Add support for shareable/extendable configuration via "extends" and helper functions (fixes #33).

lib/markdownlint.js

@@ -1,6 +1,7 @@
 "use strict";
 
 var fs = require("fs");
+var path = require("path");
 var md = require("markdown-it")({ "html": true });
 var rules = require("./rules");
 var shared = require("./shared");
@@ -329,7 +330,7 @@ function markdownlintSynchronousCallback() {
 }
 
 /**
- * Lint specified Markdown files according to configurable rules.
+ * Lint specified Markdown files.
  *
  * @param {Object} options Configuration options.
  * @param {Function} callback Callback (err, result) function.
@@ -387,7 +388,7 @@ function markdownlint(options, callback) {
 }
 
 /**
- * Lint specified Markdown files according to configurable rules.
+ * Lint specified Markdown files synchronously.
  *
  * @param {Object} options Configuration options.
  * @returns {Object} Result object.
@@ -396,6 +397,63 @@ function markdownlintSync(options) {
   return markdownlint(options, markdownlintSynchronousCallback);
 }
 
+/**
+ * Read specified configuration file.
+ *
+ * @param {String} file Configuration file name/path.
+ * @param {Function} callback Callback (err, result) function.
+ * @returns {void}
+ */
+function readConfig(file, callback) {
+  // Read file
+  fs.readFile(file, shared.utf8Encoding, function handleFile(err, content) {
+    if (err) {
+      return callback(err);
+    }
+    // Parse file
+    var config = null;
+    try {
+      config = JSON.parse(content);
+    } catch (ex) {
+      return callback(ex);
+    }
+    if (config.extends) {
+      // Extend configuration
+      var extendsFile = path.resolve(path.dirname(file), config.extends);
+      readConfig(extendsFile, function handleConfig(errr, extendsConfig) {
+        if (errr) {
+          return callback(errr);
+        }
+        delete config.extends;
+        callback(null, shared.assign(extendsConfig, config));
+      });
+    } else {
+      callback(null, config);
+    }
+  });
+}
+
+/**
+ * Read specified configuration file synchronously.
+ *
+ * @param {String} file Configuration file name/path.
+ * @returns {Object} Configuration object.
+ */
+function readConfigSync(file) {
+  // Parse file
+  var config = JSON.parse(fs.readFileSync(file, shared.utf8Encoding));
+  if (config.extends) {
+    // Extend configuration
+    config = shared.assign(
+      readConfigSync(path.resolve(path.dirname(file), config.extends)),
+      config);
+    delete config.extends;
+  }
+  return config;
+}
+
 // Export a/synchronous APIs
 module.exports = markdownlint;
 module.exports.sync = markdownlintSync;
+module.exports.readConfig = readConfig;
+module.exports.readConfigSync = readConfigSync;