#82 but with babel options

[TikiTDO]

Continuing from #82, with more generic handling...

What: Allows preval to parse typescript (and potentially any dialect supported by babel with some extra work)

Why: Preval currently chokes on typescript.

This PR serves as a proof-of-concept to show that a TS file can be transformed into plain JS before being handed off the the require-from-string helper.

This could be generalized with a more extensive set of transformers, or potentially even a babel option for the plugin to allow an arbitrary set of extra plugins.

How: Check for typescript files when parsing a @preval tagged file, and optionally parse it with the typescript transformer enabled.

Note, this example only handled the file comment approach, since that code already used babel for parsing the input file. Expanding this it to support the other three approaches would require some changes to use babel handlers such as transformFileSync or transformSync

[TikiTDO]

@kentcdodds In terms of babel options, I was just thinking something like this. Fairly simple, but gives users complete control of how to parse the code they would like to preval.

[codecov[bot]]

Codecov Report

Merging #83 into master will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #83   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            4         4           
  Lines          106       109    +3     
  Branches        22        25    +3     
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+ Hits           106       109    +3     

Impacted Files	Coverage Δ
src/index.js	100.00% <100.00%> (ø)

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[TikiTDO]

I added an example of how you might use this for typescript.

[TikiTDO]

The component API is currently the only one that currently uses the babel parser, and it's the only one I actively use.

Looking at the other ones, it should be pretty straight forward to use the transform or transformSync method to also add this functionality to the other two scenarios. However it's not something I've verified so I want to make sure you're ok with this approach before I spend time on getting those working too.

If you're happy with this approach I can see about normalizing the approach for all three of them.

[kentcdodds]

I am. Thank you so much for working on this @TikiTDO :) I think normalizing it would be a good idea.

[TikiTDO]

I tried adding a transform call conditional on having the prevalBabelOptions option. I seems to work (or at least it seems to not break existing scenarios), though a full test would require actually testing with a real plugin.

I will need to come back to it tomorrow to double check everything, and generalize the readme.

[lencioni]

@TikiTDO Thanks for your work on this so far! I am working in a codebase that we are trying to convert completely to TypeScript, and I think this PR might help me out. Have you had any luck double-checking and generalizing the readme?

[TikiTDO]

Oh wow, sorry, totally forgot about this.

With the changes in this PR, the config passed to prevalBabelOptions should get passed into all the transform calls, so it's a matter of finding the correct set of plugins necessary to fully parse and transform your code. Most of the challenge comes from figuring out which set of plugins actually results in a viable result. If you specify the wrong set it will give you code which will make requireFromString choke.

I have a mountain of work today, but I'll leave a tab open and hopefully remember to come back to it in the evening / over the weekend.

[lencioni]

I've built this version and pushed it up here so I could more easily install it and try it out in my codebase: https://github.com/lencioni/babel-plugin-preval/commit/cd9e6d0daebc2b3996fc88927b71f8ab8edcdc50

I installed it by running

yarn add https://github.com/lencioni/babel-plugin-preval#cd9e6d0daebc2b3996fc88927b71f8ab8edcdc50

And then I configured it like this:

      "plugins": [
        [
          "preval",
          {
            "prevalBabelOptions": {
              "presets": [
                "@babel/typescript",
                "@babel/preset-env",
                {
                  "targets": {
                    "node": true
                  },

                  "modules": true,
                  "bugfixes": true
                }
              ],

              "plugins": [
                "inline-json-import",
                "@babel/plugin-transform-modules-commonjs",
              ]
            }
          }
        ]

I've tried it with a few other settings as well, but I can't seem to get it to work. I just end up with errors like

SyntaxError: Cannot use import statement outside a module

or

SyntaxError: Unexpected token 'export'

I expected either the preset-env or the plugin-transform-modules-commonjs to cover this, but it doesn't seem to be taking effect. Did I mess it up?

[TikiTDO]

That looks familiar. I could never get it working with @babel/preset-env. It tries to do a lot of magic that isn't necessarily useful.

Had to use these two plugins, without any presets:

"@babel/plugin-transform-typescript", "@babel/plugin-transform-modules-commonjs"

[TikiTDO]

Those two plugins worked for this snippet:

// @preval
import { country } from "iso-3166-2"

export default ["CA", "US"].reduce<{ [key: string]: Array<{ code: string; name: string }> }>(
  (acc, countryCode) => {
    acc[countryCode] = Object.entries((country(countryCode) || { sub: [] }).sub)
      .map(([key, value]) => ({ code: key.split("-")[1], name: value.name }))
      .sort((first, second) => {
        const firstProv = first.name.toLowerCase()
        const secondProv = second.name.toLowerCase()
        if (firstProv < secondProv) {
          return -1
        } else if (firstProv > secondProv) {
          return 1
        } else {
          return 0
        }
      })
    return acc
  },
  {},
)

[lencioni]

Yeah, those two plugins are one of the combos I tried, but got the same result. This is my entire file that I'm testing it on:

// @preval

import '../../../private/babelHelpersForPreval';

I wonder if my build or yarn install didn't get your changes somehow...