space-before-function-paren.ts

import {
  AST_NODE_TYPES,
  TSESTree,
} from '@typescript-eslint/experimental-utils';
import { isOpeningParenToken } from 'eslint-utils';
import * as util from '../util';

type Option = 'never' | 'always';
type FuncOption = Option | 'ignore';

export type Options = [
  | Option
  | Partial<{
      anonymous: FuncOption;
      named: FuncOption;
      asyncArrow: FuncOption;
    }>,
];
export type MessageIds = 'unexpected' | 'missing';

export default util.createRule<Options, MessageIds>({
  name: 'space-before-function-paren',
  meta: {
    type: 'layout',
    docs: {
      description:
        'enforce consistent spacing before `function` definition opening parenthesis',
      category: 'Stylistic Issues',
      recommended: false,
    },
    fixable: 'whitespace',
    schema: [
      {
        oneOf: [
          {
            enum: ['always', 'never'],
          },
          {
            type: 'object',
            properties: {
              anonymous: {
                enum: ['always', 'never', 'ignore'],
              },
              named: {
                enum: ['always', 'never', 'ignore'],
              },
              asyncArrow: {
                enum: ['always', 'never', 'ignore'],
              },
            },
            additionalProperties: false,
          },
        ],
      },
    ],
    messages: {
      unexpected: 'Unexpected space before function parentheses.',
      missing: 'Missing space before function parentheses.',
    },
  },
  defaultOptions: ['always'],

  create(context) {
    const sourceCode = context.getSourceCode();
    const baseConfig =
      typeof context.options[0] === 'string' ? context.options[0] : 'always';
    const overrideConfig =
      typeof context.options[0] === 'object' ? context.options[0] : {};

    /**
     * Determines whether a function has a name.
     * @param {ASTNode} node The function node.
     * @returns {boolean} Whether the function has a name.
     */
    function isNamedFunction(
      node:
        | TSESTree.ArrowFunctionExpression
        | TSESTree.FunctionDeclaration
        | TSESTree.FunctionExpression,
    ): boolean {
      if (node.id) {
        return true;
      }

      const parent = node.parent!;

      return (
        parent.type === AST_NODE_TYPES.MethodDefinition ||
        (parent.type === AST_NODE_TYPES.Property &&
          (parent.kind === 'get' || parent.kind === 'set' || parent.method))
      );
    }

    /**
     * Gets the config for a given function
     * @param {ASTNode} node The function node
     * @returns {string} "always", "never", or "ignore"
     */
    function getConfigForFunction(
      node:
        | TSESTree.ArrowFunctionExpression
        | TSESTree.FunctionDeclaration
        | TSESTree.FunctionExpression,
    ): FuncOption {
      if (node.type === AST_NODE_TYPES.ArrowFunctionExpression) {
        // Always ignore non-async functions and arrow functions without parens, e.g. async foo => bar
        if (
          node.async &&
          isOpeningParenToken(sourceCode.getFirstToken(node, { skip: 1 })!)
        ) {
          return overrideConfig.asyncArrow ?? baseConfig;
        }
      } else if (isNamedFunction(node)) {
        return overrideConfig.named ?? baseConfig;

        // `generator-star-spacing` should warn anonymous generators. E.g. `function* () {}`
      } else if (!node.generator) {
        return overrideConfig.anonymous ?? baseConfig;
      }

      return 'ignore';
    }

    /**
     * Checks the parens of a function node
     * @param {ASTNode} node A function node
     * @returns {void}
     */
    function checkFunction(
      node:
        | TSESTree.ArrowFunctionExpression
        | TSESTree.FunctionDeclaration
        | TSESTree.FunctionExpression,
    ): void {
      const functionConfig = getConfigForFunction(node);

      if (functionConfig === 'ignore') {
        return;
      }

      let leftToken: TSESTree.Token, rightToken: TSESTree.Token;
      if (node.typeParameters) {
        leftToken = sourceCode.getLastToken(node.typeParameters)!;
        rightToken = sourceCode.getTokenAfter(leftToken)!;
      } else {
        rightToken = sourceCode.getFirstToken(node, isOpeningParenToken)!;
        leftToken = sourceCode.getTokenBefore(rightToken)!;
      }
      const hasSpacing = sourceCode.isSpaceBetweenTokens(leftToken, rightToken);

      if (hasSpacing && functionConfig === 'never') {
        context.report({
          node,
          loc: leftToken.loc.end,
          messageId: 'unexpected',
          fix: fixer =>
            fixer.removeRange([leftToken.range[1], rightToken.range[0]]),
        });
      } else if (
        !hasSpacing &&
        functionConfig === 'always' &&
        (!node.typeParameters || node.id)
      ) {
        context.report({
          node,
          loc: leftToken.loc.end,
          messageId: 'missing',
          fix: fixer => fixer.insertTextAfter(leftToken, ' '),
        });
      }
    }

    return {
      ArrowFunctionExpression: checkFunction,
      FunctionDeclaration: checkFunction,
      FunctionExpression: checkFunction,
    };
  },
});