Use jest async transformers when available about svelte-jester HOT 21 CLOSED

It seems this is not quite resolved.
I am getting the following error:
Jest: synchronous transformer node_modules/svelte-jester/src/transformer.js must export a "process" function.

"svelte-jester": "2.0.1"
"jest": "27.0.6"
"svelte": "3.41.0"

jest config

 transform: {
    "^.+\\.ts$": "ts-jest",
    "^.+\\.svelte$": [
      "svelte-jester",
      {
        "preprocess": true
      }
    ],
  },

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Support now exists in Jest! However, it hasn't yet been released yet, so we'll need to wait a little in order to be able to use it

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@ritchieanesco #74 was fixed by #75 but that fix hasn't made its way into a released version yet. I don't know why, because 2.1.2 is unusable, so I'd have thought that 2.1.3 would be more urgent. But once 2.1.3 comes out, it will work. I've verified the fix in #75 by cloning the svelte-jester repo and putting "svelte-jester": "../svelte-jester" in my package.json, and then I could successfully use jest.unstable_mockModule in my Svelte unit tests.

So wait for 2.1.3 to come out and it should work for you.

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Jest 27 has just been released. Once my PR #46 has been merged, I will give it a try.

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Extending on a few things @benmccann noted here that I agree with.

If we want to support async transforms and not tie ourselves to Jest versioning, we'll need to support both sync and async transformers for the time being until a reasonable time where we can deprecate sync transformers. We can't force existing codebases using 26.x to upgrade, and if they decide not to upgrade they'll miss bug fixes or any new features. Thus, we need to support both for now.

I'm not sure what the best way will be to determine if async transforms are supported. Ideas include:

* Node environment variable that indicates current Jest version?

* Extracting Jest version from `pacakge.json`?

* Some kind of check for async transformer support?

Keep in mind, it may executed inside a monorepo, and note any existing svelte-jester options that may change final transformation.

From my understanding, we can keep the existing code and just write a new async transformer. I think I already did some steps to extract functionality into seperate files. The only difference will be, how the transformer is called. Either as a subprocess with node or as an async function.

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Awesome thanks for setting this up @benmccann!

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I was just curious @sebastianrothe if this is something you're still planning to give a go of?

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I was just curious @sebastianrothe if this is something you're still planning to give a go of?

I'd love to, but my project at work takes up all my time. I'll try to give it a go at the beginning of next month.

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Looks like this will probably depend on #55. There's a PR for it though: #56

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Extending on a few things @benmccann noted here that I agree with.

If we want to support async transforms and not tie ourselves to Jest versioning, we'll need to support both sync and async transformers for the time being until a reasonable time where we can deprecate sync transformers. We can't force existing codebases using 26.x to upgrade, and if they decide not to upgrade they'll miss bug fixes or any new features. Thus, we need to support both for now.

I'm not sure what the best way will be to determine if async transforms are supported. Ideas include:

• Node environment variable that indicates current Jest version?
• Extracting Jest version from pacakge.json?
• Some kind of check for async transformer support?

Keep in mind, it may executed inside a monorepo, and note any existing svelte-jester options that may change final transformation.

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We can't force existing codebases using 26.x to upgrade

I'm not sure it'd be much of an imposition to ask people to upgrade to v27.x. I just took a look at the breaking changes in v27 and they seem quite minor: https://jestjs.io/blog/2021/05/25/jest-27#features-coming-with-breaking-changes

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I'll be honest I didn't actually look at the breaking changes. There seems to be nothing serious, I was thinking of a few other things outside of the noted breaking changes, but again nothing of importance.

If it all seems okay, we can just ignore what I said and next major version of svelte-jester can simply transition to async only transformers and bump minimum version for Jest in peer deps to >=27.

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I don't understand why we'd want to keep the existing code. Calling as a subprocess with node is purely worse. We should just always return an async transformer

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Well, Jest <27 doesn't understand async transformers. If we rewrite the code, we loose compatibility with Jest 26.x
It is fine to me, but I just wanted to point that out.

Guess, people who need to run Jest 26.x can always use an older version, right.

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Yeah, that's fine. We listed jest >= 27 as a peer dependency:

https://github.com/mihar-22/svelte-jester/blob/1052bed4eb2c3c7c1cc6739ee21363de38f4f7c4/package.json#L46

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Yes, I am seeing same error as @gorjan-mishevski. Same jest config file

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+1. Also same config.

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Please use the latest version: 2.1.2

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@benmccann updating to 2.1.2 now gives me
TypeError: Jest: a transform must export a `process` or `processAsync` function. which was raised in this issue #74. Has this issue regressed?

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I had the same problem as @gorjan-mishevski but 2.1.3 is out now for svelte-jester. I updated jest as well to the currently latest version (27.2.0) and now I get a new error:

Cannot find module './preprocess.js'
Require stack:
      node_modules/svelte-jester/dist/transformer.cjs
      node_modules/@jest/transform/node_modules/jest-util/build/requireOrImportModule.js
      node_modules/@jest/transform/node_modules/jest-util/build/index.js
      node_modules/@jest/transform/build/ScriptTransformer.js
      node_modules/@jest/transform/build/index.js
      node_modules/jest-runtime/build/index.js
      node_modules/@jest/core/build/cli/index.js
      node_modules/@jest/core/build/jest.js
      node_modules/jest/node_modules/jest-cli/build/cli/index.js
      node_modules/jest/node_modules/jest-cli/bin/jest.js
      node_modules/jest/bin/jest.js

      at Object.processSync [as process] (node_modules/svelte-jester/dist/transformer.cjs:115:32)
      at ScriptTransformer.transformSource (node_modules/@jest/transform/build/ScriptTransformer.js:612:31)
      at ScriptTransformer._transformAndBuildScript (node_modules/@jest/transform/build/ScriptTransformer.js:758:40)
      at ScriptTransformer.transform (node_modules/@jest/transform/build/ScriptTransformer.js:815:19)

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I had the same problem as @gorjan-mishevski but 2.1.3 is out now for svelte-jester. I updated jest as well to the currently latest version (27.2.0) and now I get a new error:

Cannot find module './preprocess.js'
Require stack:
      node_modules/svelte-jester/dist/transformer.cjs
      node_modules/@jest/transform/node_modules/jest-util/build/requireOrImportModule.js
      node_modules/@jest/transform/node_modules/jest-util/build/index.js
      node_modules/@jest/transform/build/ScriptTransformer.js
      node_modules/@jest/transform/build/index.js
      node_modules/jest-runtime/build/index.js
      node_modules/@jest/core/build/cli/index.js
      node_modules/@jest/core/build/jest.js
      node_modules/jest/node_modules/jest-cli/build/cli/index.js
      node_modules/jest/node_modules/jest-cli/bin/jest.js
      node_modules/jest/bin/jest.js

      at Object.processSync [as process] (node_modules/svelte-jester/dist/transformer.cjs:115:32)
      at ScriptTransformer.transformSource (node_modules/@jest/transform/build/ScriptTransformer.js:612:31)
      at ScriptTransformer._transformAndBuildScript (node_modules/@jest/transform/build/ScriptTransformer.js:758:40)
      at ScriptTransformer.transform (node_modules/@jest/transform/build/ScriptTransformer.js:815:19)

@n00pper it was left out of the published version but is being addressed 👍
#81

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