1 files changed, 997 insertions, 0 deletions

diff --git a/src/data/validators.js b/src/data/validators.js
new file mode 100644
index 0000000..987f806
--- /dev/null
+++ b/src/data/validators.js
@@ -0,0 +1,997 @@
+import {inspect as nodeInspect} from 'node:util';
+
+import {openAggregate, withAggregate} from '#aggregate';
+import {colors, ENABLE_COLOR} from '#cli';
+import {cut, empty, matchMultiline, typeAppearance} from '#sugar';
+import {commentaryRegexCaseInsensitive, commentaryRegexCaseSensitiveOneShot}
+  from '#wiki-data';
+
+function inspect(value) {
+  return nodeInspect(value, {colors: ENABLE_COLOR});
+}
+
+export function getValidatorCreator(validator) {
+  return validator[Symbol.for(`hsmusic.validator.creator`)] ?? null;
+}
+
+export function getValidatorCreatorMeta(validator) {
+  return validator[Symbol.for(`hsmusic.validator.creatorMeta`)] ?? null;
+}
+
+export function setValidatorCreatorMeta(validator, creator, meta) {
+  validator[Symbol.for(`hsmusic.validator.creator`)] = creator;
+  validator[Symbol.for(`hsmusic.validator.creatorMeta`)] = meta;
+  return validator;
+}
+
+// Basic types (primitives)
+
+export function a(noun) {
+  return /[aeiou]/.test(noun[0]) ? `an ${noun}` : `a ${noun}`;
+}
+
+export function validateType(type) {
+  const fn = value => {
+    if (typeof value !== type)
+      throw new TypeError(`Expected ${a(type)}, got ${typeAppearance(value)}`);
+
+    return true;
+  };
+
+  setValidatorCreatorMeta(fn, validateType, {type});
+
+  return fn;
+}
+
+export const isBoolean =
+  validateType('boolean');
+
+export const isFunction =
+  validateType('function');
+
+export const isNumber =
+  validateType('number');
+
+export const isString =
+  validateType('string');
+
+export const isSymbol =
+  validateType('symbol');
+
+// Use isObject instead, which disallows null.
+export const isTypeofObject =
+  validateType('object');
+
+export function isPositive(number) {
+  isNumber(number);
+
+  if (number <= 0) throw new TypeError(`Expected positive number`);
+
+  return true;
+}
+
+export function isNegative(number) {
+  isNumber(number);
+
+  if (number >= 0) throw new TypeError(`Expected negative number`);
+
+  return true;
+}
+
+export function isPositiveOrZero(number) {
+  isNumber(number);
+
+  if (number < 0) throw new TypeError(`Expected positive number or zero`);
+
+  return true;
+}
+
+export function isNegativeOrZero(number) {
+  isNumber(number);
+
+  if (number > 0) throw new TypeError(`Expected negative number or zero`);
+
+  return true;
+}
+
+export function isInteger(number) {
+  isNumber(number);
+
+  if (number % 1 !== 0) throw new TypeError(`Expected integer`);
+
+  return true;
+}
+
+export function isCountingNumber(number) {
+  isInteger(number);
+  isPositive(number);
+
+  return true;
+}
+
+export function isWholeNumber(number) {
+  isInteger(number);
+  isPositiveOrZero(number);
+
+  return true;
+}
+
+export function isStringNonEmpty(value) {
+  isString(value);
+
+  if (value.trim().length === 0)
+    throw new TypeError(`Expected non-empty string`);
+
+  return true;
+}
+
+export function optional(validator) {
+  return value =>
+    value === null ||
+    value === undefined ||
+    validator(value);
+}
+
+// Complex types (non-primitives)
+
+export function isInstance(value, constructor) {
+  isObject(value);
+
+  if (!(value instanceof constructor))
+    throw new TypeError(`Expected ${constructor.name}, got ${value.constructor.name}`);
+
+  return true;
+}
+
+export function isDate(value) {
+  isInstance(value, Date);
+
+  if (isNaN(value))
+    throw new TypeError(`Expected valid date`);
+
+  return true;
+}
+
+export function isObject(value) {
+  isTypeofObject(value);
+
+  // Note: Please remember that null is always a valid value for properties
+  // held by a CacheableObject. This assertion is exclusively for use in other
+  // contexts.
