@formspec/build

Build-time schema generation for FormSpec.

This package covers:

• Chain DSL to JSON Schema / UI Schema compilation
• Static analysis of TypeScript classes, interfaces, and type aliases with TSDoc tags
• Mixed-authoring schema generation
• Extension-aware schema generation with custom vendor keywords

Install

pnpm add @formspec/build

Most app code can use formspec, but use @formspec/build directly when you need static analysis or lower-level generation APIs.

Public Entry Points

Chain DSL Generation

import { buildFormSchemas } from "@formspec/build";
import { field, formspec } from "@formspec/dsl";

const form = formspec(
  field.text("name", { required: true }),
  field.enum("status", ["draft", "published"] as const)
);

const { jsonSchema, uiSchema } = buildFormSchemas(form);

Static Analysis

generateSchemas() is the main entry point for TSDoc-backed generation.

import { generateSchemas } from "@formspec/build";

const { jsonSchema, uiSchema } = generateSchemas({
  filePath: "./src/forms.ts",
  typeName: "ProductConfig",
});

generateSchemasFromClass() remains available when the input is definitely a class declaration.

import { generateSchemasFromClass } from "@formspec/build";

const result = generateSchemasFromClass({
  filePath: "./src/forms.ts",
  className: "ProductConfig",
});

Static Build Context

Use the static build context APIs when you need to inspect exports, declarations, or method signatures before deciding what schemas to generate.

Public helpers in this workflow:

• createStaticBuildContext(filePath) - Create a reusable compiler-backed context from a file.
• createStaticBuildContextFromProgram(program, filePath) - Reuse a host-owned ts.Program.
• resolveModuleExport(context, exportName?) - Resolve any exported symbol, including functions and other non-schema declarations.
• resolveModuleExportDeclaration(context, exportName?) - Resolve only schema-source declarations (class, interface, type alias).
• resolveDeclarationMetadata(...) - Resolve metadata for named types, methods, and properties using FormSpec's active metadata policy.
• generateSchemasFromDeclaration(...) - Generate from a resolved schema-source declaration.
• generateSchemasFromParameter(...) - Generate from a method or function parameter declaration.
• generateSchemasFromReturnType(...) - Generate from a method or function return type, unwrapping awaited Promise<T>-style returns before generation.
• generateSchemasFromType(...) - Generate directly from a resolved ts.Type.

Use resolveModuleExportDeclaration(...) when your tooling wants to hand a resolved declaration straight to generateSchemasFromDeclaration(...). Use resolveModuleExport(...) when you need lower-level TypeScript access first, for example to inspect a function export and then generate schemas from one of its signature types.

import * as ts from "typescript";
import {
  createStaticBuildContext,
  generateSchemasFromDeclaration,
  generateSchemasFromParameter,
  generateSchemasFromReturnType,
  resolveDeclarationMetadata,
  resolveModuleExport,
  resolveModuleExportDeclaration,
} from "@formspec/build";

const context = createStaticBuildContext("./src/service.ts");
const serviceDeclaration = resolveModuleExportDeclaration(context, "PaymentService");

if (serviceDeclaration && ts.isClassDeclaration(serviceDeclaration)) {
  const submitMethod = serviceDeclaration.members.find(
    (member): member is ts.MethodDeclaration =>
      ts.isMethodDeclaration(member) &&
      ts.isIdentifier(member.name) &&
      member.name.text === "submit"
  );

  if (submitMethod?.parameters[0]) {
    const methodMetadata = resolveDeclarationMetadata({
      context,
      declaration: submitMethod,
    });
    const inputSchemas = generateSchemasFromParameter({
      context,
      parameter: submitMethod.parameters[0],
    });
  }
}

const inputDeclaration = resolveModuleExportDeclaration(context, "SubmitInput");
if (inputDeclaration) {
  const inputSchemas = generateSchemasFromDeclaration({
    context,
    declaration: inputDeclaration,
  });
}

const paymentSymbol = resolveModuleExport(context, "submitPayment");
const paymentDeclaration = paymentSymbol?.declarations?.find(ts.isFunctionDeclaration);
if (paymentDeclaration) {
  const outputSchemas = generateSchemasFromReturnType({
    context,
    declaration: paymentDeclaration,
  });
}

If you already own a ts.Program, use createStaticBuildContextFromProgram(program, filePath) instead of letting FormSpec create one. If your tool has already resolved a raw ts.Type or signature declaration, use generateSchemasFromType(...) or generateSchemasFromReturnType(...) directly.

This is the supported public path for build-time analysis workflows that used to require @formspec/build/internals.

