Add support for preprocessing with node-sass

package.json

@@ -10,6 +10,7 @@
     "babel-plugin-syntax-jsx": "^6.18.0",
     "babel-types": "^6.26.0",
     "generic-names": "^1.0.3",
+    "node-sass": "^4.9.0",
     "postcss": "^6.0.22",
     "postcss-modules": "^1.1.0",
     "postcss-modules-extract-imports": "^1.1.0",

src/requireCssModule.js

@@ -7,6 +7,7 @@ import {
 import {
   readFileSync
 } from 'fs';
+import sass from 'node-sass';
 import postcss from 'postcss';
 import genericNames from 'generic-names';
 import ExtractImports from 'postcss-modules-extract-imports';
@@ -21,13 +22,19 @@ import type {
 
 type FiletypeOptionsType = {|
   +syntax: string,
-  +plugins?: $ReadOnlyArray<string | $ReadOnlyArray<[string, mixed]>>
+  +plugins?: $ReadOnlyArray<string | $ReadOnlyArray<[string, mixed]>>,
+  +importer?: string | $ReadOnlyArray<string>
 |};
 
 type FiletypesConfigurationType = {
   [key: string]: FiletypeOptionsType
 };
 
+type SassOptionsType = {|
+  file: string,
+  importer?: Array<[mixed]>
+|};
+
 const getFiletypeOptions = (cssSourceFilePath: string, filetypes: FiletypesConfigurationType): ?FiletypeOptionsType => {
   const extension = cssSourceFilePath.substr(cssSourceFilePath.lastIndexOf('.'));
   const filetype = filetypes ? filetypes[extension] : null;
@@ -70,12 +77,27 @@ const getTokens = (runner, cssSourceFilePath: string, filetypeOptions: ?Filetype
     from: cssSourceFilePath
   };
 
+  let fileContents = readFileSync(cssSourceFilePath, 'utf-8');
+
   if (filetypeOptions) {
-    options.syntax = getSyntax(filetypeOptions);
+    if (filetypeOptions.syntax === 'node-sass') {
+      const sassOptions: SassOptionsType = {file: cssSourceFilePath};
+
+      if (filetypeOptions.importer) {
+        sassOptions.importer = [].concat(filetypeOptions.importer).map((importerName) => {
+          // eslint-disable-next-line import/no-dynamic-require, global-require
+          return require(importerName);
+        });
+      }
+
+      fileContents = sass.renderSync(sassOptions).css.toString();
+    } else {
+      options.syntax = getSyntax(filetypeOptions);
+    }
   }
 
   const lazyResult = runner
-    .process(readFileSync(cssSourceFilePath, 'utf-8'), options);
+    .process(fileContents, options);
 
   lazyResult
     .warnings()

src/schemas/optionsSchema.json

@@ -28,6 +28,16 @@
             },
             "syntax": {
               "type": "string"
+            },
+            "importer": {
+              "oneOf": [
+                {
+                  "type": "string"
+                },
+                {
+                  "type": "array"
+                }
+              ]
             }
           },
           "type": "object"