Add support for JS configuration via --config (fixes #85).

Author: DavidAnson

README.md

@@ -24,7 +24,7 @@ markdownlint --help
     -f, --fix                                   fix basic errors (does not work with STDIN)
     -s, --stdin                                 read from STDIN (does not work with files)
     -o, --output [outputFile]                   write issues to file (no console)
-    -c, --config [configFile]                   configuration file (JSON, JSONC, or YAML)
+    -c, --config [configFile]                   configuration file (JSON, JSONC, JS, or YAML)
     -i, --ignore [file|directory|glob]          file(s) to ignore/exclude
     -p, --ignore-path [file]                    path to file with ignore pattern(s)
     -r, --rules  [file|directory|glob|package]  custom rule files
@@ -83,10 +83,14 @@ The example of configuration file:
 
 See [test configuration file][test-config] or [style folder][style-folder] for more examples.
 
-CLI argument `--config` is not mandatory.
-If it is not provided, `markdownlint-cli` looks for file `.markdownlint.json`/`.markdownlint.yaml`/`.markdownlint.yml` in current folder, or for file `.markdownlintrc` in current or all upper folders.
-The algorithm is described in details on [rc package page][rc-standards].
-If `--config` argument is provided, the file must be valid JSON, JSONC, or YAML.
+The CLI argument `--config` is not required.
+If it is not provided, `markdownlint-cli` looks for the file `.markdownlint.json`/`.markdownlint.yaml`/`.markdownlint.yml` in current folder, or for the file `.markdownlintrc` in the current or all parent folders.
+The algorithm is described in detail on the [`rc` package page][rc-standards].
+If the `--config` argument is provided, the file must be valid JSON, JSONC, JS, or YAML.
+JS configuration files contain JavaScript code, must have the `.js` extension, and must export (via `module.exports = ...`) a configuration object of the form shown above.
+A JS configuration file may internally `require` one or more npm packages as a way of reusing configuration across projects.
+
+> JS configuration files must be provided via the `--config` argument; they are not automatically loaded because running untrusted code is a security concern.
 
 ## Exit codes
 

markdownlint.js

@@ -12,6 +12,7 @@ const markdownlint = require('markdownlint');
 const rc = require('rc');
 const glob = require('glob');
 const minimatch = require('minimatch');
+const minimist = require('minimist');
 const pkg = require('./package');
 
 function jsoncParse(text) {
@@ -29,10 +30,19 @@ const projectConfigFiles = [
 ];
 const configFileParsers = [jsoncParse, jsYamlSafeLoad];
 const fsOptions = {encoding: 'utf8'};
+const processCwd = process.cwd();
 
 function readConfiguration(args) {
-  let config = rc('markdownlint', {});
   const userConfigFile = args.config;
+  const jsConfigFile = /\.js$/i.test(userConfigFile);
+  const rcArgv = minimist(process.argv.slice(2));
+  if (jsConfigFile) {
+    // Prevent rc package from parsing .js config file as INI
+    delete rcArgv.config;
+  }
+
+  // Load from well-known config files
+  let config = rc('markdownlint', {}, rcArgv);
   for (const projectConfigFile of projectConfigFiles) {
     try {
       fs.accessSync(projectConfigFile, fs.R_OK);
@@ -43,17 +53,21 @@ function readConfiguration(args) {
       // Ignore failure
     }
   }
+
   // Normally parsing this file is not needed,
   // because it is already parsed by rc package.
   // However I have to do it to overwrite configuration
   // from .markdownlint.{json,yaml,yml}.
-
   if (userConfigFile) {
     try {
-      const userConfig = markdownlint.readConfigSync(userConfigFile, configFileParsers);
+      const userConfig = jsConfigFile ?
+        // Evaluate .js configuration file as code
+        require(path.resolve(processCwd, userConfigFile)) :
+        // Load JSON/YAML configuration as data
+        markdownlint.readConfigSync(userConfigFile, configFileParsers);
       config = require('deep-extend')(config, userConfig);
     } catch (error) {
-      console.warn('Cannot read or parse config file ' + args.config + ': ' + error.message);
+      console.warn('Cannot read or parse config file ' + userConfigFile + ': ' + error.message);
     }
   }
 