+  if (value === null)
+    throw new TypeError(`Expected an object, got null`);
+
+  return true;
+}
+
+export function isArray(value) {
+  if (typeof value !== 'object' || value === null || !Array.isArray(value))
+    throw new TypeError(`Expected an array, got ${typeAppearance(value)}`);
+
+  return true;
+}
+
+// This one's shaped a bit different from other "is" functions.
+// More like validate functions, it returns a function.
+export function is(...values) {
+  if (Array.isArray(values)) {
+    values = new Set(values);
+  }
+
+  if (values.size === 1) {
+    const expected = Array.from(values)[0];
+
+    return (value) => {
+      if (value !== expected) {
+        throw new TypeError(`Expected ${expected}, got ${value}`);
+      }
+
+      return true;
+    };
+  }
+
+  const fn = (value) => {
+    if (!values.has(value)) {
+      throw new TypeError(`Expected one of ${Array.from(values).join(' ')}, got ${value}`);
+    }
+
+    return true;
+  };
+
+  setValidatorCreatorMeta(fn, is, {values});
+
+  return fn;
+}
+
+function validateArrayItemsHelper(itemValidator) {
+  return (item, index, array) => {
+    try {
+      const value = itemValidator(item, index, array);
+
+      if (value !== true) {
+        throw new Error(`Expected validator to return true`);
+      }
+    } catch (caughtError) {
+      const indexPart = colors.yellow(`zero-index ${index}`)
+      const itemPart = inspect(item);
+      const message = `Error at ${indexPart}: ${itemPart}`;
+      const error = new Error(message, {cause: caughtError});
+      error[Symbol.for('hsmusic.annotateError.indexInSourceArray')] = index;
+      throw error;
+    }
+  };
+}
+
+export function validateArrayItems(itemValidator) {
+  const helper = validateArrayItemsHelper(itemValidator);
+
+  return (array) => {
+    isArray(array);
+
+    withAggregate({message: 'Errors validating array items'}, ({call}) => {
+      for (let index = 0; index < array.length; index++) {
+        call(helper, array[index], index, array);
+      }
+    });
+
+    return true;
+  };
+}
+
+export function strictArrayOf(itemValidator) {
+  return validateArrayItems(itemValidator);
+}
+
+export function sparseArrayOf(itemValidator) {
+  return validateArrayItems((item, index, array) => {
+    if (item === false || item === null) {
+      return true;
+    }
+
+    return itemValidator(item, index, array);
+  });
+}
+
+export function looseArrayOf(itemValidator) {
+  return validateArrayItems((item, index, array) => {
+    if (item === false || item === null || item === undefined) {
+      return true;
+    }
+
+    return itemValidator(item, index, array);
+  });
+}
+
+export function validateInstanceOf(constructor) {
+  const fn = (object) => isInstance(object, constructor);
+
+  setValidatorCreatorMeta(fn, validateInstanceOf, {constructor});
+
+  return fn;
+}
+
+// Wiki data (primitives & non-primitives)
+
+export function isColor(color) {
+  isStringNonEmpty(color);
+
+  if (color.startsWith('#')) {
+    if (![4, 5, 7, 9].includes(color.length))
+      throw new TypeError(`Expected #rgb, #rgba, #rrggbb, or #rrggbbaa, got length ${color.length}`);
+
+    if (/[^0-9a-fA-F]/.test(color.slice(1)))
+      throw new TypeError(`Expected hexadecimal digits`);
+
+    return true;
+  }
+
+  throw new TypeError(`Unknown color format`);
+}
+
+export function isCommentary(commentaryText) {
+  isContentString(commentaryText);
+
+  const rawMatches =
+    Array.from(commentaryText.matchAll(commentaryRegexCaseInsensitive));
+
+  if (empty(rawMatches)) {
+    throw new TypeError(`Expected at least one commentary heading`);
