Allow custom file system implementation to be passed when linting or reading configuration.

lib/markdownlint.js

@@ -2,7 +2,6 @@
 
 "use strict";
 
-const fs = require("fs");
 const path = require("path");
 const { promisify } = require("util");
 const markdownIt = require("markdown-it");
@@ -685,6 +684,7 @@ function lintContent(
  * @param {boolean} handleRuleFailures Whether to handle exceptions in rules.
  * @param {boolean} noInlineConfig Whether to allow inline configuration.
  * @param {number} resultVersion Version of the LintResults object to return.
+ * @param {Object} fs File system implementation.
  * @param {boolean} synchronous Whether to execute synchronously.
  * @param {Function} callback Callback (err, result) function.
  * @returns {void}
@@ -698,6 +698,7 @@ function lintFile(
   handleRuleFailures,
   noInlineConfig,
   resultVersion,
+  fs,
   synchronous,
   callback) {
   // eslint-disable-next-line jsdoc/require-jsdoc
@@ -710,7 +711,6 @@ function lintFile(
   }
   // Make a/synchronous call to read file
   if (synchronous) {
-    // @ts-ignore
     lintContentWrapper(null, fs.readFileSync(file, "utf8"));
   } else {
     fs.readFile(file, "utf8", lintContentWrapper);
@@ -756,6 +756,7 @@ function lintInput(options, synchronous, callback) {
     // @ts-ignore
     md.use(...plugin);
   });
+  const fs = options.fs || require("fs");
   const results = newResults(ruleList);
   let done = false;
   // Linting of strings is always synchronous
@@ -795,6 +796,7 @@ function lintInput(options, synchronous, callback) {
         handleRuleFailures,
         noInlineConfig,
         resultVersion,
+        fs,
         synchronous,
         syncCallback
       );
@@ -819,6 +821,7 @@ function lintInput(options, synchronous, callback) {
         handleRuleFailures,
         noInlineConfig,
         resultVersion,
+        fs,
         synchronous,
         (err, result) => {
           concurrency--;
@@ -929,17 +932,17 @@ function parseConfiguration(name, content, parsers) {
  *
  * @param {string} configFile Configuration file name.
  * @param {string} referenceId Referenced identifier to resolve.
+ * @param {Object} fs File system implementation.
  * @returns {string} Resolved path to file.
  */
-function resolveConfigExtends(configFile, referenceId) {
+function resolveConfigExtends(configFile, referenceId, fs) {
   const configFileDirname = path.dirname(configFile);
   const resolvedExtendsFile = path.resolve(configFileDirname, referenceId);
   try {
-    if (fs.statSync(resolvedExtendsFile).isFile()) {
-      return resolvedExtendsFile;
-    }
+    fs.accessSync(resolvedExtendsFile);
+    return resolvedExtendsFile;
   } catch {
-    // If not a file or fs.statSync throws, try require.resolve
+    // Not a file, try require.resolve
   }
   try {
     return dynamicRequire.resolve(
@@ -947,7 +950,7 @@ function resolveConfigExtends(configFile, referenceId) {
       { "paths": [ configFileDirname ] }
     );
   } catch {
-    // If require.resolve throws, return resolvedExtendsFile
+    // Unable to resolve, return resolvedExtendsFile
   }
   return resolvedExtendsFile;
 }
@@ -958,14 +961,23 @@ function resolveConfigExtends(configFile, referenceId) {
  * @param {string} file Configuration file name.
  * @param {ConfigurationParser[] | ReadConfigCallback} parsers Parsing
  * function(s).
+ * @param {Object} [fs] File system implementation.
  * @param {ReadConfigCallback} [callback] Callback (err, result) function.
  * @returns {void}
  */
-function readConfig(file, parsers, callback) {
+function readConfig(file, parsers, fs, callback) {
   if (!callback) {
-    // @ts-ignore
-    callback = parsers;
-    parsers = null;
+    if (fs) {
+      callback = fs;
+      fs = null;
+    } else {
+      // @ts-ignore
+      callback = parsers;
+      parsers = null;
+    }
+  }
+  if (!fs) {
+    fs = require("fs");
   }
   // Read file
   fs.readFile(file, "utf8", (err, content) => {
@@ -982,8 +994,8 @@ function readConfig(file, parsers, callback) {
     const configExtends = config.extends;
     if (configExtends) {
       delete config.extends;
-      const resolvedExtends = resolveConfigExtends(file, configExtends);
-      return readConfig(resolvedExtends, parsers, (errr, extendsConfig) => {
+      const resolvedExtends = resolveConfigExtends(file, configExtends, fs);
+      return readConfig(resolvedExtends, parsers, fs, (errr, extendsConfig) => {
         if (errr) {
           return callback(errr);
         }
@@ -1004,11 +1016,12 @@ const readConfigPromisify = promisify && promisify(readConfig);
  *
  * @param {string} file Configuration file name.
  * @param {ConfigurationParser[]} [parsers] Parsing function(s).
+ * @param {Object} [fs] File system implementation.
  * @returns {Promise<Configuration>} Configuration object.
  */
-function readConfigPromise(file, parsers) {
+function readConfigPromise(file, parsers, fs) {
   // @ts-ignore
-  return readConfigPromisify(file, parsers);
+  return readConfigPromisify(file, parsers, fs);
 }
 
 /**
@@ -1016,11 +1029,14 @@ function readConfigPromise(file, parsers) {
  *
  * @param {string} file Configuration file name.
  * @param {ConfigurationParser[]} [parsers] Parsing function(s).
+ * @param {Object} [fs] File system implementation.
  * @returns {Configuration} Configuration object.
  */
-function readConfigSync(file, parsers) {
+function readConfigSync(file, parsers, fs) {
+  if (!fs) {
+    fs = require("fs");
+  }
   // Read file
-  // @ts-ignore
   const content = fs.readFileSync(file, "utf8");
   // Try to parse file
   const { config, message } = parseConfiguration(file, content, parsers);
@@ -1031,9 +1047,9 @@ function readConfigSync(file, parsers) {
   const configExtends = config.extends;
   if (configExtends) {
     delete config.extends;
-    const resolvedExtends = resolveConfigExtends(file, configExtends);
+    const resolvedExtends = resolveConfigExtends(file, configExtends, fs);
     return {
-      ...readConfigSync(resolvedExtends, parsers),
+      ...readConfigSync(resolvedExtends, parsers, fs),
       ...config
     };
   }
@@ -1156,6 +1172,7 @@ module.exports = markdownlint;
  * @property {boolean} [noInlineConfig] True to ignore HTML directives.
  * @property {number} [resultVersion] Results object version.
  * @property {Plugin[]} [markdownItPlugins] Additional plugins.
+ * @property {Object} [fs] File system implementation.
  */
 
 /**