file list refs and directory list refs",
+			target: TargetConfig{
+				Repo:              "org/target",
+				FileListRefs:      []string{"common-files", "editor-config"},
+				DirectoryListRefs: []string{"github-workflows", "vs-code"},
+			},
+		},
+		{
+			name: "valid - files and directories",
+			target: TargetConfig{
+				Repo:        "org/target",
+				Files:       []FileMapping{{Src: "a.txt", Dest: "a.txt"}},
+				Directories: []DirectoryMapping{{Src: "src", Dest: "dest"}},
+			},
+		},
+		{
+			name: "valid - all four mapping types",
+			target: TargetConfig{
+				Repo:              "org/target",
+				Files:             []FileMapping{{Src: "a.txt", Dest: "a.txt"}},
+				Directories:       []DirectoryMapping{{Src: "src", Dest: "dest"}},
+				FileListRefs:      []string{"common-files"},
+				DirectoryListRefs: []string{"github-workflows"},
+			},
+		},
+		{
+			name: "invalid - no mappings at all",
+			target: TargetConfig{
+				Repo: "org/target",
+			},
+			expectErr: true,
+		},
+		{
+			name: "invalid - empty slices for all mapping types",
+			target: TargetConfig{
+				Repo:              "org/target",
+				Files:             []FileMapping{},
+				Directories:       []DirectoryMapping{},
+				FileListRefs:      []string{},
+				DirectoryListRefs: []string{},
+			},
+			expectErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctx := context.Background()
+			logger := logrus.NewEntry(logrus.StandardLogger())
+
+			err := tt.target.validateWithLogging(ctx, nil, logger)
+
+			if tt.expectErr {
+				require.Error(t, err)
+				assert.ErrorIs(t, err, ErrNoMappings)
+			} else {
+				assert.NoError(t, err)
+			}
+		})
+	}
+}
+
+// TestTargetConfig_ListRefsOnlyFullValidation verifies that a target with only list refs
+// passes full config-level validation (the real-world scenario that was broken).
+func TestTargetConfig_ListRefsOnlyFullValidation(t *testing.T) {
+	config := &Config{
+		Version: 1,
+		FileLists: []FileList{
+			{
+				ID:   "common-files",
+				Name: "Common Files",
+				Files: []FileMapping{
+					{Src: ".editorconfig", Dest: ".editorconfig"},
+				},
+			},
+		},
+		DirectoryLists: []DirectoryList{
+			{
+				ID:   "github-workflows",
+				Name: "GitHub Workflows",
+				Directories: []DirectoryMapping{
+					{Src: ".github/workflows", Dest: ".github/workflows"},
+				},
+			},
+		},
+		Groups: []Group{
+			{
+				Name:   "test-group",
+				ID:     "test-group",
+				Source: SourceConfig{Repo: "org/source", Branch: "main"},
+				Targets: []TargetConfig{
+					{
+						Repo:              "org/target",
+						FileListRefs:      []string{"common-files"},
+						DirectoryListRefs: []string{"github-workflows"},
+						Transform:         Transform{RepoName: true},
+					},
+				},
+			},
+		},
+	}
+
+	err := config.Validate()
+	assert.NoError(t, err)
+}
+
 // TestValidate_DuplicateFileDestinations verifies that duplicate file destinations
 // within the same target are detected
 func TestValidate_DuplicateFileDestinations(t *testing.T) {