@@ -78,7 +92,7 @@ function prepareFileList(files, fileExtensions, previousResults) {
         // Directory (file falls through to below)
         if (previousResults) {
           const matcher = new minimatch.Minimatch(
-            path.resolve(process.cwd(), path.join(file, '**', extensionGlobPart)), globOptions);
+            path.resolve(processCwd, path.join(file, '**', extensionGlobPart)), globOptions);
           return previousResults.filter(function (fileInfo) {
             return matcher.match(fileInfo.absolute);
           }).map(function (fileInfo) {
@@ -91,7 +105,7 @@ function prepareFileList(files, fileExtensions, previousResults) {
     } catch (_) {
       // Not a directory, not a file, may be a glob
       if (previousResults) {
-        const matcher = new minimatch.Minimatch(path.resolve(process.cwd(), file), globOptions);
+        const matcher = new minimatch.Minimatch(path.resolve(processCwd, file), globOptions);
         return previousResults.filter(function (fileInfo) {
           return matcher.match(fileInfo.absolute);
         }).map(function (fileInfo) {
@@ -108,7 +122,7 @@ function prepareFileList(files, fileExtensions, previousResults) {
   return flatten(files).map(function (file) {
     return {
       original: file,
-      relative: path.relative(process.cwd(), file),
+      relative: path.relative(processCwd, file),
       absolute: path.resolve(file)
     };
   });
@@ -171,7 +185,7 @@ program
   .option('-f, --fix', 'fix basic errors (does not work with STDIN)')
   .option('-s, --stdin', 'read from STDIN (does not work with files)')
   .option('-o, --output [outputFile]', 'write issues to file (no console)')
-  .option('-c, --config [configFile]', 'configuration file (JSON, JSONC, or YAML)')
+  .option('-c, --config [configFile]', 'configuration file (JSON, JSONC, JS, or YAML)')
   .option('-i, --ignore [file|directory|glob]', 'file(s) to ignore/exclude', concatArray, [])
   .option('-p, --ignore-path [file]', 'path to file with ignore pattern(s)')
   .option('-r, --rules  [file|directory|glob|package]', 'custom rule files', concatArray, []);
@@ -183,7 +197,7 @@ function tryResolvePath(filepath) {
     if (path.basename(filepath) === filepath && path.extname(filepath) === '') {
       // Looks like a package name, resolve it relative to cwd
       // Get list of directories, where requested module can be.
-      let paths = Module._nodeModulePaths(process.cwd());
+      let paths = Module._nodeModulePaths(processCwd);
       paths = paths.concat(Module.globalPaths);
       if (require.resolve.paths) {
         // Node >= 8.9.0
@@ -194,7 +208,7 @@ function tryResolvePath(filepath) {
     }
 
     // Maybe it is a path to package installed locally
-    return require.resolve(path.join(process.cwd(), filepath));
+    return require.resolve(path.join(processCwd, filepath));
   } catch (_) {
     return filepath;
   }

package.json

@@ -49,6 +49,7 @@
     "markdownlint": "~0.20.2",
     "markdownlint-rule-helpers": "~0.9.0",
     "minimatch": "~3.0.4",
+    "minimist": "~1.2.5",
     "rc": "~1.2.7"
   },
   "devDependencies": {
@@ -72,7 +73,8 @@
   "ava": {
     "files": [
       "test/**/*.js",
-      "!test/custom-rules/**/*.js"
+      "!test/custom-rules/**/*.js",
+      "!test/md043-config.js"
     ],
     "failFast": true
   }

test/md043-config.js

@@ -0,0 +1,14 @@
+'use strict';
+
+// Export config object directly (as below)
+// -OR-
+// via require('some-npm-module-that-exports-config')
+module.exports = {
+  MD043: {
+    headers: [
+      '# First',
+      '## Second',
+      '### Third'
+    ]
+  }
+};

test/test.js

@@ -365,6 +365,14 @@ test('configuration file can be YAML', async t => {
   t.is(result.stderr, '');
 });
 
+test('configuration file can be JavaScript', async t => {
+  const result = await execa('../markdownlint.js',
+    ['--config', 'md043-config.js', 'md043-config.md'],
+    {stripFinalNewline: false});
+  t.is(result.stdout, '');
+  t.is(result.stderr, '');
+});
+
 function getCwdConfigFileTest(extension) {
   return async t => {
     try {