⭐ new(rule): add no-unused-key rule

Author: kazupon

README.md

@@ -18,7 +18,7 @@ Details changes for each release are documented in the [CHANGELOG.md](https://gi
 ## :white_check_mark: TODO
 - [x] no-missing-key
 - [ ] no-dynamic-key
-- [ ] no-unused-key
+- [x] no-unused-key
 - [ ] no-raw-text
 - [ ] valid-message-syntax
 - [ ] keys-order

docs/.vuepress/config.js

@@ -1,3 +1,7 @@
+/**
+ * @fileoverview VuePress configration
+ * @author kazuya kawaguchi (a.k.a. kazupon)
+ */
 'use strict'
 
 const { withCategories } = require('../../scripts/lib/rules')

docs/rules/README.md

@@ -9,3 +9,9 @@
 |:--------|:------------|:---|
 | [vue-i18n/<wbr>no-missing-key](./no-missing-key.html) | disallow missing locale message key at localization methods | :star: |
 
+## Best Practices
+
+| Rule ID | Description |    |
+|:--------|:------------|:---|
+| [vue-i18n/<wbr>no-unused-key](./no-unused-key.html) | disallow unused localization keys |  |
+

docs/rules/no-unused-key.md

@@ -0,0 +1,87 @@
+# vue-i18n/no-unused-key
+
+> disallow unused localization keys
+
+Localization keys that not used anywhere in the code are most likely an error due to incomplete refactoring. Such localization keys take up code size and can lead to confusion by readers.
+
+## :book: Rule Details
+
+This rule is aimed at eliminating unused localization keys.
+
+:-1: Examples of **incorrect** code for this rule:
+
+locale messages:
+```js
+// ✗ BAD
+{
+  "hello": "Hello! DIO!",
+  "hi": "Hi! DIO!" // not used in application
+}
+```
+
+In localization codes of application:
+
+```vue
+<template>
+  <div class="app">
+    <p>{{ $t('hello') }}</p>
+  </div>
+</template>
+```
+
+```js
+const i18n = new VueI18n({
+  locale: 'en',
+  messages: {
+    en: require('./locales/en.json')
+  }
+})
+
+i18n.t('hello')
+```
+
+:+1: Examples of **correct** code for this rule:
+
+locale messages:
+// ✓ GOOD
+```js
+{
+  "hello": "Hello! DIO!",
+  "hi": "Hi! DIO!"
+}
+```
+
+In localization codes of application:
+
+```vue
+<template>
+  <div class="app">
+    <p>{{ $t('hello') }}</p>
+  </div>
+</template>
+```
+
+```js
+const i18n = new VueI18n({
+  locale: 'en',
+  messages: {
+    en: require('./locales/en.json')
+  }
+})
+
+i18n.t('hi')
+```
+
+## Options
+
+You can specify allowed directive-comments.
+
+```json
+{
+  "vue-i18n/no-unused-key": ["error", {
+    "extensions": [".js", ".vue"]
+  }]
+}
+```
+
+- `extenstions`: an array to allow specified lintable target file extention. If you don't set any options, it set to `.js` and` .vue` as default.

lib/index.js

@@ -7,5 +7,5 @@
 module.exports = {
   configs: require('./configs'),
   rules: require('./rules'),
-  processors: {}
+  processors: require('./processors')
 }

lib/processors.js

@@ -0,0 +1,6 @@
+/** DON'T EDIT THIS FILE; was created by scripts. */
+'use strict'
+
+module.exports = {
+  '.json': require('./processors/json')
+}

lib/processors/.gitkeep

@@ -0,0 +1,26 @@
+/**
+ * @fileoverview JSON processor
+ * @author kazuya kawaguchi (a.k.a. kazupon)
+ */
+'use strict'
+
+const localeMessageFiles = {}
+
+module.exports = {
+  preprocess (text, filename) {
+    localeMessageFiles[filename] = text
+    // JSON into a JavaScript comment
+    const textBuf = Buffer.from(text.trim())
+    const filenameBuf = Buffer.from(filename)
+    return [`/*${textBuf.toString('base64')}*//*${filenameBuf.toString('base64')}*/\n`]
+  },
+
+  postprocess ([errors], filename) {
+    delete localeMessageFiles[filename]
+    return [...errors.filter(
+      error => !error.ruleId || error.ruleId === 'vue-i18n/no-unused-key'
+    )]
+  },
+
+  supportsAutofix: true
+}

lib/processors/json.js

@@ -2,5 +2,6 @@
 'use strict'
 
 module.exports = {
-  'no-missing-key': require('./rules/no-missing-key')
+  'no-missing-key': require('./rules/no-missing-key'),
+  'no-unused-key': require('./rules/no-unused-key')
 }

