Update: Add resolver option to ESLint and CLIEngine

docs/developer-guide/nodejs-api.md

@@ -136,6 +136,8 @@ The `ESLint` constructor takes an `options` object. If you omit the `options` ob
   Default is `null`. The severity to report unused eslint-disable directives. If this option is a severity, it overrides the `reportUnusedDisableDirectives` setting in your configurations.
 * `options.resolvePluginsRelativeTo` (`string` | `null`)<br>
   Default is `null`. The path to a directory where plugins should be resolved from. If `null` is present, ESLint loads plugins from the location of the configuration file that contains the plugin setting. If a path is present, ESLint loads all plugins from there.
+* `options.resolver` (`ModuleResolver` | `null`)<br>
+  Default is `null`. You can use an alternate `ModuleResolver` to change how ESLint resolves plugins.
 * `options.rulePaths` (`string[]`)<br>
   Default is `[]`. An array of paths to directories to load custom rules from.
 * `options.useEslintrc` (`boolean`)<br>

lib/cli-engine/cli-engine.js

@@ -84,6 +84,7 @@ const validFixTypes = new Set(["directive", "problem", "suggestion", "layout"]);
  * @property {boolean} [reportUnusedDisableDirectives] `true` adds reports for unused eslint-disable directives
  * @property {boolean} [globInputPaths] Set to false to skip glob resolution of input file paths to lint (default: true). If false, each input file paths is assumed to be a non-glob path to an existing file.
  * @property {string} [resolvePluginsRelativeTo] The folder where plugins should be resolved from, defaulting to the CWD
+ * @property {string} [resolver] An instance of a ModuleResolver with a resolve(moduleName, relativeToPath) method.
  */
 
 /**
@@ -595,6 +596,7 @@ class CLIEngine {
             cwd: options.cwd,
             ignorePath: options.ignorePath,
             resolvePluginsRelativeTo: options.resolvePluginsRelativeTo,
+            resolve: options.resolve,
             rulePaths: options.rulePaths,
             specificConfigPath: options.configFile,
             useEslintrc: options.useEslintrc,
@@ -1008,6 +1010,10 @@ class CLIEngine {
      */
     getFormatter(format) {
 
+        // slot.options might be null, we can't destructure
+        const slot = internalSlotsMap.get(this);
+        const resolver = slot && slot.options && slot.options.resolver;
+
         // default is stylish
         const resolvedFormatName = format || "stylish";
 
@@ -1030,7 +1036,7 @@ class CLIEngine {
                 try {
                     const npmFormat = naming.normalizePackageName(normalizedFormatName, "eslint-formatter");
 
-                    formatterPath = ModuleResolver.resolve(npmFormat, path.join(cwd, "__placeholder__.js"));
+                    formatterPath = (resolver ? resolver : ModuleResolver).resolve(npmFormat, path.join(cwd, "__placeholder__.js"));
                 } catch {
                     formatterPath = path.resolve(__dirname, "formatters", normalizedFormatName);
                 }

lib/eslint/eslint.js

@@ -57,6 +57,7 @@ const { version } = require("../../package.json");
  * @property {Record<string,Plugin>} [plugins] An array of plugin implementations.
  * @property {"error" | "warn" | "off"} [reportUnusedDisableDirectives] the severity to report unused eslint-disable directives.
  * @property {string} [resolvePluginsRelativeTo] The folder where plugins should be resolved from, defaulting to the CWD.
+ * @property {string} [resolver] An instance of a ModuleResolver with a resolve(moduleName, relativeToPath) method.
  * @property {string[]} [rulePaths] An array of directories to load custom rules from.
  * @property {boolean} [useEslintrc] False disables looking for .eslintrc.* files.
  */
@@ -173,6 +174,7 @@ function processOptions({
     plugins = {},
     reportUnusedDisableDirectives = null, // ← should be null by default because if it's a string then it overrides the 'reportUnusedDisableDirectives' setting in config files. And we cannot use `overrideConfig.reportUnusedDisableDirectives` instead because we cannot configure the `error` severity with that.
     resolvePluginsRelativeTo = null, // ← should be null by default because if it's a string then it suppresses RFC47 feature.
+    resolver = null,
     rulePaths = [],
     useEslintrc = true,
     ...unknownOptions
@@ -277,6 +279,12 @@ function processOptions({
     ) {
         errors.push("'resolvePluginsRelativeTo' must be a non-empty string or null.");
     }
+    if (
+        !(resolver === null ||
+         typeof resolver === "object" && typeof resolver.resolve === "function")
+    ) {
+        errors.push("'resolver' must be an object with a 'resolver' method or null.");
+    }
     if (!isArrayOfNonEmptyString(rulePaths)) {
         errors.push("'rulePaths' must be an array of non-empty strings.");
     }
@@ -305,6 +313,7 @@ function processOptions({
         ignorePath,
         reportUnusedDisableDirectives,
         resolvePluginsRelativeTo,
+        resolver,
         rulePaths,
         useEslintrc
     };