From a1c3759adfd087c8b5c3c892b92885b7dded4224 Mon Sep 17 00:00:00 2001
From: Teddy Katz <teddy.katz@gmail.com>
Date: Fri, 23 Feb 2018 20:30:47 -0500
Subject: [PATCH] Chore: refactor populating configs with defaults in linter
 (#10006)

---
 conf/default-config-options.js                | 29 -----------
 lib/linter.js                                 | 49 +++++++++----------
 .../config-file/js/.eslintrc.parser3.js       |  4 +-
 3 files changed, 23 insertions(+), 59 deletions(-)
 delete mode 100644 conf/default-config-options.js

diff --git a/conf/default-config-options.js b/conf/default-config-options.js
deleted file mode 100644
index 96fe25ce6f1..00000000000
--- a/conf/default-config-options.js
+++ /dev/null
@@ -1,29 +0,0 @@
-/**
- * @fileoverview Default config options
- * @author Teddy Katz
- */
-
-"use strict";
-
-/**
- * Freezes an object and all its nested properties
- * @param {Object} obj The object to deeply freeze
- * @returns {Object} `obj` after freezing it
- */
-function deepFreeze(obj) {
-    if (obj === null || typeof obj !== "object") {
-        return obj;
-    }
-
-    Object.keys(obj).map(key => obj[key]).forEach(deepFreeze);
-    return Object.freeze(obj);
-}
-
-module.exports = deepFreeze({
-    env: {},
-    globals: {},
-    rules: {},
-    settings: {},
-    parser: "espree",
-    parserOptions: {}
-});
diff --git a/lib/linter.js b/lib/linter.js
index 8e95c3a7111..207e2cad081 100755
--- a/lib/linter.js
+++ b/lib/linter.js
@@ -14,7 +14,6 @@ const eslintScope = require("eslint-scope"),
     levn = require("levn"),
     lodash = require("lodash"),
     blankScriptAST = require("../conf/blank-script.json"),
-    defaultConfig = require("../conf/default-config-options.js"),
     CodePathAnalyzer = require("./code-path-analysis/code-path-analyzer"),
     ConfigOps = require("./config/config-ops"),
     validator = require("./config/config-validator"),
@@ -33,6 +32,7 @@ const eslintScope = require("eslint-scope"),
 
 const debug = require("debug")("eslint:linter");
 const MAX_AUTOFIX_PASSES = 10;
+const DEFAULT_PARSER_NAME = "espree";
 
 //------------------------------------------------------------------------------
 // Typedefs
@@ -415,16 +415,13 @@ function normalizeEcmaVersion(ecmaVersion, isModule) {
 }
 
 /**
- * Process initial config to make it safe to extend by file comment config
+ * Populates a config file with the default values, and merges any parserOptions stored in an env into
+ * the parserOptions of the populated config.
  * @param  {Object} config Initial config
  * @param  {Environments} envContext Env context
- * @returns {Object}        Processed config
+ * @returns {Object} Processed config
  */
-function prepareConfig(config, envContext) {
-    config.globals = config.globals || {};
-    const copiedRules = {};
-    let parserOptions = {};
-
+function populateConfig(config, envContext) {
     if (typeof config.rules === "object") {
         Object.keys(config.rules).forEach(k => {
             const rule = config.rules[k];
@@ -432,32 +429,30 @@ function prepareConfig(config, envContext) {
             if (rule === null) {
                 throw new Error(`Invalid config for rule '${k}'.`);
             }
-            if (Array.isArray(rule)) {
-                copiedRules[k] = rule.slice();
-            } else {
-                copiedRules[k] = rule;
-            }
         });
     }
 
     // merge in environment parserOptions
-    if (typeof config.env === "object") {
-        Object.keys(config.env).forEach(envName => {
+    const envNamesEnabledInConfig = typeof config.env === "object"
+        ? Object.keys(config.env).filter(envName => config.env[envName])
+        : [];
+
+    const parserOptionsFromEnv = envNamesEnabledInConfig
+        .reduce((parserOptions, envName) => {
             const env = envContext.get(envName);
 
-            if (config.env[envName] && env && env.parserOptions) {
-                parserOptions = ConfigOps.merge(parserOptions, env.parserOptions);
-            }
-        });
-    }
+            return env && env.parserOptions
+                ? ConfigOps.merge(parserOptions, env.parserOptions)
+                : parserOptions;
+        }, {});
 
     const preparedConfig = {
-        rules: copiedRules,
-        parser: config.parser || defaultConfig.parser,
-        globals: ConfigOps.merge(defaultConfig.globals, config.globals),
-        env: ConfigOps.merge(defaultConfig.env, config.env || {}),
-        settings: ConfigOps.merge(defaultConfig.settings, config.settings || {}),
-        parserOptions: ConfigOps.merge(parserOptions, config.parserOptions || {})
+        rules: config.rules || {},
+        parser: config.parser || DEFAULT_PARSER_NAME,
+        globals: config.globals || {},
+        env: config.env || {},
+        settings: config.settings || {},
+        parserOptions: ConfigOps.merge(parserOptionsFromEnv, config.parserOptions || {})
     };
     const isModule = preparedConfig.parserOptions.sourceType === "module";
 
@@ -810,7 +805,7 @@ module.exports = class Linter {
         }
 
         // process initial config to make it safe to extend
-        config = prepareConfig(config, this.environments);
+        config = populateConfig(config, this.environments);
 
         if (!lastSourceCodes.get(this)) {
 
diff --git a/tests/fixtures/config-file/js/.eslintrc.parser3.js b/tests/fixtures/config-file/js/.eslintrc.parser3.js
index fd5f04ff12e..9324e00652a 100644
--- a/tests/fixtures/config-file/js/.eslintrc.parser3.js
+++ b/tests/fixtures/config-file/js/.eslintrc.parser3.js
@@ -1,7 +1,5 @@
-var defaultOptions = require("../../../../conf/default-config-options");
-
 module.exports = {
-    parser: defaultOptions.parser,
+    parser: "espree",
     rules: {
         semi: [2, "always"]
     }