legacy decorators + preset-env issue

[Windvis]

The babel-plugin-proposal-decorators docs mention that you don't need the @babel/plugin-transform-class-properties and @babel/plugin-private-methods plugins if you are using @babel/preset-env.

If you are already using @babel/preset-env, you can safely remove @babel/plugin-transform-class-properties and @babel/plugin-private-methods:

I'm trying to remove those plugins from the ember-cli-babel package since it also uses preset-env, but I'm seeing the following runtime exception:

Decorating class property failed. Please ensure that transform-class-properties is enabled and runs after the decorators transform.

Which seems to get added here:

babel/packages/babel-plugin-proposal-decorators/src/transformer-legacy.ts

Lines 221 to 224 in 5ebab54

	node.value = t.callExpression(
	state.addHelper("initializerWarningHelper"),
	[descriptor, t.thisExpression()],
	);

It does work if I configure the targets to a version that requires the class fields to be transpiled.

Is the information in the documentation incorrect or am I doing something wrong? I tried reproducing it in the repl, but I'm not sure if the legacy decorators transform can be enabled there.

Version information:

• @babel/core: 7.22.11
• @babel/preset-env: 7.22.10
• @babel/plugin-proposal-decorators: 7.22.10

Any insights are appreciated, thanks!

[JLHwung]

The legacy decorators transform relies on the class properties / private methods transform and we have no plan to bring any feature update to that legacy mode. From now on, you have two choices:

1. migrate to the stage-3 decorator version: "2023-05", which is designed to work without class elements transform. And both Babel and TS 5.0 support it well, unlike legacy decorator where they have different behaviour.
2. manually include the class elements transform with the legacy decorators

However, we should update the docs to note that you can safely remove those plugins only if you are using the stage 3 decorator transforms.

[Windvis]

Thanks for the information, that makes sense 👍.

[Windvis]

However, we should update the docs to note that you can safely remove those plugins only if you are using the stage 3 decorator transforms.

It's especially confusing since that information is under the "legacy" option as well 😄.

[JLHwung]

Yes I agree, I am drafting a docs PR to address that.

[JLHwung]

Docs PR: babel/website#2818, feel free to leave comments there if you have any further questions.