new rule exports valid

Author: mightyiam

src/rules/exports-valid.js

@@ -0,0 +1,162 @@
+const isPlainObj = require('is-plain-obj');
+const LintIssue = require('../LintIssue');
+const {exists} = require('../validators/property');
+
+const lintId = 'exports-valid';
+const nodeName = 'exports';
+const ruleType = 'standard';
+
+const isValidPathKey = (key) => key.startsWith('.') || key.startsWith('./');
+
+const isValidPath = (value) => value.startsWith('./');
+
+const validateFallbacks = (fallbacks) => {
+  if (fallbacks.length === 0) return {error: 'fallbackEmpty'};
+
+  const {validIndexes, invalidIndexes, hasNonString, invalidFollowingValid} = fallbacks.reduce(
+    (acc, cur, i) => {
+      if (typeof cur === 'string') {
+        const isValid = isValidPath(cur);
+
+        acc[isValid ? 'validIndexes' : 'invalidIndexes'].push(i);
+        if (!isValid && acc.validIndexes.length) {
+          acc.invalidFollowingValid = true;
+        }
+      } else {
+        acc.hasNonString = true;
+      }
+
+      return acc;
+    },
+    {validIndexes: [], invalidIndexes: [], hasNonString: false}
+  );
+
+  if (validIndexes.length === 0) {
+    return {error: 'fallbackNoValidPath'};
+  }
+
+  if (invalidIndexes.length === 0) {
+    return {error: 'fallbackNoInvalids'};
+  }
+
+  if (validIndexes.length > 1) {
+    return {error: 'fallbackUnreachableValid'};
+  }
+
+  if (invalidFollowingValid) {
+    return {error: 'fallbackUnreachableInvalid'};
+  }
+
+  if (hasNonString) {
+    return {error: 'fallbackHasNonString'};
+  }
+
+  return true;
+};
+
+// eslint-disable-next-line max-lines-per-function
+const lint = (packageJsonData, severity, config = {conditions: []}) => {
+  const conditions = [...(config.conditions || []), 'default'];
+
+  if (!exists(packageJsonData, nodeName)) return true;
+
+  // eslint-disable-next-line complexity,max-statements,max-lines-per-function
+  const traverse = (parentKey, parentType, exports) => {
+    if (typeof exports === 'string') {
+      if (!isValidPath(exports)) {
+        return {error: 'invalidPath', str: exports};
+      }
+
+      if (parentKey.endsWith('/') && !exports.endsWith('/')) {
+        return {error: 'folderMappedToFile', str: parentKey};
+      }
+
+      return true;
+    }
+
+    if (Array.isArray(exports)) {
+      // https://nodejs.org/api/esm.html#esm_package_exports_fallbacks
+      // eslint-disable-next-line no-restricted-syntax
+      return validateFallbacks(exports);
+    }
+
+    if (!isPlainObj(exports)) {
+      return {error: 'unexpectedType', str: typeof exports};
+    }
+
+    // either a paths object or a conditions object
+    let objectType;
+
+    const entries = Object.entries(exports);
+
+    for (let i = 0; i < entries.length; i += 1) {
+      const [key, value] = entries[i];
+
+      if (isValidPathKey(key)) {
+        if (objectType === 'conditions') {
+          return {error: 'pathInConditions', str: key};
+        }
+
+        if (parentType === 'paths') {
+          return {error: 'nestedPaths', str: parentKey};
+        }
+
+        objectType = 'paths';
+
+        const result = traverse(key, objectType, value);
+
+        if (result !== true) return result;
+      } else {
+        // `key` interpreted as a condition
+        if (!conditions.includes(key)) {
+          return {error: 'unsupportedCondition', str: key};
+        }
+
+        if (objectType === 'paths') {
+          return {error: 'conditionInPaths', str: key};
+        }
+
+        objectType = 'conditions';
+        if (key === 'default' && i + 1 < entries.length) {
+          return {error: 'defaultConditionNotLast'};
+        }
+
+        const result = traverse(key, objectType, value);
+
+        if (result !== true) return result;
+      }
+    }
+
+    return true;
+  };
+
+  const result = traverse(nodeName, 'root', packageJsonData[nodeName]);
+
+  if (result !== true) {
+    const message = {
+      invalidPath: `invalid path \`${result.str}\` must start with \`./\``,
+      pathInConditions: `found path key \`${result.str}\` in a conditions object`,
+      nestedPaths: `key \`${result.str}\` has paths object vaule but only conditions may be nested`,
+      unsupportedCondition: `condition \`${result.str}\` not in supported conditions \`${conditions}\``,
+      conditionInPaths: `found condition key \`${result.str}\` in a paths object`,
+      unexpectedType: `unexpected \`${result.str}\``,
+      defaultConditionNotLast: 'condition `default` must be the last key',
+      folderMappedToFile: `the value of the folder mapping key \`${result.str}\` must end with \`/\``,
+      fallbackEmpty: 'empty fallback array',
+      fallbackNoValidPath: 'fallback array has no valid path',
+      fallbackNoInvalids: 'fallback array has no invalid values',
+      fallbackUnreachableValid: 'fallback array has multiple valid paths',
+      fallbackUnreachableInvalid: 'found invalid value following a valid path',
+      fallbackHasNonString: 'fallback array must have only strings',
+    }[result.error];
+
+    return new LintIssue(lintId, severity, nodeName, message);
+  }
+
+  return true;
+};
+
+module.exports = {
+  lint,
+  ruleType,
+};