Add no-duplicate-keys-in-locale rule and change no-missing-keys rule to not report if there is one matching key in each locale (#112)

* Add no-duplicate-keys-in-locale rule and change no-missing-keys rule to not report if there is one matching key in each locale.

* fixed testcase

Author: ota-meshi

Diff for: docs/rules/README.md

@@ -16,6 +16,7 @@
 
 | Rule ID | Description |    |
 |:--------|:------------|:---|
+| [@intlify/vue-i18n/<wbr>no-duplicate-keys-in-locale](./no-duplicate-keys-in-locale.html) | disallow duplicate localization keys within the same locale |  |
 | [@intlify/vue-i18n/<wbr>no-dynamic-keys](./no-dynamic-keys.html) | disallow localization dynamic keys at localization methods |  |
 | [@intlify/vue-i18n/<wbr>no-unused-keys](./no-unused-keys.html) | disallow unused localization keys | :black_nib: |
 

Diff for: docs/rules/no-duplicate-keys-in-locale.md

@@ -0,0 +1,68 @@
+# @intlify/vue-i18n/no-duplicate-keys-in-locale
+
+> disallow duplicate localization keys within the same locale
+
+If you manage localization messages in multiple files, duplicate localization keys across multiple files can cause unexpected problems.
+
+## :book: Rule Details
+
+This rule reports duplicate localization keys within the same locale.
+
+:-1: Examples of **incorrect** code for this rule:
+
+locale messages:
+
+- `en.1.json`
+
+```json5
+// ✗ BAD
+{
+  "hello": "Hello! DIO!", // duplicate.
+  "hello": "Hello! DIO!", // duplicate.
+  "good-bye": "Good bye! DIO!"
+}
+```
+
+- `en.2.json`
+
+```json5
+// ✗ BAD
+{
+  "good-bye": "Good bye! DIO!" // This same key exists in `en.1.json`.
+}
+```
+
+:+1: Examples of **correct** code for this rule:
+
+locale messages:
+
+- `en.1.json`
+
+```json5
+// ✓ GOOD
+{
+  "hello": "Hello! DIO!",
+  "hi": "Hi! DIO!"
+}
+```
+
+- `en.2.json`
+
+```json5
+// ✓ GOOD
+{
+  "good-bye": "Good bye! DIO!" // This same key exists in `en.1.json`.
+}
+```
+
+## :gear: Options
+
+```json
+{
+  "@intlify/vue-i18n/no-duplicate-keys-in-locale": ["error", {
+    "ignoreI18nBlock": false
+  }]
+}
+```
+
+- `ignoreI18nBlock`: If `true`, do not report key duplication between `<i18n>` blocks and other files, it set to `false` as default.

Diff for: lib/rules.ts

@@ -1,4 +1,5 @@
 /** DON'T EDIT THIS FILE; was created by scripts. */
+import noDuplicateKeysInLocale from './rules/no-duplicate-keys-in-locale'
 import noDynamicKeys from './rules/no-dynamic-keys'
 import noHtmlMessages from './rules/no-html-messages'
 import noMissingKeys from './rules/no-missing-keys'
@@ -7,6 +8,7 @@ import noUnusedKeys from './rules/no-unused-keys'
 import noVHtml from './rules/no-v-html'
 
 export = {
+  'no-duplicate-keys-in-locale': noDuplicateKeysInLocale,
   'no-dynamic-keys': noDynamicKeys,
   'no-html-messages': noHtmlMessages,
   'no-missing-keys': noMissingKeys,