feat(yaml): provide file id to transform function (#615)

Author: janosh

packages/yaml/README.md

@@ -90,8 +90,8 @@ A function which can optionally mutate parsed YAML. The function should return t
 
 ```js
 yaml({
-  transform(data) {
-    if (Array.isArray(data)) {
+  transform(data, filePath) {
+    if (Array.isArray(data) && filePath === './my-file.yml') {
       return data.filter(character => !character.batman);
     }
   }

packages/yaml/src/index.js

@@ -9,7 +9,7 @@ const defaults = {
 };
 const ext = /\.ya?ml$/;
 
-export default function yamll(opts = {}) {
+export default function yaml(opts = {}) {
   const options = Object.assign({}, defaults, opts);
   const { documentMode, safe } = options;
   const filter = createFilter(options.include, options.exclude);
@@ -35,7 +35,7 @@ export default function yamll(opts = {}) {
       let data = loadMethod(content);
 
       if (typeof options.transform === 'function') {
-        const result = options.transform(data);
+        const result = options.transform(data, id);
         // eslint-disable-next-line no-undefined
         if (result !== undefined) {
           data = result;

packages/yaml/test/test.js

@@ -59,8 +59,11 @@ test('resolves extensionless imports in conjunction with nodeResolve plugin', as
 });
 
 test('applies the optional transform method to parsed YAML', async (t) => {
-  const transform = (data) => {
+  const transform = (data, filePath) => {
+    // check that transformer is passed a correct file path
+    t.true(typeof filePath === 'string' && filePath.endsWith('.yaml'), filePath);
     if (Array.isArray(data)) {
+      t.true(filePath.endsWith('array.yaml'), filePath);
       return data.filter((datum) => !datum.private);
     }
     Object.keys(data).forEach((key) => {