Migration guide from 3.x to 4.x

Backward incompatible changes

Minimal required versions are:

• TypeScript (if used on the project): 4.1
• Node: v16.x

Extractor configuration changes

The big change in v4 is in extractor internals. Now it is less fragile, and doesn't depend on the host project settings.

For most projects, it should work without extra configuration as long as it is valid ES code.

extractBabelOptions is not useful anymore, please delete it from your config.

lingui.config.js

module.exports = {
-  extractBabelOptions: { [...] }
}

Hash-based message ID generation and Context feature

The previous implementation had a flaw: there is an original message in the bundle at least 2 times + 1 translation.

For the line "Hello world" it'll exist in the source code as ID in i18n call, then as a key in the message catalog, and then as a translation itself. Strings could be very long, not just a couple of words, so this may bring more kB to the bundle.

A much better option is generating a "stable" ID based on the msg + context as a hash with a fixed length.

Hash would be calculated at build time by macros. So macros instead of:

const message = t({
   context: 'My context',
   message: `Hello`
})

// ↓ ↓ ↓ ↓ ↓ ↓

import { i18n } from "@lingui/core"
const message = i18n._(/*i18n*/{
   context: 'My context',
   id: `Hello`
})

now generates:

import { i18n } from "@lingui/core"
const message = i18n._(/*i18n*/{
   id: "<hash(message + context)>",
   message: `Hello`,
})

Also, we've added a possibility to provide a context for the message. For more details, see the Providing a context for a message.

The context feature affects the message ID generation and adds the msgctxt parameter in case of the PO catalog format extraction.

Change in generated ICU messages for nested JSX Macros

We have made a small change in how Lingui generates ICU messages for nested JSX Macros. We have removed leading spaces from the texts in all cases.

The generated code from the following nested component:

<Plural
  id="message.id"
  one={
    <Trans>
      One hello
    </Trans>
  }
  other={
    <Trans>
      Other hello
    </Trans>
  }
  value={count}
/>

was changed as follows:

  <Trans
    id="message.id"
    message={
-     "{count, plural, one { One hello} other { Other hello}}"
+     "{count, plural, one {One hello} other {Other hello}}"
    }
    values={{
      count: count
    }}
  />

Flow Syntax supported in the Extractor with the flag

If your project uses Flow, you need to explicitly enable support in the extractor:

lingui.config.js

module.exports = {
  extractorParserOptions: {
    flow: true
  }
}

@lingui/cli/api/extractors/typescript was deleted

Extractor supports TypeScript out of the box. Please delete it from your configuration file.

No need to have NODE_ENV=development before lingui-extract

If your extract command looks like:

NODE_ENV=development lingui-extract

Now you can safely change it to just:

lingui-extract

Public interface of ExtractorType was changed

declare type ExtractorType = {
  match(filename: string): boolean
-   extract(filename: string, targetDir: string, options?: any): void
+   extract(
+    filename: string,
+    code: string,
+    onMessageExtracted: (msg: ExtractedMessage) => void,
+    ctx?: ExtractorCtx
+  ): Promise<void> | void
}

Read more about custom extractors on the Advanced: Custom Extractor page.

Configuration migrations for deprecated options were deleted

Migration for the following older options:

• localeDir,
• srcPathDirs,
• srcPathIgnorePatterns,
• fallbackLocale

were deleted from the source code. This should only affect users who are migrating from v2 to v4 directly.

Plural Rules now work out of the box without manual configuration

You can safely remove i18n.loadLocaleData calls because Lingui v4 uses Intl.PluralRules internally.

- import { en, cs } from "make-plural/plurals"

- i18n.loadLocaleData("en", { plurals: en })
- i18n.loadLocaleData("cs", { plurals: cs })

Don't forget to delete make-plural from your package.json.