group-exports.js

import docsUrl from '../docsUrl';
import values from 'object.values';
import flat from 'array.prototype.flat';

const meta = {
  type: 'suggestion',
  docs: {
    url: docsUrl('group-exports'),
  },
};
/* eslint-disable max-len */
const errors = {
  ExportNamedDeclaration: 'Multiple named export declarations; consolidate all named exports into a single export declaration',
  AssignmentExpression: 'Multiple CommonJS exports; consolidate all exports into a single assignment to `module.exports`',
};
/* eslint-enable max-len */

/**
 * Returns an array with names of the properties in the accessor chain for MemberExpression nodes
 *
 * Example:
 *
 * `module.exports = {}` => ['module', 'exports']
 * `module.exports.property = true` => ['module', 'exports', 'property']
 *
 * @param     {Node}    node    AST Node (MemberExpression)
 * @return    {Array}           Array with the property names in the chain
 * @private
 */
function accessorChain(node) {
  const chain = [];

  do {
    chain.unshift(node.property.name);

    if (node.object.type === 'Identifier') {
      chain.unshift(node.object.name);
      break;
    }

    node = node.object;
  } while (node.type === 'MemberExpression');

  return chain;
}

function create(context) {
  const nodes = {
    modules: {
      set: new Set(),
      sources: {},
    },
    types: {
      set: new Set(),
      sources: {},
    },
    commonjs: {
      set: new Set(),
    },
  };

  return {
    ExportNamedDeclaration(node) {
      const target = node.exportKind === 'type' ? nodes.types : nodes.modules;
      if (!node.source) {
        target.set.add(node);
      } else if (Array.isArray(target.sources[node.source.value])) {
        target.sources[node.source.value].push(node);
      } else {
        target.sources[node.source.value] = [node];
      }
    },

    AssignmentExpression(node) {
      if (node.left.type !== 'MemberExpression') {
        return;
      }

      const chain = accessorChain(node.left);

      // Assignments to module.exports
      // Deeper assignments are ignored since they just modify what's already being exported
      // (ie. module.exports.exported.prop = true is ignored)
      if (chain[0] === 'module' && chain[1] === 'exports' && chain.length <= 3) {
        nodes.commonjs.set.add(node);
        return;
      }

      // Assignments to exports (exports.* = *)
      if (chain[0] === 'exports' && chain.length === 2) {
        nodes.commonjs.set.add(node);
        return;
      }
    },

    'Program:exit': function onExit() {
      // Report multiple `export` declarations (ES2015 modules)
      if (nodes.modules.set.size > 1) {
        nodes.modules.set.forEach(node => {
          context.report({
            node,
            message: errors[node.type],
          });
        });
      }

      // Report multiple `aggregated exports` from the same module (ES2015 modules)
      flat(values(nodes.modules.sources)
        .filter(nodesWithSource => Array.isArray(nodesWithSource) && nodesWithSource.length > 1))
        .forEach((node) => {
          context.report({
            node,
            message: errors[node.type],
          });
        });

      // Report multiple `export type` declarations (FLOW ES2015 modules)
      if (nodes.types.set.size > 1) {
        nodes.types.set.forEach(node => {
          context.report({
            node,
            message: errors[node.type],
          });
        });
      }

      // Report multiple `aggregated type exports` from the same module (FLOW ES2015 modules)
      flat(values(nodes.types.sources)
        .filter(nodesWithSource => Array.isArray(nodesWithSource) && nodesWithSource.length > 1))
        .forEach((node) => {
          context.report({
            node,
            message: errors[node.type],
          });
        });

      // Report multiple `module.exports` assignments (CommonJS)
      if (nodes.commonjs.set.size > 1) {
        nodes.commonjs.set.forEach(node => {
          context.report({
            node,
            message: errors[node.type],
          });
        });
      }
    },
  };
}

module.exports = {
  meta,
  create,
};