FOSMVVM Fields Generator

Read [shared/functional-discipline.md](../shared/functional-discipline.md) before proceeding. Every rule below derives from it.

Generate Form Specifications following FOSMVVM patterns.

Conceptual Foundation

For full architecture context, see [FOSMVVMArchitecture.md](../../docs/FOSMVVMArchitecture.md) | [OpenClaw reference]({baseDir}/references/FOSMVVMArchitecture.md)

API catalog: check [../shared/api-catalog/FOSMVVM.md](../shared/api-catalog/FOSMVVM.md) § Forms, § Validation before hand-writing helpers.

A Form Specification (implemented as a {Name}Fields protocol) is the single source of truth for user input. It answers:

1. What data can the user provide? (properties)
2. How should it be presented? (FormField with type, keyboard, autofill semantics)
3. What constraints apply? (validation rules)
4. What messages should be shown? (localized titles, placeholders, errors)

Why This Matters

The Form Specification is defined once, used everywhere:

// Same protocol adopted by different consumers:
struct CreateIdeaRequestBody: ServerRequestBody, IdeaFields { ... }  // HTTP transmission
@ViewModel struct IdeaFormViewModel: IdeaFields { ... }              // Form rendering
final class Idea: Model, IdeaFields { ... }                          // Persistence validation

This ensures:

• Consistent validation - Same rules on client and server
• Shared localization - One YAML file, used everywhere
• Single source of truth - Change once, applies everywhere

← Functional discipline: one input, three projections; duplicating the definition forks the input layer.

Connection to FOSMVVM

Form Specifications integrate with:

• Localization System - FormField titles/placeholders and validation messages use LocalizableString
• Validation System - Implements ValidatableModel protocol
• Request System - RequestBody types adopt Fields for validated transmission
• ViewModel System - ViewModels adopt Fields for form rendering

When to Use This Skill

• Defining a new form (create, edit, filter, search)
• Adding validation to a request body
• Any type that needs to conform to ValidatableModel
• When fosmvvm-fluent-datamodel-generator needs form fields for a DataModel

What This Skill Generates

A complete Form Specification consists of 3 files:

Project Structure Configuration

Replace placeholders with your project's actual paths:

Expected Structure:

Sources/
  {ViewModelsTarget}/
    FieldModels/
      {Name}Fields.swift
      {Name}FieldsMessages.swift
  {ResourcesPath}/
    FieldModels/
      {Name}FieldsMessages.yml

How to Use This Skill

Invocation: /fosmvvm-fields-generator

Prerequisites:

• Form purpose understood from conversation context
• Field requirements discussed (names, types, constraints)
• Entity relationship identified (what is this form creating/editing)

Workflow integration: This skill is used when defining form validation and user input contracts. The skill references conversation context automatically—no file paths or Q&A needed. Often precedes fosmvvm-fluent-datamodel-generator for form-backed models.

Pattern Implementation

This skill references conversation context to determine Fields protocol structure:

Form Analysis

From conversation context, the skill identifies:

• Form purpose (create, edit, filter, login, settings)
• Entity relation (User, Idea, Document - what's being created/edited)
• Protocol naming (CreateIdeaFields, UpdateProfile, LoginCredentials)

Field Design

For each field from requirements:

• Property specification (name, type, optional vs required)
• Presentation type (FormFieldType: text, textArea, select, checkbox)
• Input semantics (FormInputType: email, password, tel, date)
• Constraints (required, length range, value range, date range)
• Localization (title, placeholder, validation error messages)

File Generation Order

1. Fields protocol with FormField definitions and validation
2. FieldsMessages struct with @LocalizedString properties
3. FieldsMessages YAML with localized strings

Context Sources

Skill references information from:

• Prior conversation: Form requirements, field specifications discussed
• Specification files: If Claude has read form specs into context
• Existing patterns: From codebase analysis of similar Fields protocols

