regeneratorRuntime required with @fluent/bundle even when not using the compat build #497

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1. stasm commented on Jun 17, 2020

   

   stasm

   on Jun 17, 2020

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   Thank you for a comprehensive issue report!

   In #472 I removed the compat builds altogether and in #483 I removed the mention of regeneratorRuntime from the README. I was planning to continue the build system cleanups in #480 but I hit a roadblock. I needlessly put off releasing new versions of all @fluent packages until I can figure how to fix it. I'm sorry about that, I'll work on releasing new versions next week.

   The main motivation for removing the compat builds in #472 was that today's build tools are capable of transpiling dependencies which means we should be able to provide a single version of a @fluent package written in fairly modern JS, and the build tool will transpile it if needed.

   In your example, I assume that browserify is transpiling all code, including the @fluent/bundle dependency. So even if you're not using the compat build, you end up with a transpiled version of @fluent/bundle anyways; hence the need for the regeneratorRuntime. Am I understanding this right?
2. elisehein commented on Jun 17, 2020

   

   elisehein

   on Jun 17, 2020

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   In your example, I assume that browserify is transpiling all code, including the @fluent/bundle dependency. So even if you're not using the compat build, you end up with a transpiled version of @fluent/bundle anyways; hence the need for the regeneratorRuntime. Am I understanding this right?

   I'm indeed using browserify, but as far as I'm aware, the transforms (babelify with @babel/preset-env) do not automatically apply to files in node_modules, so the expectation is that any packages imported from node modules are already transpiled, and are just included in the bundle as-is. So that still leaves me a bit confused about regeneratorRuntime popping up in the transpiled code...
3. Pike commented on Jun 17, 2020

   

   Pike

   on Jun 17, 2020

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   About that piece of doc, IIRC that was supposed to mean:

   If you're not using the compat builds, you need a fancy new browser, and anything just slightly old will break in all kinds of ways.
   If you want older browsers, the compat builds get you far, but we didn't include the regenerators, as you might need them elsewhere, and then your transpiled js would get unnecessarily large.

   So you need generators either way, but the non-compat builds break on a lot more than just that.
4. elisehein commented on Jun 17, 2020

   

   elisehein

   on Jun 17, 2020

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   @Pike Thanks, that makes sense!
5. stasm commented on Jun 17, 2020

   

   stasm

   on Jun 17, 2020

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   so the expectation is that any packages imported from node modules are already transpiled, and are just included in the bundle as-is. So that still leaves me a bit confused about regeneratorRuntime popping up in the transpiled code...

   Could it be that browserify (or babelify?) uses the regeneratorRuntime to transpile the *generateBundle(locale) generator function in your index.js?

   In fact, @fluent/bundle doesn't even use yield nor async functions; even transpiled, it wouldn't require the runtime to be present for legacy browsers. OTOH the runtime would be needed for transpiled versions of packages like @fluent/dom and @fluent/react.
6. elisehein commented on Jun 17, 2020

   

   elisehein

   on Jun 17, 2020

   Last edited by elisehein

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   @stasm Indeed, thanks, that looks like it's the crux of it!

   To test, when I replace *generateBundle with a vanilla JS function that only pretends to return a generator, I no longer need to import regeneratorRuntime:

   function generateBundle(locale) {
     const bundle = new FluentBundle(locale);
     bundle.addResource(bundle.addResource(new FluentResource("hello = Hola!"));
     let result = {};
     result[Symbol.iterator] = () => {
       return {
         next: () => {
           return {
             done: true,
             value: bundle
           };
         }
       };
     };
   
     return result;
   }
   

   I'll close this issue now, thanks all for helping me investigate.

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7. elisehein

   closed this as completedon Jun 17, 2020