fix: resolve default message value (#965)

resolve #964

Author: kazupon

packages/core-base/src/translate.ts

@@ -367,7 +367,7 @@ export function translate<
     isString(options.default) || isBoolean(options.default) // default by function option
       ? !isBoolean(options.default)
         ? options.default
-        : key
+        : (!messageCompiler ? () => key : key)
       : fallbackFormat // default by `fallbackFormat` option
         ? (!messageCompiler ? () => key : key)
         : ''
@@ -646,6 +646,13 @@ function compileMessageFormat<Messages, Message>(
     return msg
   }
 
+  if (messageCompiler == null) {
+    const msg = (() => format) as MessageFunctionInternal
+    msg.locale = targetLocale
+    msg.key = key
+    return msg
+  }
+
   // for vue-devtools timeline event
   let start: number | null = null
   let startTag: string | undefined
@@ -657,7 +664,7 @@ function compileMessageFormat<Messages, Message>(
     mark && mark(startTag)
   }
 
-  const msg = messageCompiler!(
+  const msg = messageCompiler(
     format as string,
     getCompileOptions(
       context,

packages/vue-i18n-core/test/issues.test.ts

@@ -470,3 +470,24 @@ test('issue #933', async () => {
 
   expect(wrapper.html()).toEqual('<div>hi! hello man! - local!</div>')
 })
+
+test('issue #964', async () => {
+  const i18n = createI18n({
+    legacy: false,
+    locale: 'ja',
+    fallbackLocale: 'en',
+    messages: {
+      en: {
+        hello: 'hello man!'
+      }
+    }
+  })
+  const { t } = i18n.global
+
+  // set no compiler
+  registerMessageCompiler(null as any) // eslint-disable-line @typescript-eslint/no-explicit-any
+
+  const defaultMsg = t('foo')
+  expect(defaultMsg).toEqual('foo')
+  expect(t('bar', defaultMsg)).toEqual('foo')
+})