Source Cursor rule: .cursor/rules/forms.mdc. Original Cursor alwaysApply: false.

Forms: React Hook Form + Zod

All forms MUST use React Hook Form with Zod validation.

Basic Pattern

import { zodResolver } from '@hookform/resolvers/zod';
import { useForm } from 'react-hook-form';
import { z } from 'zod';
import { Button, Input } from '@trycompai/design-system';

// 1. Define schema
const formSchema = z.object({
  email: z.string().email('Invalid email'),
  password: z.string().min(8, 'Min 8 characters'),
});

// 2. Infer type
type FormData = z.infer<typeof formSchema>;

// 3. Use in component
function MyForm() {
  const {
    register,
    handleSubmit,
    formState: { errors, isSubmitting },
  } = useForm<FormData>({
    resolver: zodResolver(formSchema),
  });

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <Input {...register('email')} />
      {errors.email && <p>{errors.email.message}</p>}
      
      <Button type="submit" loading={isSubmitting}>
        Submit
      </Button>
    </form>
  );
}

Zod Schema Patterns

const profileSchema = z.object({
  // Strings
  name: z.string().min(1, 'Required'),
  email: z.string().email(),
  website: z.string().url().optional(),
  
  // Numbers (coerce for inputs)
  age: z.coerce.number().int().min(0),
  price: z.coerce.number().positive(),
  
  // Arrays
  tags: z.array(z.string()).min(1),
  
  // Enums
  status: z.enum(['active', 'inactive']),
});

// Cross-field validation
const passwordSchema = z.object({
  password: z.string().min(8),
  confirmPassword: z.string(),
}).refine(d => d.password === d.confirmPassword, {
  message: "Passwords don't match",
  path: ['confirmPassword'],
});

Controller for Complex Components

import { Controller } from 'react-hook-form';
import { Select, SelectContent, SelectItem, SelectTrigger } from '@trycompai/design-system';

<Controller
  name="status"
  control={control}
  render={({ field }) => (
    <Select onValueChange={field.onChange} value={field.value}>
      <SelectTrigger>{field.value || 'Select...'}</SelectTrigger>
      <SelectContent>
        <SelectItem value="active">Active</SelectItem>
        <SelectItem value="inactive">Inactive</SelectItem>
      </SelectContent>
    </Select>
  )}
/>

Form State

const {
  register,
  handleSubmit,
  control,
  watch,           // Watch field values
  setValue,        // Set field programmatically
  reset,           // Reset form
  setError,        // Set error manually
  formState: {
    errors,        // Field errors
    isSubmitting,  // Submitting
    isValid,       // All valid
    isDirty,       // Modified
  },
} = useForm<FormData>({
  resolver: zodResolver(schema),
  mode: 'onChange', // Validate on change
});

Error Handling

const onSubmit = async (data: FormData) => {
  try {
    await submitToApi(data);
  } catch (error) {
    // Field-specific error
    setError('email', { message: 'Email taken' });
    // Or root error
    setError('root', { message: 'Something went wrong' });
  }
};

// Display root error
{errors.root && <p>{errors.root.message}</p>}

Dynamic Fields

import { useFieldArray } from 'react-hook-form';

const { fields, append, remove } = useFieldArray({
  control,
  name: 'items',
});

{fields.map((field, index) => (
  <div key={field.id}>
    <Input {...register(`items.${index}.name`)} />
    <Button type="button" onClick={() => remove(index)}>Remove</Button>
  </div>
))}
<Button type="button" onClick={() => append({ name: '' })}>Add</Button>

Anti-Patterns

// ❌ useState for form fields
const [email, setEmail] = useState('');

// ❌ Manual validation
if (email.length < 5) setError('Too short');

// ❌ Missing button type (defaults to submit)
<Button onClick={handleCancel}>Cancel</Button>

// ✅ Correct
const { register } = useForm();
const schema = z.object({ email: z.string().min(5) });
<Button type="button" onClick={handleCancel}>Cancel</Button>