prefer-readonly-parameter-types.ts

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

export default util.createRule({
  name: 'prefer-readonly-parameter-types',
  meta: {
    type: 'suggestion',
    docs: {
      description: 'TODO',
      category: 'Possible Errors',
      recommended: false,
      requiresTypeChecking: true,
    },
    schema: [
      {
        type: 'string',
        enum: ['prefer-readonly', 'prefer-mutable', 'ignore'],
      },
    ],
    messages: {
      shouldBeReadonly: 'Parameter should be a read only type',
    },
  },
  defaultOptions: [],
  create(context) {
    const { esTreeNodeToTSNodeMap, program } = util.getParserServices(context);
    const checker = program.getTypeChecker();

    return {
      'ArrowFunctionExpression, FunctionDeclaration, FunctionExpression, TSEmptyBodyFunctionExpression'(
        node:
          | TSESTree.ArrowFunctionExpression
          | TSESTree.FunctionDeclaration
          | TSESTree.FunctionExpression
          | TSESTree.TSEmptyBodyFunctionExpression,
      ): void {
        for (const param of node.params) {
          const actualParam =
            param.type === AST_NODE_TYPES.TSParameterProperty
              ? param.parameter
              : param;
          const tsNode = esTreeNodeToTSNodeMap.get(actualParam);
          const type = checker.getTypeAtLocation(tsNode);
          const isReadOnly = util.isTypeReadonly(checker, type);

          if (!isReadOnly) {
            return context.report({
              node: actualParam,
              messageId: 'shouldBeReadonly',
            });
          }
        }
      },
    };
  },
});