Key Patterns

Protocol Structure

public protocol {Name}Fields: ValidatableModel, Codable, Sendable {
    var fieldName: FieldType { get set }
    var {name}ValidationMessages: {Name}FieldsMessages { get }
}

**Overridable-with-a-default member? Declare it as a requirement AND provide the default. If you want a Fields member to have a zero-config default that a conformer can still override (a validation policy, a message source), it must be a protocol requirement** with a default in an extension. A member defined only in an extension is statically dispatched — a conformer's "override" merely shadows it and calls through the protocol/a generic some {Name}Fields still hit the default. That's a silent OCP failure. See [Architecture Patterns → Requirement + Default = a Real Override](../shared/architecture-patterns.md).

The {name}FieldsValidateModel(validations:fields:) composition helper lives in the extension deliberately — it is not an override point (ratified 2026-08-25). Its protocol-derived prefix is the point: a type adopting two Fields protocols writes one validate(fields:validations:) that calls documentFieldsValidateModel(…) and otherFieldsValidateModel(…) — a composition seam, so the requirement-plus-default rule above does not apply to it. (ValidatableModel.validate(fields:validations:) itself is a real requirement, so a validate default in a Fields extension is dynamically dispatched and correctly overridable.)

FormField Definition

static var contentField: FormField<String?> { .init(
    fieldId: .init(id: "content"),
    title: .localized(for: {Name}FieldsMessages.self, propertyName: "content", messageKey: "title"),
    placeholder: .localized(for: {Name}FieldsMessages.self, propertyName: "content", messageKey: "placeholder"),
    type: .textArea(inputType: .text),
    options: [
        .required(value: true)
    ] + FormInputOption.rangeLength(contentRange)
) }

FormField Types Reference

FormInputType Reference (common ones)

Validation Method Pattern

internal func validateContent(_ fields: [FormFieldBase]?) -> [ValidationResult]? {
    guard fields == nil || (fields?.contains(Self.contentField) == true) else {
        return nil
    }

    var result = [ValidationResult]()

    if content.isEmpty {
        result.append(.init(
            status: .error,
            field: Self.contentField,
            message: {name}ValidationMessages.contentRequiredMessage
        ))
    } else if !Self.contentRange.contains(NSString(string: content).length) {
        result.append(.init(
            status: .error,
            field: Self.contentField,
            message: {name}ValidationMessages.contentOutOfRangeMessage
        ))
    }

    return result.isEmpty ? nil : result
}

Messages Struct Pattern

@FieldValidationModel public struct {Name}FieldsMessages {
    @LocalizedString("content", messageGroup: "validationMessages", messageKey: "required")
    public var contentRequiredMessage

    @LocalizedString("content", messageGroup: "validationMessages", messageKey: "outOfRange")
    public var contentOutOfRangeMessage
}

YAML Structure

en:
  {Name}FieldsMessages:
    content:
      title: "Content"
      placeholder: "Enter your content..."
      validationMessages:
        required: "Content is required"
        outOfRange: "Content must be between 1 and 10,000 characters"

Naming Conventions

See Also

• [FOSMVVMArchitecture.md](../../docs/FOSMVVMArchitecture.md) - Full FOSMVVM architecture reference
• [Architecture Patterns → Encapsulation Is the Precondition](../shared/architecture-patterns.md) — encapsulation is the precondition SOLID assumes, not a SOLID checkbox. A Fields contract must express field identity/validation as typed values, never raw String keys/identities (stringly-typing is the encapsulation break — the small hole in the dam). Repo CLAUDE.md → Encapsulation Is the Precondition SOLID Assumes.
• [fosmvvm-viewmodel-generator](../fosmvvm-viewmodel-generator/SKILL.md) - For ViewModels that adopt Fields
• [fosmvvm-fluent-datamodel-generator](../fosmvvm-fluent-datamodel-generator/SKILL.md) - For Fluent DataModels that implement Fields
• [reference.md](reference.md) - Complete file templates

Version History