[Discussion] Better Flow setup

[radex]

In #19 I fixed support for using Flow in apps importing Watermelon.

But there's a couple of problems:

1. We can't just export the source code, because we have to rewrite imports first (see [Discussion] Absolute vs relative paths #20), which complicates the build process
2. Babel screws up the $FlowFixMe comments in the output files, so we have to re-check Flow in an app importing Watermelon
3. We have to build a separate package for Flow. Use https://babeljs.io/docs/en/babel-plugin-transform-flow-comments maybe to use the same exported code as apps use?
4. Flow in an app will flow-check the entire Watermelon, which takes more time and is likely to break if there's a mismatch of Flow version used in Watermelon and the app. We could manually write flow-typed, but that's extra maintenance burden.

Can we generate flow-typed automatically from source?.

Or, alternatively: Can apps configure Flow to only import types, but don't actually output errors for Flow issues inside Watermelon?

[jamesisaac]

Or, alternatively: Can apps configure Flow to only import types, but don't actually output errors for Flow issues inside Watermelon?

The [declarations] config section in Flow 0.76 should allow this: facebook/flow#4916 (PR talks about [silence] but it was renamed to [declarations] just before release).

[radex]

Oh, that's so cool! Thanks @jamesisaac. I will check it out on Friday if it actually works :)

[jamesisaac]

You're welcome! Cool library (just saw it on HN), looking forward to giving it a try. Great to see the focus on Flow / type safety.

[wcandillon]

My understanding is that [declarations] doesn't work at the moment. Am I correct? I'm also confused on how people are able to use latest versions of Flow successfully with React/React Native. The documentation doesn't seem to indicate any pairing between flow versions and React/RN versions.

The way I use flow is by ignoring type errors that come from dependencies. But this only works in versions of flow that use the old error reporting format. [declarations] seems to be the perfect solution but doesn't work at the moment.

I would love to hear from React developers who are able to use Flow successfully. And I would love to find out if I'm missing something.

[sienkashing]

I tried using [declarations] to no avail as well. In the end, when it comes to handling third party flow-typed definitions, I resorted to using flow-typed to do away with the headache of managing incompatible flow definitions.

What I normally do:

1. Ignore .*/node_modules/.* in my .flowconfig file
2. Run flow-typed install for flow-typed to scan my package.json and install all matching type definitions it has
3. Run flow-typed crate-stub <packagename> for packages that are not available.
4. Copy Pasta the type definitions from third party libraries if available into my stubs, or just define the stuff I want type checked as I go along.

Pros:
No more flow errors from third party modules. Yay!

Cons:

1. When adding new packages, gotta manually run flow-typed install <packagename> or flow-typed create-stub <packagename> if it is not available.
2. Gotta manually add type definitions you need into the stubs (you can skip this if you don't care about type checking from third party libraries)

I guess this is similar to using Typescript where you will need to define missing index.d.ts in the node-modules/@types folder for packages that don't have them, but at least flow-typed has some nice tooling to help with generating the basic stuff to get you going.

[jamesisaac]

Hmm yeah weird, [declarations] not seeming effective for me either. It's in the documentation so not sure what the issue is. I've left a comment in the original PR: facebook/flow#4916 (comment)

I think when a project is written with Flow types in the source code itself, there could be benefits to exporting those directly in the repo. They are just guaranteed to be up to date with the code, whereas flow-typed definitions are more of an approximation, not very granular down to individual releases.

I'm also confused on how people are able to use latest versions of Flow successfully with React/React Native. The documentation doesn't seem to indicate any pairing between flow versions and React/RN versions.

I normally go to the branch for the version I'm using on the RN repo, then look at their .flowconfig file, and use the same for my project.

[wcandillon]

@jamesisaac that's a great tip thks 👍🏻

[radex]

I think when a project is written with Flow types in the source code itself, there could be benefits to exporting those directly in the repo. They are just guaranteed to be up to date with the code, whereas flow-typed definitions are more of an approximation, not very granular down to individual releases.

Exactly! This seems so much better than trying to separately maintain the types in an external place...

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.