+  }
+
+  const niceMatches =
+    rawMatches.map(match => ({
+      position: match.index,
+      length: match[0].length,
+    }));
+
+  validateArrayItems(({position, length}, index) => {
+    if (index === 0 && position > 0) {
+      throw new TypeError(`Expected first commentary heading to be at top`);
+    }
+
+    const ownInput = commentaryText.slice(position, position + length);
+    const restOfInput = commentaryText.slice(position + length);
+
+    const upToNextLineBreak =
+      (restOfInput.includes('\n')
+        ? restOfInput.slice(0, restOfInput.indexOf('\n'))
+        : restOfInput);
+
+    if (/\S/.test(upToNextLineBreak)) {
+      throw new TypeError(
+        `Expected commentary heading to occupy entire line, got extra text:\n` +
+        `${colors.green(`"${cut(ownInput, 40)}"`)} (<- heading)\n` +
+        `(extra on same line ->) ${colors.red(`"${cut(upToNextLineBreak, 30)}"`)}\n` +
+        `(Check for missing "|-" in YAML, or a misshapen annotation)`);
+    }
+
+    if (!commentaryRegexCaseSensitiveOneShot.test(ownInput)) {
+      throw new TypeError(
+        `Miscapitalization in commentary heading:\n` +
+        `${colors.red(`"${cut(ownInput, 60)}"`)}\n` +
+        `(Check for ${colors.red(`"<I>"`)} instead of ${colors.green(`"<i>"`)})`);
+    }
+
+    const nextHeading =
+      (index === niceMatches.length - 1
+        ? commentaryText.length
+        : niceMatches[index + 1].position);
+
+    const upToNextHeading =
+      commentaryText.slice(position + length, nextHeading);
+
+    if (!/\S/.test(upToNextHeading)) {
+      throw new TypeError(
+        `Expected commentary entry to have body text, only got a heading`);
+    }
+
+    return true;
+  })(niceMatches);
+
+  return true;
+}
+
+const isArtistRef = validateReference('artist');
+
+export function validateProperties(spec) {
+  const {
+    [validateProperties.validateOtherKeys]: validateOtherKeys = null,
+    [validateProperties.allowOtherKeys]: allowOtherKeys = false,
+  } = spec;
+
+  const specEntries = Object.entries(spec);
+  const specKeys = Object.keys(spec);
+
+  return (object) => {
+    isObject(object);
+
+    if (Array.isArray(object))
+      throw new TypeError(`Expected an object, got array`);
+
+    withAggregate({message: `Errors validating object properties`}, ({push}) => {
+      const testEntries = specEntries.slice();
+
+      const unknownKeys = Object.keys(object).filter((key) => !specKeys.includes(key));
+      if (validateOtherKeys) {
+        for (const key of unknownKeys) {
+          testEntries.push([key, validateOtherKeys]);
+        }
+      }
+
+      for (const [specKey, specValidator] of testEntries) {
+        const value = object[specKey];
+        try {
+          specValidator(value);
+        } catch (caughtError) {
+          const keyPart = colors.green(specKey);
+          const valuePart = inspect(value);
+          const message = `Error for key ${keyPart}: ${valuePart}`;
+          push(new Error(message, {cause: caughtError}));
+        }
+      }
+
+      if (!validateOtherKeys && !allowOtherKeys && !empty(unknownKeys)) {
+        push(new Error(
+          `Unknown keys present (${unknownKeys.length}): [${unknownKeys.join(', ')}]`));
+      }
+    });
+
+    return true;
+  };
+}
+
+validateProperties.validateOtherKeys = Symbol();
+validateProperties.allowOtherKeys = Symbol();
+
+export const validateAllPropertyValues = (validator) =>
+  validateProperties({
+    [validateProperties.validateOtherKeys]: validator,
+  });
+
+const illeaglInvisibleSpace = {
+  action: 'delete',
