mcp: fix multi-select enum elicitation

mcp/client.go

@@ -710,8 +710,10 @@ func validateElicitProperty(propName string, propSchema *jsonschema.Schema) erro
 		return validateElicitNumberProperty(propName, propSchema)
 	case "boolean":
 		return validateElicitBooleanProperty(propName, propSchema)
+	case "array":
+		return validateElicitArrayProperty(propName, propSchema)
 	default:
-		return fmt.Errorf("elicit schema property %q has unsupported type %q, only string, number, integer, and boolean are allowed", propName, propSchema.Type)
+		return fmt.Errorf("elicit schema property %q has unsupported type %q, only string, number, integer, boolean, and array are allowed", propName, propSchema.Type)
 	}
 }
 
@@ -724,7 +726,7 @@ func validateElicitStringProperty(propName string, propSchema *jsonschema.Schema
 			return fmt.Errorf("elicit schema property %q has enum values but type is %q, enums are only supported for string type", propName, propSchema.Type)
 		}
 		// Enum values themselves are validated by the JSON schema library
-		// Validate enumNames if present - must match enum length
+		// Validate legacy enumNames if present - must match enum length.
 		if propSchema.Extra != nil {
 			if enumNamesRaw, exists := propSchema.Extra["enumNames"]; exists {
 				// Type check enumNames - should be a slice
@@ -739,6 +741,15 @@ func validateElicitStringProperty(propName string, propSchema *jsonschema.Schema
 		}
 		return nil
 	}
+	// Handle new style of titled enums.
+	if propSchema.OneOf != nil {
+		for _, entry := range propSchema.OneOf {
+			if err := validateTitledEnumEntry(entry); err != nil {
+				return fmt.Errorf("elicit schema property %q oneOf has invalid entry: %v", propName, err)
+			}
+		}
+		return nil
+	}
 
 	// Validate format if specified - only specific formats are allowed
 	if propSchema.Format != "" {
@@ -791,6 +802,53 @@ func validateElicitNumberProperty(propName string, propSchema *jsonschema.Schema
 	return nil
 }
 
+// validateElicitArrayProperty validates multi-select enum properties.
+func validateElicitArrayProperty(propName string, propSchema *jsonschema.Schema) error {
+	if propSchema.Items == nil {
+		return fmt.Errorf("elicit schema property %q is array but missing 'items' definition", propName)
+	}
+
+	items := propSchema.Items
+	switch items.Type {
+	case "string":
+		// Untitled enums.
+		if items.Enum == nil {
+			return fmt.Errorf("elicit schema property %q items must specify enum for untitled enums", propName)
+		}
+		return nil
+	case "":
+		// Titled enums.
+		if len(items.AnyOf) == 0 {
+			return fmt.Errorf("elicit schema property %q items must specify anyOf for titled enums", propName)
+		}
+		for _, entry := range items.AnyOf {
+			if err := validateTitledEnumEntry(entry); err != nil {
+				return fmt.Errorf("elicit schema property %q items has invalid entry: %v", propName, err)
+			}
+		}
+		return nil
+	default:
+		return fmt.Errorf("elicit schema property %q items have unsupported type %q", propName, items.Type)
+	}
+}
+
+func validateTitledEnumEntry(entry *jsonschema.Schema) error {
+	if entry.Const == nil {
+		return fmt.Errorf("const is required for titled enum entries")
+	}
+	constVal, ok := (*entry.Const).(string)
+	if !ok {
+		return fmt.Errorf("const must be a string for titled enum entries")
+	}
+	if constVal == "" {
+		return fmt.Errorf("const cannot be empty for titled enum entries")
+	}
+	if entry.Title == "" {
+		return fmt.Errorf("title is required for titled enum entries")
+	}
+	return nil
+}
+
 // validateElicitBooleanProperty validates boolean-type properties.
 func validateElicitBooleanProperty(propName string, propSchema *jsonschema.Schema) error {
 	return validateDefaultProperty[bool](propName, propSchema)

