io-ts-reporters/src/index.ts

Formatting of io-ts validation errors

/**
 * An [io-ts Reporter](https://gcanti.github.io/io-ts/modules/Reporter.ts.html#reporter-interface).
 *
 * @example
 *
 * import * as t from 'io-ts';
 * import Reporter from 'io-ts-reporters';
 *
 * const User = t.interface({ name: t.string });
 *
 * assert.deepEqual(
 *   Reporter.report(User.decode({ nam: 'Jane' })),
 *   ['Expecting string at name but instead got: undefined'],
 * )
 * assert.deepEqual( Reporter.report(User.decode({ name: 'Jane' })), [])
 *
 * @since 1.2.0
 */
import * as A from 'fp-ts/Array'
import * as E from 'fp-ts/Either'
import * as NEA from 'fp-ts/NonEmptyArray'
import * as O from 'fp-ts/Option'
import * as R from 'fp-ts/Record'
import {pipe} from 'fp-ts/pipeable'
import * as t from 'io-ts'
import {Reporter} from 'io-ts/lib/Reporter'

import {takeUntil} from './utils'

const isUnionType = ({type}: t.ContextEntry) => type instanceof t.UnionType

const jsToString = (value: t.mixed) =>
  value === undefined ? 'undefined' : JSON.stringify(value)

const keyPath = (ctx: t.Context) =>
  // The context entry with an empty key is the original
  // type ("default context"), not a type error.
  ctx
    .map((c) => c.key)
    .filter(Boolean)
    .join('.')

// The actual error is last in context
const getErrorFromCtx = (validation: t.ValidationError) =>
  // https://github.com/gcanti/fp-ts/pull/544/files
  A.last(validation.context as t.ContextEntry[])

const getValidationContext = (validation: t.ValidationError) =>
  // https://github.com/gcanti/fp-ts/pull/544/files
  validation.context as t.ContextEntry[]

/**
 * @category internals
 * @since 1.2.1
 */
export const TYPE_MAX_LEN = 160 // Two lines of 80-col text
const truncateType = (type: string, options: ReporterOptions = {}): string => {
  const {truncateLongTypes = true} = options

  if (truncateLongTypes && type.length > TYPE_MAX_LEN) {
    return `${type.slice(0, TYPE_MAX_LEN - 3)}...`
  }

  return type
}

const errorMessageSimple = (
  expectedType: string,
  path: string,
  error: t.ValidationError,
  options?: ReporterOptions,
) =>
  // https://github.com/elm-lang/core/blob/18c9e84e975ed22649888bfad15d1efdb0128ab2/src/Native/Json.js#L199
  [
    `Expecting ${truncateType(expectedType, options)}`,
    path === '' ? '' : `at ${path}`,
    `but instead got: ${jsToString(error.value)}`,
    error.message ? `(${error.message})` : '',
  ]
    .filter(Boolean)
    .join(' ')

const errorMessageUnion = (
  expectedTypes: string[],
  path: string,
  value: unknown,
  options?: ReporterOptions,
) =>
  // https://github.com/elm-lang/core/blob/18c9e84e975ed22649888bfad15d1efdb0128ab2/src/Native/Json.js#L199
  [
    'Expecting one of:\n',
    expectedTypes
      .map((type) => `    ${truncateType(type, options)}`)
      .join('\n'),
    path === '' ? '\n' : `\nat ${path} `,
    `but instead got: ${jsToString(value)}`,
  ]
    .filter(Boolean)
    .join('')

// Find the union type in the list of ContextEntry
// The next ContextEntry should be the type of this branch of the union
const findExpectedType = (ctx: t.ContextEntry[]) =>
  pipe(
    ctx,
    A.findIndex(isUnionType),
    O.chain((n) => A.lookup(n + 1, ctx)),
  )

const formatValidationErrorOfUnion = (
  path: string,
  errors: NEA.NonEmptyArray<t.ValidationError>,
  options?: ReporterOptions,
) => {
  const expectedTypes = pipe(
    errors,
    A.map(getValidationContext),
    A.map(findExpectedType),
    A.compact,
  )

  const value = pipe(
    expectedTypes,
    A.head,
    O.map((v) => v.actual),
    O.getOrElse((): unknown => undefined),
  )

  const expected = expectedTypes.map(({type}) => type.name)

  return expected.length > 0
    ? O.some(errorMessageUnion(expected, path, value, options))
    : O.none
}

const formatValidationCommonError = (
  path: string,
  error: t.ValidationError,
  options?: ReporterOptions,
) =>
  pipe(
    error,
    getErrorFromCtx,
    O.map((errorContext) =>
      errorMessageSimple(errorContext.type.name, path, error, options),
    ),
  )

const groupByKey = NEA.groupBy((error: t.ValidationError) =>
  pipe(error.context, takeUntil(isUnionType), keyPath),
)

const format = (
  path: string,
  errors: NEA.NonEmptyArray<t.ValidationError>,
  options?: ReporterOptions,
) =>
  NEA.tail(errors).length > 0
    ? formatValidationErrorOfUnion(path, errors, options)
    : formatValidationCommonError(path, NEA.head(errors), options)

/**
 * Format a single validation error.
 *
 * @category formatters
 * @since 1.0.0
 */
export const formatValidationError = (
  error: t.ValidationError,
  options?: ReporterOptions,
) => formatValidationCommonError(keyPath(error.context), error, options)

/**
 * Format validation errors (`t.Errors`).
 *
 * @example
 * import * as E from 'fp-ts/Either'
 * import * as t from 'io-ts'
 * import { formatValidationErrors } from 'io-ts-reporters'
 *
 * const result = t.string.decode(123)
 *
 * assert.deepEqual(
 *   E.mapLeft(formatValidationErrors)(result),
 *   E.left(['Expecting string but instead got: 123'])
 * )
 *
 * @category formatters
 * @since 1.2.0
 */
export const formatValidationErrors = (
  errors: t.Errors,
  options?: ReporterOptions,
) =>
  pipe(
    errors,
    groupByKey,
    R.mapWithIndex((path, errors) => format(path, errors, options)),
    R.compact,
    R.toArray,
    A.map(([_key, error]) => error),
  )

/**
 * @category formatters
 * @since 1.2.2
 */
export interface ReporterOptions {
  truncateLongTypes?: boolean
}

/**
 * Deprecated, use the default export instead.
 *
 * @category deprecated
 * @deprecated
 * @since 1.0.0
 */
export const reporter = <T>(
  validation: t.Validation<T>,
  options?: ReporterOptions,
) =>
  pipe(
    validation,
    E.mapLeft((errors) => formatValidationErrors(errors, options)),
    E.fold(
      (errors) => errors,
      () => [],
    ),
  )

interface PrettyReporter extends Reporter<string[]> {
  report: <T>(
    validation: t.Validation<T>,
    options?: ReporterOptions,
  ) => string[]
}

const prettyReporter: PrettyReporter = {report: reporter}
export default prettyReporter