+};
+
+const illegalVisibleSpace = {
+  action: 'replace',
+  with: ' ',
+  withAnnotation: `normal space`,
+};
+
+const illegalContentSpec = [
+  {illegal: '\u200b', annotation: `zero-width space`, ...illeaglInvisibleSpace},
+  {illegal: '\u2005', annotation: `four-per-em space`, ...illegalVisibleSpace},
+  {illegal: '\u205f', annotation: `medium mathematical space`, ...illegalVisibleSpace},
+  {illegal: '\xa0', annotation: `non-breaking space`, ...illegalVisibleSpace},
+
+  {
+    action: 'replace',
+    illegal: '<a href',
+    annotation: `HTML-style link`,
+    with: '[...](...)',
+    withAnnotation: `markdown`,
+  },
+];
+
+for (const entry of illegalContentSpec) {
+  entry.test = string =>
+    string.startsWith(entry.illegal);
+
+  if (entry.action === 'replace') {
+    entry.enact = string =>
+      string.replaceAll(entry.illegal, entry.with);
+  }
+}
+
+const illegalContentRegexp =
+  new RegExp(
+    illegalContentSpec
+      .map(entry => entry.illegal)
+      .map(illegal => `${illegal}+`)
+      .join('|'),
+    'g');
+
+const illegalCharactersInContent =
+  illegalContentSpec
+    .map(entry => entry.illegal)
+    .join('');
+
+const legalContentNearEndRegexp =
+  new RegExp(`[^\n${illegalCharactersInContent}]+$`);
+
+const legalContentNearStartRegexp =
+  new RegExp(`^[^\n${illegalCharactersInContent}]+`);
+
+const trimWhitespaceNearBothSidesRegexp =
+  /^ +| +$/gm;
+
+const trimWhitespaceNearEndRegexp =
+  / +$/gm;
+
+export function isContentString(content) {
+  isStringNonEmpty(content);
+
+  const mainAggregate = openAggregate({
+    message: `Errors validating content string`,
+    translucent: 'single',
+  });
+
+  const illegalAggregate = openAggregate({
+    message: `Illegal characters found in content string`,
+  });
+
+  for (const {match, where} of matchMultiline(content, illegalContentRegexp)) {
+    const {annotation, action, ...options} =
+      illegalContentSpec
+        .find(entry => entry.test(match[0]));
+
+    const matchStart = match.index;
+    const matchEnd = match.index + match[0].length;
+
+    const before =
+      content
+        .slice(Math.max(0, matchStart - 3), matchStart)
+        .match(legalContentNearEndRegexp)
+        ?.[0];
+
+    const after =
+      content
+        .slice(matchEnd, Math.min(content.length, matchEnd + 3))
+        .match(legalContentNearStartRegexp)
+        ?.[0];
+
+    const beforePart =
+      before && `"${before}"`;
+
+    const afterPart =
+      after && `"${after}"`;
+
+    const surroundings =
+      (before && after
+        ? `between ${beforePart} and ${afterPart}`
+     : before
+        ? `after ${beforePart}`
+     : after
+        ? `before ${afterPart}`
+        : ``);
+
+    const illegalPart =
+      colors.red(
+        (annotation
+          ? `"${match[0]}" (${annotation})`
+          : `"${match[0]}"`));
+
+    const replacement =
+      (action === 'replace'
+        ? options.enact(match[0])
+        : null);
+
+    const replaceWithPart =
+      (action === 'replace'
+        ? colors.green(
+            (options.withAnnotation
+              ? `"${replacement}" (${options.withAnnotation})`
+              : `"${replacement}"`))
+        : null);
+
+    const actionPart =
+      (action === `delete`
+        ? `Delete ${illegalPart}`
+     : action === 'replace'
+        ? `Replace ${illegalPart} with ${replaceWithPart}`
+        : `Matched ${illegalPart}`);
+
+    const parts = [
+      actionPart,
+      surroundings,
+      `(${where})`,
+    ].filter(Boolean);
+
+    illegalAggregate.push(new TypeError(parts.join(` `)));