Supported TSDoc Examples

export interface ProductConfig {
  /** @displayName Product Name @minLength 1 */
  name: string;

  /** @format email */
  supportEmail?: string;

  /** @placeholder Search products */
  query?: string;

  /** @minimum 0 @maximum 9999.99 */
  price: number;

  /** @uniqueItems */
  tags: string[];
}

Extension-Aware Generation

Static-analysis and mixed-authoring generation APIs accept extensionRegistry and vendorPrefix. Chain DSL generation accepts vendorPrefix, but not extensionRegistry.

import { createExtensionRegistry, generateSchemas } from "@formspec/build";

const registry = createExtensionRegistry([myExtension]);

const result = generateSchemas({
  filePath: "./src/forms.ts",
  typeName: "Invoice",
  extensionRegistry: registry,
  vendorPrefix: "x-acme",
});

Generation validates canonical IR before emitting schemas. Invalid inputs now fail generation with structured diagnostic codes surfaced in the thrown error.

Handling Generation Failures

Static generation now uses explicit error reporting on the main entry points:

• generateSchemas({ ..., errorReporting: "throw" }) and generateSchemasFromProgram({ ..., errorReporting: "throw" }) keep the simple throw-on-error contract.
• generateSchemas({ ..., errorReporting: "diagnostics" }) and generateSchemasFromProgram({ ..., errorReporting: "diagnostics" }) return structured diagnostics instead of throwing for analysis and validation failures.
• generateSchemasBatch() and generateSchemasBatchFromProgram() continue to return per-target diagnostics across multiple targets.

Use the "throw" mode when you want "schema or failure" ergonomics. Use the "diagnostics" mode when you want to surface as much feedback as possible in one pass, especially in editor, CI, or migration tooling. The older generateSchemasDetailed() and generateSchemasFromProgramDetailed() wrappers remain available only as deprecated compatibility shims.

import { generateSchemas, generateSchemasBatch } from "@formspec/build";

try {
  const { jsonSchema, uiSchema } = generateSchemas({
    filePath: "./src/forms.ts",
    typeName: "Invoice",
    errorReporting: "throw",
  });
} catch (error) {
  const message = error instanceof Error ? error.message : String(error);

  if (message.includes("UNSUPPORTED_CUSTOM_TYPE_OVERRIDE")) {
    // An extension tried to override a TS global built-in such as Date or Array
  } else if (message.includes("SYNTHETIC_SETUP_FAILURE")) {
    // Extension setup failed before tag type-checking could run
  } else if (message.includes("TYPE_MISMATCH")) {
    // A tag was applied to an incompatible field or target type
  }

  throw error;
}

const detailed = generateSchemas({
  filePath: "./src/forms.ts",
  typeName: "Invoice",
  errorReporting: "diagnostics",
});

if (!detailed.ok) {
  for (const diagnostic of detailed.diagnostics) {
    console.error(`${diagnostic.code}: ${diagnostic.message}`);
  }
}

const batch = generateSchemasBatch({
  targets: [
    { filePath: "./src/forms.ts", typeName: "Invoice" },
    { filePath: "./src/forms.ts", typeName: "PaymentTerms" },
  ],
});

for (const result of batch) {
  if (!result.ok) {
    console.error(
      `${result.typeName} failed: ${result.diagnostics.map((diagnostic) => diagnostic.code).join(", ")}`
    );
  }
}

The most relevant codes for extension-backed static analysis failures are:

• UNSUPPORTED_CUSTOM_TYPE_OVERRIDE for extension custom types that conflict with unsupported TypeScript global built-ins.
• SYNTHETIC_SETUP_FAILURE for invalid or conflicting extension custom type registrations and other synthetic compiler setup failures.
• TYPE_MISMATCH for normal tag-on-type incompatibilities in author source.
• TYPE_NOT_FOUND when a requested exported target cannot be resolved.
• UNSUPPORTED_ROOT_TYPE and DUPLICATE_ROOT_PROPERTIES when a requested type alias cannot be treated as a schema root.
• PROGRAM_CONTEXT_FAILURE when the package cannot create or reuse a TypeScript program for the requested file.

As a rule of thumb, UNSUPPORTED_CUSTOM_TYPE_OVERRIDE and SYNTHETIC_SETUP_FAILURE indicate extension configuration problems, while TYPE_MISMATCH usually indicates an authoring error in the analyzed source.

Internal Entry Point

Low-level canonical IR generators, analyzer primitives, and validation helpers are intentionally no longer exported from the package root. If you need those unstable internals inside the monorepo, import them from @formspec/build/internals.

Main Exports

• buildFormSchemas(form, options?)
• generateJsonSchema(form, options?)
• generateUiSchema(form)
• writeSchemas(form, options)
• generateSchemas(options)
• generateSchemasFromClass(options)
• generateSchemasFromProgram(options)
• generateSchemasBatch(options)
• generateSchemasBatchFromProgram(options)
• buildMixedAuthoringSchemas(options)
• createExtensionRegistry(extensions)

writeSchemas() is the chain-DSL convenience wrapper for writing emitted files. Extension registries apply to the static-analysis and mixed-authoring generation flows above, not to writeSchemas().

License

This package is part of the FormSpec monorepo and is released under the MIT License. See LICENSE for details.