Cannot extract message keys build by string interpolation

[cbenz]

When running svelte-i18n extract as documented here on a file that formats a message with $_ using a message key build by string interpolation or concatenation, the CLI tool crashes with an exception.

There is such a message key in the Sapper template for svelte-i18n: $_('languages.' + item.replace('-', '_')) (source).

How to reproduce:

$ git clone https://github.com/kaisermann/sapper-template-i18n.git
$ npm install
$ ./node_modules/.bin/svelte-i18n extract "src/components/Nav.svelte"
(node:1180263) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'split' of undefined
    at /home/cbenz/Dev/vendor/sapper-template-i18n/node_modules/svelte-i18n/dist/cli.js:17:2801
    at Array.forEach (<anonymous>)
    at h (/home/cbenz/Dev/vendor/sapper-template-i18n/node_modules/svelte-i18n/dist/cli.js:17:2644)
    at Command.<anonymous> (/home/cbenz/Dev/vendor/sapper-template-i18n/node_modules/svelte-i18n/dist/cli.js:17:4131)
(Use `node --trace-warnings ...` to show where the warning was created)
(node:1180263) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 2)
(node:1180263) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

I've tried with some other patterns that also fail with the same exception:

$('key.' + value)
$(`key.${value}`)

Expected behavior: the message extractor could display a warning, and skip this message key. I understand that it can't guess all the possible values of the string interpolation.

I'm using:

• node v14.2.0 (Arch Linux)
• svelte-i18n 3.0.4 (latest version at the time I write the issue)

[kaisermann]

Hey, @cbenz 👋 Fixed in 3.2.3 🎉 However, I didn't add any kind of warning/log for now.

[cbenz]

Wow, that awesome, thanks!