mcp/mcp_test.go

@@ -1095,7 +1095,7 @@ func TestElicitationSchemaValidation(t *testing.T) {
 			},
 		},
 		{
-			name: "string enum",
+			name: "single select untitled enum",
 			schema: &jsonschema.Schema{
 				Type: "object",
 				Properties: map[string]*jsonschema.Schema{
@@ -1111,7 +1111,7 @@ func TestElicitationSchemaValidation(t *testing.T) {
 			},
 		},
 		{
-			name: "enum with matching enumNames",
+			name: "legacy titled enum",
 			schema: &jsonschema.Schema{
 				Type: "object",
 				Properties: map[string]*jsonschema.Schema{
@@ -1130,7 +1130,7 @@ func TestElicitationSchemaValidation(t *testing.T) {
 			},
 		},
 		{
-			name: "enum with enum schema",
+			name: "single select titled enum",
 			schema: &jsonschema.Schema{
 				Type: "object",
 				Properties: map[string]*jsonschema.Schema{
@@ -1138,22 +1138,62 @@ func TestElicitationSchemaValidation(t *testing.T) {
 						Type: "string",
 						OneOf: []*jsonschema.Schema{
 							{
-								Const: anyPtr(map[string]string{
+								Const: anyPtr("high"),
-									"const": "high",
+								Title: "High Priority",
-									"title": "High Priority",
-								}),
 							},
 							{
-								Const: anyPtr(map[string]string{
+								Const: anyPtr("medium"),
-									"const": "medium",
+								Title: "Medium Priority",
-									"title": "Medium Priority",
-								}),
 							},
 							{
-								Const: anyPtr(map[string]string{
+								Const: anyPtr("low"),
-									"const": "low",
+								Title: "Low Priority",
-									"title": "Low Priority",
+							},
-								}),
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "multi select untitled enum",
+			schema: &jsonschema.Schema{
+				Type: "object",
+				Properties: map[string]*jsonschema.Schema{
+					"status": {
+						Type: "array",
+						Items: &jsonschema.Schema{
+							Type: "string",
+							Enum: []any{
+								"active",
+								"inactive",
+								"pending",
+							},
+						},
+					},
+				},
+			},
+		},
+		{
+			name: "multi select titled enum",
+			schema: &jsonschema.Schema{
+				Type: "object",
+				Properties: map[string]*jsonschema.Schema{
+					"priority": {
+						Type: "array",
+						Items: &jsonschema.Schema{
+							AnyOf: []*jsonschema.Schema{
+								{
+									Const: anyPtr("high"),
+									Title: "High Priority",
+								},
+								{
+									Const: anyPtr("medium"),
+									Title: "Medium Priority",
+								},
+								{
+									Const: anyPtr("low"),
+									Title: "Low Priority",
+								},
 							},
 						},
 					},
@@ -1210,17 +1250,7 @@ func TestElicitationSchemaValidation(t *testing.T) {
 					"config": {Type: "object"},
 				},
 			},
-			expectedError: "elicit schema property \"config\" has unsupported type \"object\", only string, number, integer, and boolean are allowed",
+			expectedError: "elicit schema property \"config\" has unsupported type \"object\", only string, number, integer, boolean, and array are allowed",
-		},
-		{
-			name: "array property",
-			schema: &jsonschema.Schema{
-				Type: "object",
-				Properties: map[string]*jsonschema.Schema{
-					"tags": {Type: "array", Items: &jsonschema.Schema{Type: "string"}},
-				},
-			},
-			expectedError: "elicit schema property \"tags\" has unsupported type \"array\", only string, number, integer, and boolean are allowed",
 		},
 		{
 			name: "array without items",
@@ -1230,7 +1260,27 @@ func TestElicitationSchemaValidation(t *testing.T) {
 					"items": {Type: "array"},
 				},
 			},
-			expectedError: "elicit schema property \"items\" has unsupported type \"array\", only string, number, integer, and boolean are allowed",
+			expectedError: "elicit schema property \"items\" is array but missing 'items' definition",
+		},
+		{
+			name: "array with integer items",
+			schema: &jsonschema.Schema{
+				Type: "object",
+				Properties: map[string]*jsonschema.Schema{
+					"items": {Type: "array", Items: &jsonschema.Schema{Type: "integer"}},
+				},
+			},
+			expectedError: "elicit schema property \"items\" items have unsupported type \"integer\"",
+		},
+		{
+			name: "array of generic strings",
+			schema: &jsonschema.Schema{
+				Type: "object",
+				Properties: map[string]*jsonschema.Schema{
+					"items": {Type: "array", Items: &jsonschema.Schema{Type: "string"}},
+				},
+			},
+			expectedError: "elicit schema property \"items\" items must specify enum for untitled enums",
 		},
 		{
 			name: "unsupported string format",
@@ -1385,7 +1435,29 @@ func TestElicitationSchemaValidation(t *testing.T) {
 					},
 				},
 			},
-			expectedError: "elicit schema property \"priority\" has unsupported type \"\", only string, number, integer, and boolean are allowed",
+			expectedError: "elicit schema property \"priority\" has unsupported type \"\", only string, number, integer, boolean, and array are allowed",
+		},
+		{
+			name: "titled enum without const",
+			schema: &jsonschema.Schema{
+				Type: "object",
+				Properties: map[string]*jsonschema.Schema{
+					"priority": {
+						Type: "string",
+						OneOf: []*jsonschema.Schema{
+							{
+								Const: anyPtr("high"),
+								Title: "High Priority",
+							},
+							{
+								Type:  "string",
+								Title: "Other Priority",
+							},
+						},
+					},
+				},
+			},
+			expectedError: "elicit schema property \"priority\" oneOf has invalid entry: const is required for titled enum entries",
 		},
 		{
 			name: "untyped property",
@@ -1395,7 +1467,7 @@ func TestElicitationSchemaValidation(t *testing.T) {
 					"data": {},
 				},
 			},
-			expectedError: "elicit schema property \"data\" has unsupported type \"\", only string, number, integer, and boolean are allowed",
+			expectedError: "elicit schema property \"data\" has unsupported type \"\", only string, number, integer, boolean, and array are allowed",
 		},
 	}
 
@@ -1458,10 +1530,8 @@ func TestElicitContentValidation(t *testing.T) {
 						Type: "string",
 						OneOf: []*jsonschema.Schema{
 							{
-								Const: anyPtr(map[string]string{
+								Const: anyPtr("high"),
-									"const": "high",
+								Title: "High Priority",
-									"title": "High Priority",
-								}),
 							},
 						},
 					},
@@ -1478,10 +1548,8 @@ func TestElicitContentValidation(t *testing.T) {
 						Type: "string",
 						OneOf: []*jsonschema.Schema{
 							{
-								Const: anyPtr(map[string]string{
+								Const: anyPtr("potato"),
-									"const": "potato",
+								Title: "Potato Priority",
-									"title": "Potato Priority",
-								}),
 							},
 						},
 					},