feat(Form): support rule formatter

src/form/README.md

@@ -442,6 +442,7 @@ export default {
 | validator `v2.5.3` | Custom validator | *(value, rule) => boolean \| Promise* |
 | pattern `v2.5.3` | Regex pattern | *RegExp* |
 | trigger `v2.5.2` | When to validate the form，can be set to `onChange`、`onBlur` | *string* |
+| formatter `v2.5.3` | Format value before validate | *(value) => any* |
 
 ### Events
 

src/form/README.zh-CN.md

@@ -481,6 +481,7 @@ export default {
 | validator `v2.5.3` | 通过函数进行校验 | *(value, rule) => boolean \| Promise* |
 | pattern `v2.5.3` | 通过正则表达式进行校验 | *RegExp* |
 | trigger `v2.5.2` | 本项规则的触发时机，可选值为`onChange`、`onBlur` | *string* |
+| formatter `v2.5.3` | 格式化函数，将表单项的值转换后进行校验 | *(value) => any* |
 
 ### Events
 

src/form/test/props.spec.js

@@ -59,6 +59,35 @@ test('rules prop - pattern', async () => {
   });
 });
 
+test('rules prop - formatter', async () => {
+  const onFailed = jest.fn();
+  const wrapper = mountForm({
+    template: `
+      <van-form @failed="onFailed">
+        <van-field name="A" :rules="rules" value=" " />
+        <van-button native-type="submit" />
+      </van-form>
+    `,
+    data() {
+      return {
+        rules: [
+          { required: true, formatter: val => val.trim(), message: 'foo' },
+        ],
+      };
+    },
+    methods: {
+      onFailed,
+    },
+  });
+
+  await submitForm(wrapper);
+
+  expect(onFailed).toHaveBeenCalledWith({
+    errors: [{ message: 'foo', name: 'A' }],
+    values: { A: ' ' },
+  });
+});
+
 test('rules prop - async validator', async () => {
   const onFailed = jest.fn();
   const wrapper = mountForm({