+  }
+
+  const isMultiline = content.includes('\n');
+
+  const trimWhitespaceAggregate = openAggregate({
+    message:
+      (isMultiline
+        ? `Whitespace found at end of line`
+        : `Whitespace found at start or end`),
+  });
+
+  const trimWhitespaceRegexp =
+    (isMultiline
+      ? trimWhitespaceNearEndRegexp
+      : trimWhitespaceNearBothSidesRegexp);
+
+  for (
+    const {match, lineNumber, columnNumber, containingLine} of
+    matchMultiline(content, trimWhitespaceRegexp, {
+      formatWhere: false,
+      getContainingLine: true,
+    })
+  ) {
+    const linePart =
+      colors.yellow(`line ${lineNumber + 1}`);
+
+    const where =
+      (match[0].length === containingLine.length
+        ? `as all of ${linePart}`
+     : columnNumber === 0
+        ? (isMultiline
+            ? `at start of ${linePart}`
+            : `at start`)
+        : (isMultiline
+            ? `at end of ${linePart}`
+            : `at end`));
+
+    const whitespacePart =
+      colors.red(`"${match[0]}"`);
+
+    const parts = [
+      `Matched ${whitespacePart}`,
+      where,
+    ];
+
+    trimWhitespaceAggregate.push(new TypeError(parts.join(` `)));
+  }
+
+  mainAggregate.call(() => illegalAggregate.close());
+  mainAggregate.call(() => trimWhitespaceAggregate.close());
+  mainAggregate.close();
+
+  return true;
+}
+
+export function isThingClass(thingClass) {
+  isFunction(thingClass);
+
+  if (!Object.hasOwn(thingClass, Symbol.for('Thing.referenceType'))) {
+    throw new TypeError(`Expected a Thing constructor, missing Thing.referenceType`);
+  }
+
+  return true;
+}
+
+export const isContribution = validateProperties({
+  who: isArtistRef,
+  what: optional(isStringNonEmpty),
+});
+
+export const isContributionList = validateArrayItems(isContribution);
+
+export const isAdditionalFile = validateProperties({
+  title: isName,
+  description: optional(isContentString),
+  files: optional(validateArrayItems(isString)),
+});
+
+export const isAdditionalFileList = validateArrayItems(isAdditionalFile);
+
+export const isTrackSection = validateProperties({
+  name: optional(isName),
+  color: optional(isColor),
+  dateOriginallyReleased: optional(isDate),
+  isDefaultTrackSection: optional(isBoolean),
+  tracks: optional(validateReferenceList('track')),
+});
+
+export const isTrackSectionList = validateArrayItems(isTrackSection);
+
+export function isDimensions(dimensions) {
+  isArray(dimensions);
+
+  if (dimensions.length !== 2) throw new TypeError(`Expected 2 item array`);
+
+  if (dimensions[0] !== null) {
+    isPositive(dimensions[0]);
+    isInteger(dimensions[0]);
+  }
+
+  if (dimensions[1] !== null) {
+    isPositive(dimensions[1]);
+    isInteger(dimensions[1]);
+  }
+
+  return true;
+}
+
+export function isDirectory(directory) {
+  isStringNonEmpty(directory);
+
+  if (directory.match(/[^a-zA-Z0-9_-]/))
+    throw new TypeError(`Expected only letters, numbers, dash, and underscore, got "${directory}"`);
+
+  return true;
+}
+
+export function isDuration(duration) {
+  isNumber(duration);
+  isPositiveOrZero(duration);
+
+  return true;
+}
+
+export function isFileExtension(string) {
+  isStringNonEmpty(string);
+
+  if (string[0] === '.')
+    throw new TypeError(`Expected no dot (.) at the start of file extension`);
+
+  if (string.match(/[^a-zA-Z0-9_]/))
+    throw new TypeError(`Expected only alphanumeric and underscore`);
+
+  return true;
+}
+
+export function isLanguageCode(string) {
+  // TODO: This is a stub function because really we don't need a detailed
+  // is-language-code parser right now.
