Add min, max and length constraints to CheckboxesField

package.json

@@ -83,7 +83,7 @@
   },
   "license": "SEE LICENSE IN LICENSE",
   "dependencies": {
-    "@defra/forms-model": "^3.0.644",
+    "@defra/forms-model": "^3.0.647",
     "@defra/hapi-tracing": "^1.29.0",
     "@defra/interactive-map": "^0.0.17-alpha",
     "@elastic/ecs-pino-format": "^1.5.0",

src/server/plugins/engine/components/CheckboxesField.test.ts

@@ -173,6 +173,61 @@ describe.each([
         )
       })
 
+      it('is configured with min/max items', () => {
+        const collectionLimited = new ComponentCollection(
+          [{ ...def, schema: { min: 2, max: 4 } }],
+          { model }
+        )
+        const { formSchema } = collectionLimited
+        const { keys } = formSchema.describe()
+
+        expect(keys).toHaveProperty(
+          'myComponent',
+          expect.objectContaining({
+            items: [
+              {
+                allow: options.allow,
+                flags: {
+                  label: def.shortDescription,
+                  only: true
+                },
+                type: options.list.type
+              }
+            ],
+            rules: [
+              { args: { limit: 2 }, name: 'min' },
+              { args: { limit: 4 }, name: 'max' }
+            ]
+          })
+        )
+      })
+
+      it('is configured with length items', () => {
+        const collectionLimited = new ComponentCollection(
+          [{ ...def, schema: { length: 3 } }],
+          { model }
+        )
+        const { formSchema } = collectionLimited
+        const { keys } = formSchema.describe()
+
+        expect(keys).toHaveProperty(
+          'myComponent',
+          expect.objectContaining({
+            items: [
+              {
+                allow: options.allow,
+                flags: {
+                  label: def.shortDescription,
+                  only: true
+                },
+                type: options.list.type
+              }
+            ],
+            rules: [{ args: { limit: 3 }, name: 'length' }]
+          })
+        )
+      })
+
       it('adds errors for empty value', () => {
         const result = collection.validate(getFormData())
 
@@ -386,7 +441,7 @@ describe.each([
       it('should return errors', () => {
         const errors = field.getAllPossibleErrors()
         expect(errors.baseErrors).not.toBeEmpty()
-        expect(errors.advancedSettingsErrors).toBeEmpty()
+        expect(errors.advancedSettingsErrors).not.toBeEmpty()
       })
     })
 

src/server/plugins/engine/components/CheckboxesField.ts

@@ -5,14 +5,17 @@ import { isFormValue } from '~/src/server/plugins/engine/components/FormComponen
 import { SelectionControlField } from '~/src/server/plugins/engine/components/SelectionControlField.js'
 import { type FormModel } from '~/src/server/plugins/engine/models/FormModel.js'
 import { type QuestionPageController } from '~/src/server/plugins/engine/pageControllers/QuestionPageController.js'
+import { messageTemplate } from '~/src/server/plugins/engine/pageControllers/validationOptions.js'
 import {
+  type ErrorMessageTemplateList,
   type FormState,
   type FormStateValue,
   type FormSubmissionState
 } from '~/src/server/plugins/engine/types.js'
 
 export class CheckboxesField extends SelectionControlField {
   declare options: CheckboxesFieldComponent['options']
+  declare schema: CheckboxesFieldComponent['schema']
   declare formSchema: ArraySchema<string> | ArraySchema<number>
   declare stateSchema: ArraySchema<string> | ArraySchema<number>
 
@@ -24,6 +27,7 @@ export class CheckboxesField extends SelectionControlField {
 
     const { listType: type } = this
     const { options } = def
+    const schema = 'schema' in def ? def.schema : {}
 
     let formSchema =
       type === 'string' ? joi.array<string>() : joi.array<number>()
@@ -42,6 +46,18 @@ export class CheckboxesField extends SelectionControlField {
       formSchema = formSchema.optional()
     }
 
+    if (typeof schema?.length === 'number') {
+      formSchema = formSchema.length(schema.length)
+    } else {
+      if (typeof schema?.min === 'number') {
+        formSchema = formSchema.min(schema.min)
+      }
+
+      if (typeof schema?.max === 'number') {
+        formSchema = formSchema.max(schema.max)
+      }
+    }
+
     this.formSchema = formSchema.default([])
     this.stateSchema = formSchema.default(null).allow(null)
     this.options = options
@@ -112,6 +128,30 @@ export class CheckboxesField extends SelectionControlField {
     return this.getContextValueFromFormValue(values)
   }
 
+  /**
+   * For error preview page that shows all possible errors on a component
+   */
+  getAllPossibleErrors(): ErrorMessageTemplateList {
+    return CheckboxesField.getAllPossibleErrors()
+  }
+
+  /**
+   * Static version of getAllPossibleErrors that doesn't require a component instance.
+   */
+  static getAllPossibleErrors(): ErrorMessageTemplateList {
+    const parentErrors = SelectionControlField.getAllPossibleErrors()
+
+    return {
+      ...parentErrors,
+      advancedSettingsErrors: [
+        ...parentErrors.advancedSettingsErrors,
+        { type: 'array.min', template: messageTemplate.arrayMin },
+        { type: 'array.max', template: messageTemplate.arrayMax },
+        { type: 'array.length', template: messageTemplate.arrayLength }
+      ]
+    }
+  }
+
   isValue(value?: FormStateValue | FormState): value is Item['value'][] {
     if (!Array.isArray(value)) {
       return false

src/server/plugins/engine/pageControllers/validationOptions.ts

@@ -61,7 +61,10 @@ export const messageTemplate: Record<string, JoiExpression> = {
   ) as JoiExpression,
   dateFormat: '{{#title}} must be a real date',
   dateMin: '{{#title}} must be the same as or after {{#limit}}',
-  dateMax: '{{#title}} must be the same as or before {{#limit}}'
+  dateMax: '{{#title}} must be the same as or before {{#limit}}',
+  arrayMax: 'Only {{#limit}} can be selected from the list',
+  arrayMin: 'Select at least {{#limit}} options from the list',
+  arrayLength: 'Select only {{#limit}} options from the list'
 }
 
 export const messages: LanguageMessagesExt = {