feat: load a JS config file (#18)

* Load a custom config: pug.config.js

* Create a config section in the README

* Do lint

* Don't swallow required module errors

* Check that used root level keys are valid

* Add comment explaining validation

README.md

@@ -12,4 +12,19 @@ Add support for [Pug].
 $ npm install hexo-renderer-pug --save
 ```
 
+## Config
+PugJS [options](https://pugjs.org/api/reference.html#options) are supported. These are the options passed into [compile()](https://pugjs.org/api/reference.html#pugcompilesource-options).
+
+Create a `pug.config.js` in your project root:
+
+```js
+module.exports = {
+  compile: {  // Passed to compile().
+    basedir: process.cwd(),
+    // ...Other options.
+  }
+  // No other methods are supported for now.
+}
+```
+
 [Pug]: http://pugjs.org/

lib/pug.js

@@ -1,11 +1,33 @@
 'use strict';
 
+const path = require('path');
 const pug = require('pug');
 
+const configPath = path.join(process.cwd(), 'pug.config');
+const defaultConfig = { compile: {} }; // avoids key errors
+
+let hasConfig = true;
+try {
+  require.resolve(configPath);
+} catch {
+  hasConfig = false;
+}
+
+const config = hasConfig ? require(configPath) : defaultConfig;
+
+// Validate non-standard keys -- e.g. 'compile'.
+const hasProp = (obj, prop) => Object.prototype.hasOwnProperty.call(obj, prop);
+const invalidKeys = Object.keys(config).filter(k => !hasProp(defaultConfig, k));
+if (invalidKeys.length > 0) {
+  throw Error(`Unsupported PUG config keys: ${invalidKeys.join(', ')}`);
+}
+
 function pugCompile(data) {
-  return pug.compile(data.text, {
-    filename: data.path
-  });
+  const opts = {
+    ...config.compile,
+    filename: data.path // always used
+  };
+  return pug.compile(data.text, opts);
 }
 
 function pugRenderer(data, locals) {