+
+  isString(string);
+
+  return true;
+}
+
+export function isName(name) {
+  return isContentString(name);
+}
+
+export function isURL(string) {
+  isStringNonEmpty(string);
+
+  new URL(string);
+
+  return true;
+}
+
+export function validateReference(type = 'track') {
+  return (ref) => {
+    isStringNonEmpty(ref);
+
+    const match = ref
+      .trim()
+      .match(/^(?:(?<typePart>\S+):(?=\S))?(?<directoryPart>.+)(?<!:)$/);
+
+    if (!match) throw new TypeError(`Malformed reference`);
+
+    const {groups: {typePart, directoryPart}} = match;
+
+    if (typePart) {
+      if (typePart !== type)
+        throw new TypeError(`Expected ref to begin with "${type}:", got "${typePart}:"`);
+
+      isDirectory(directoryPart);
+    }
+
+    isName(ref);
+
+    return true;
+  };
+}
+
+export function validateReferenceList(type = '') {
+  return validateArrayItems(validateReference(type));
+}
+
+const validateWikiData_cache = {};
+
+export function validateWikiData({
+  referenceType = '',
+  allowMixedTypes = false,
+}) {
+  if (referenceType && allowMixedTypes) {
+    throw new TypeError(`Don't specify both referenceType and allowMixedTypes`);
+  }
+
+  validateWikiData_cache[referenceType] ??= {};
+  validateWikiData_cache[referenceType][allowMixedTypes] ??= new WeakMap();
+
+  const isArrayOfObjects = validateArrayItems(isObject);
+
+  return (array) => {
+    const subcache = validateWikiData_cache[referenceType][allowMixedTypes];
+    if (subcache.has(array)) return subcache.get(array);
+
+    let OK = false;
+
+    try {
+      isArrayOfObjects(array);
+
+      if (empty(array)) {
+        OK = true; return true;
+      }
+
+      const allRefTypes = new Set();
+
+      let foundThing = false;
+      let foundOtherObject = false;
+
+      for (const object of array) {
+        const {[Symbol.for('Thing.referenceType')]: referenceType} = object.constructor;
+
+        if (referenceType === undefined) {
+          foundOtherObject = true;
+
+          // Early-exit if a Thing has been found - nothing more can be learned.
+          if (foundThing) {
+            throw new TypeError(`Expected array of wiki data objects, got mixed items`);
+          }
+        } else {
+          foundThing = true;
+
+          // Early-exit if a non-Thing object has been found - nothing more can
+          // be learned.
+          if (foundOtherObject) {
+            throw new TypeError(`Expected array of wiki data objects, got mixed items`);
+          }
+
+          allRefTypes.add(referenceType);
+        }
+      }
+
+      if (foundOtherObject && !foundThing) {
+        throw new TypeError(`Expected array of wiki data objects, got array of other objects`);
+      }
+
+      if (allRefTypes.size > 1) {
+        if (allowMixedTypes) {
+          OK = true; return true;
+        }
+
+        const types = () => Array.from(allRefTypes).join(', ');
+
+        if (referenceType) {
+          if (allRefTypes.has(referenceType)) {
+            allRefTypes.remove(referenceType);
+            throw new TypeError(`Expected array of only ${referenceType}, also got other types: ${types()}`)
+          } else {
+            throw new TypeError(`Expected array of only ${referenceType}, got other types: ${types()}`);
+          }
+        }
+
+        throw new TypeError(`Expected array of unmixed reference types, got multiple: ${types()}`);
+      }
+
+      const onlyRefType = Array.from(allRefTypes)[0];
+
+      if (referenceType && onlyRefType !== referenceType) {
+        throw new TypeError(`Expected array of ${referenceType}, got array of ${onlyRefType}`)
+      }
+
+      OK = true; return true;
+    } finally {
+      subcache.set(array, OK);
+    }
+  };
+}
+
+export const isAdditionalName = validateProperties({
+  name: isName,
+  annotation: optional(isContentString),
+
+  // TODO: This only allows indicating sourcing from a track.
+  // That's okay for the current limited use of "from", but
+  // could be expanded later.
