feat(parser): Add exception for removing unused keys (#262)

* feat(parser): Add exception filter for removing unused keys

* refactor: allow the `removeUnusedKeys` function to be passed in to determine if an unused key should be removed

* chore: bump to 4.6.0

* test: enhance test case for the `removeUnusedKeys` option

---------

Co-authored-by: cheton <cheton@gmail.com>

Author: yocarbo

README.md

@@ -570,9 +570,30 @@ Set to `true` to turn on debug output.
 
 #### removeUnusedKeys
 
-Type: `Boolean` Default: `false`
+Type: `Boolean` or `Function` Default: `false`
+
+Set to `true` to remove unused translation keys from i18n resource files. By default, this is set to `false`.
+```js
+{ // Default
+    removeUnusedKeys: false,
+}
+```
 
-Set to `true` to remove unused translation keys from i18n resource files.
+If a function is provided, it will be used to decide whether an unused translation key should be removed.
+```js
+// Available since 4.6.0
+//
+// @param {string} lng The language of the unused translation key.
+// @param {string} ns The namespace of the unused translation key.
+// @param {array} key The translation key in its array form.
+// @return {boolean} Returns true if the unused translation key should be removed.
+removeUnusedKeys: function(lng, ns, key) {
+  if (ns === 'resource') {
+    return true;
+  }
+  return false;
+}
+```
 
 #### sort
 
@@ -594,7 +615,7 @@ If an `Object` is supplied, you can either specify a list of attributes and exte
 }
 ```
 
-You can set attr to `false` to disable parsing attribute as below:
+You can set `attr` to `false` to disable parsing attribute as below:
 ```js
 {
     attr: false
@@ -615,7 +636,7 @@ If an `Object` is supplied, you can either specify a list of translation functio
 }
 ```
 
-You can set func to `false` to disable parsing translation function as below:
+You can set `func` to `false` to disable parsing translation function as below:
 ```js
 {
     func: false
@@ -649,14 +670,14 @@ If an `Object` is supplied, you can specify a list of extensions, or override th
 }
 ```
 
-You can set trans to `false` to disable parsing Trans component as below:
+You can set `trans` to `false` to disable parsing Trans component as below:
 ```js
 {
     trans: false
 }
 ```
 
-The fallbackKey can either be a boolean value, or a function like so:
+The `fallbackKey` can either be a boolean value, or a function like so:
 ```js
 fallbackKey: function(ns, value) {
     // Returns a hash value as the fallback key

package.json

@@ -1,6 +1,6 @@
 {
   "name": "i18next-scanner",
-  "version": "4.5.0",
+  "version": "4.6.0",
   "description": "Scan your code, extract translation keys/values, and merge them into i18n resource files.",
   "homepage": "https://github.com/i18next/i18next-scanner",
   "author": "Cheton Wu <cheton@gmail.com>",

src/parser.js

@@ -786,7 +786,7 @@ class Parser {
     }
 
     let resStore = {};
-    if (this.options.removeUnusedKeys) {
+    if (!!this.options.removeUnusedKeys) {
       // Merge two objects `resStore` and `resScan` deeply, returning a new merged object with the elements from both `resStore` and `resScan`.
       const overwriteMerge = (destinationArray, sourceArray, options) => sourceArray;
       const resMerged = deepMerge(this.resStore, this.resScan, { arrayMerge: overwriteMerge });
@@ -798,8 +798,15 @@ class Parser {
           const unusedKeys = _.differenceWith(resStoreKeys, resScanKeys, _.isEqual);
 
           for (let i = 0; i < unusedKeys.length; ++i) {
-            _.unset(resMerged[lng][ns], unusedKeys[i]);
-            this.log(`Removed an unused translation key { ${chalk.red(JSON.stringify(unusedKeys[i]))} from ${chalk.red(JSON.stringify(this.formatResourceLoadPath(lng, ns)))}`);
+            const unusedKey = unusedKeys[i];
+            const isRemovable = (typeof this.options.removeUnusedKeys === 'function')
+              ? this.options.removeUnusedKeys(lng, ns, unusedKey)
+              : !!this.options.removeUnusedKeys;
+
+            if (isRemovable) {
+              _.unset(resMerged[lng][ns], unusedKey);
+              this.log(`Removed an unused translation key { ${chalk.red(JSON.stringify(unusedKey))} } from ${chalk.red(JSON.stringify(this.formatResourceLoadPath(lng, ns)))}`);
+            }
           }
 
           // Omit empty object

test/transform-stream.test.js

@@ -402,7 +402,12 @@ test('Keep old translations', done => {
 // https://github.com/i18next/i18next-scanner/issues/30
 test('Remove old translation keys which are already removed from code', done => {
   const options = _.merge({}, defaults, {
-    removeUnusedKeys: true,
+    removeUnusedKeys: function(lng, ns, key) {
+      if (ns === 'resource') {
+        return true;
+      }
+      return false;
+    },
     resource: {
       loadPath: 'test/fixtures/i18n/{{lng}}/{{ns}}.json',
       savePath: 'i18n/{{lng}}/{{ns}}.json'
@@ -420,7 +425,11 @@ test('Remove old translation keys which are already removed from code', done =>
       // English - locale.json
       if (file.path === 'i18n/en/locale.json') {
         const found = JSON.parse(contents);
-        const wanted = {};
+        const wanted = {
+          'language': {
+            'en-US': 'English',
+          },
+        };
         expect(found).toEqual(wanted);
       }
 
@@ -441,7 +450,11 @@ test('Remove old translation keys which are already removed from code', done =>
       // German - locale.json
       if (file.path === 'i18n/de/locale.json') {
         const found = JSON.parse(contents);
-        const wanted = {};
+        const wanted = {
+          'language': {
+            'de-DE': 'German',
+          },
+        };
         expect(found).toEqual(wanted);
       }