Fix CSS Modules + baseUrl (#3515)

Author: drwpow

snowpack/src/build/build-import-proxy.ts

@@ -244,9 +244,10 @@ async function generateCssModuleImportProxy({
   hmr: boolean;
   config: SnowpackConfig;
 }) {
+  const reqUrl = url.replace(new RegExp(`^${config.buildOptions.baseUrl}`), '/'); // note: in build, buildOptions.baseUrl gets prepended. Remove that for looking up CSS Module code
   return `
 export let code = ${JSON.stringify(code)};
-let json = ${cssModuleJSON(url)};
+let json = ${cssModuleJSON(reqUrl)};
 export default json;
 ${
   hmr

test/snowpack/cssModules/index.test.js

@@ -162,4 +162,18 @@ describe('cssModules', () => {
     expect(result['_dist_/App.module.css']).not.toContain(`.App {`);
     expect(result['_dist_/App.module.css.json']).toBeDefined();
   });
+
+  it('Works with buildOptions.baseUrl set', async () => {
+    const result = await testFixture({
+      ...files(),
+      'snowpack.config.js': dedent`
+        module.exports = {
+          buildOptions: {
+            baseUrl: '/subdir/'
+          }
+        };
+      `,
+    });
+    expect(result['src/App.module.css.proxy.js']).toContain(`let json = {"App":"_App_`);
+  });
 });