+  from:
+    // Double TODO: Explicitly allowing both references and
+    // live objects to co-exist is definitely weird, and
+    // altogether questions the way we define validators...
+    optional(anyOf(
+      validateReferenceList('track'),
+      validateWikiData({referenceType: 'track'}))),
+});
+
+export const isAdditionalNameList = validateArrayItems(isAdditionalName);
+
+// Compositional utilities
+
+export function anyOf(...validators) {
+  const validConstants = new Set();
+  const validConstructors = new Set();
+  const validTypes = new Set();
+
+  const constantValidators = [];
+  const constructorValidators = [];
+  const typeValidators = [];
+
+  const leftoverValidators = [];
+
+  for (const validator of validators) {
+    const creator = getValidatorCreator(validator);
+    const creatorMeta = getValidatorCreatorMeta(validator);
+
+    switch (creator) {
+      case is:
+        for (const value of creatorMeta.values) {
+          validConstants.add(value);
+        }
+
+        constantValidators.push(validator);
+        break;
+
+      case validateInstanceOf:
+        validConstructors.add(creatorMeta.constructor);
+        constructorValidators.push(validator);
+        break;
+
+      case validateType:
+        validTypes.add(creatorMeta.type);
+        typeValidators.push(validator);
+        break;
+
+      default:
+        leftoverValidators.push(validator);
+        break;
+    }
+  }
+
+  return (value) => {
+    const errorInfo = [];
+
+    if (validConstants.has(value)) {
+      return true;
+    }
+
+    if (!empty(validTypes)) {
+      if (validTypes.has(typeof value)) {
+        return true;
+      }
+    }
+
+    for (const constructor of validConstructors) {
+      if (value instanceof constructor) {
+        return true;
+      }
+    }
+
+    for (const [i, validator] of leftoverValidators.entries()) {
+      try {
+        const result = validator(value);
+
+        if (result !== true) {
+          throw new Error(`Check returned false`);
+        }
+
+        return true;
+      } catch (error) {
+        errorInfo.push([validator, i, error]);
+      }
+    }
+
+    // Don't process error messages until every validator has failed.
+
+    const errors = [];
+    const prefaceErrorInfo = [];
+
+    let offset = 0;
+
+    if (!empty(validConstants)) {
+      const constants =
+        Array.from(validConstants);
+
+      const gotPart = `, got ${value}`;
+
+      prefaceErrorInfo.push([
+        constantValidators,
+        offset++,
+        new TypeError(
+          `Expected any of ${constants.join(' ')}` + gotPart),
+      ]);
+    }
+
+    if (!empty(validTypes)) {
+      const types =
+        Array.from(validTypes);
+
+      const gotType = typeAppearance(value);
+      const gotPart = `, got ${gotType}`;
+
+      prefaceErrorInfo.push([
+        typeValidators,
+        offset++,
+        new TypeError(
+          `Expected any of ${types.join(', ')}` + gotPart),
+      ]);
+    }
+
+    if (!empty(validConstructors)) {
+      const names =
+        Array.from(validConstructors)
+          .map(constructor => constructor.name);
+
+      const gotName = value?.constructor?.name;
+      const gotPart = (gotName ? `, got ${gotName}` : ``);
+
+      prefaceErrorInfo.push([
+        constructorValidators,
+        offset++,
+        new TypeError(
+          `Expected any of ${names.join(', ')}` + gotPart),
+      ]);
+    }
+
+    for (const info of errorInfo) {
+      info[1] += offset;
+    }
+
+    for (const [validator, i, error] of prefaceErrorInfo.concat(errorInfo)) {
+      error.message =
+        (validator?.name
+          ? `${i + 1}. "${validator.name}": ${error.message}`
+          : `${i + 1}. ${error.message}`);
+
+      error.check =
+        (Array.isArray(validator) && validator.length === 1
+          ? validator[0]
+          : validator);
+
+      errors.push(error);
+    }
+
+    const total = offset + leftoverValidators.length;
+    throw new AggregateError(errors,
+      `Expected any of ${total} possible checks, ` +
+      `but none were true`);
+  };
+}