lib/rules.js

@@ -0,0 +1,141 @@
+/**
+ * @author kazuya kawaguchi (a.k.a. kazupon)
+ */
+'use strict'
+
+const { extname } = require('path')
+const jsonAstParse = require('json-to-ast')
+const jsonDiffPatch = require('jsondiffpatch').create({})
+const flatten = require('flat')
+const collectKeys = require('../utils/collect-keys')
+const { loadLocaleMessages } = require('../utils/index')
+const debug = require('debug')('eslint-plugin-vue-i18n:no-unused-key')
+
+let usedLocaleMessageKeys = null // used locale message keys
+let localeMessages = null // used locale messages
+
+function findExistLocaleMessage (fullpath, localeMessages) {
+  return localeMessages.find(message => message.fullpath === fullpath)
+}
+
+function getUnusedKeys (diffLocaleMessage) {
+  const unusedKeys = []
+  Object.keys(diffLocaleMessage).forEach(key => {
+    const value = diffLocaleMessage[key]
+    if (value && Array.isArray(value) && value.length === 1) {
+      unusedKeys.push(key)
+    }
+  })
+  return unusedKeys
+}
+
+function traverseJsonAstWithUnusedKeys (unusedKeys, ast, fn) {
+  unusedKeys.forEach(key => {
+    const fullpath = String(key)
+    const paths = key.split('.')
+    traverseNode(fullpath, paths, ast, fn)
+  })
+}
+
+function traverseNode (fullpath, paths, ast, fn) {
+  const path = paths.shift()
+  if (ast.type === 'Object' && ast.children.length > 0) {
+    ast.children.forEach(child => {
+      if (child.type === 'Property') {
+        const key = child.key
+        if (key.type === 'Identifier' && key.value === path) {
+          const value = child.value
+          if (value.type === 'Object') {
+            return traverseNode(fullpath, paths, value, fn)
+          } else {
+            return fn(fullpath, key)
+          }
+        }
+      }
+    })
+  }
+}
+
+function create (context) {
+  const filename = context.getFilename()
+  if (extname(filename) !== '.json') {
+    debug(`ignore ${filename} in no-unused-key`)
+    return {}
+  }
+
+  const { settings } = context
+  if (!settings['vue-i18n'] || !settings['vue-i18n'].localeDir) {
+    // TODO: should be error
+    return {}
+  }
+  localeMessages = localeMessages || loadLocaleMessages(settings['vue-i18n'].localeDir)
+
+  const targetLocaleMessage = findExistLocaleMessage(filename, localeMessages)
+  if (!targetLocaleMessage) {
+    debug(`ignore ${filename} in no-unused-key`)
+    return {}
+  }
+
+  const { extensions } = (context.options && context.options[0]) || { extensions: ['.js', '.vue'] }
+  const src = [process.cwd()] || ['.']
+
+  if (!usedLocaleMessageKeys) {
+    usedLocaleMessageKeys = collectKeys(src, extensions)
+  }
+
+  return {
+    Program (node) {
+      const [stringNode, filenameNode] = node.comments
+      const jsonString = Buffer.from(stringNode.value, 'base64').toString()
+      const jsonFilename = Buffer.from(filenameNode.value, 'base64').toString()
+      const jsonValue = JSON.parse(jsonString)
+      try {
+        const diffValue = jsonDiffPatch.diff(
+          flatten(usedLocaleMessageKeys, { safe: true }),
+          flatten(jsonValue, { safe: true })
+        )
+        const diffLocaleMessage = flatten(diffValue, { safe: true })
+        const unusedKeys = getUnusedKeys(diffLocaleMessage)
+
+        const jsonAstSettings = { loc: true, source: jsonFilename }
+        const ast = jsonAstParse(jsonString, jsonAstSettings)
+        traverseJsonAstWithUnusedKeys(unusedKeys, ast, (fullpath, node) => {
+          const { line, column } = node.loc.start
+          context.report({
+            message: `unused '${fullpath}' key in '${targetLocaleMessage.path}'`,
+            loc: { line, column }
+          })
+        })
+      } catch ({ message, line, column }) {
+        context.report({
+          message,
+          loc: { line, column }
+        })
+      }
+    }
+  }
+}
+
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow unused localization keys',
+      category: 'Best Practices',
+      recommended: false
+    },
+    fixable: false,
+    schema: [{
+      type: 'object',
+      properties: {
+        extensions: {
+          type: 'array',
+          items: { type: 'string' },
+          default: ['.js', '.vue']
+        }
+      },
+      additionalProperties: false
+    }]
+  },
+  create
+}