fix(create-vite): update template-lit-ts tsconfig (fix #12854)

[augustjk]

Description

Fixes #12854
Updates tsconfig settings to be compatible with Lit projects.
Context for settings: https://lit.dev/docs/components/decorators/#decorators-typescript

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[ArnaudBarre]

Is this still valid with TS 5?
This flag is now kind of deprecated: https://devblogs.microsoft.com/typescript/announcing-typescript-5-0/#differences-with-experimental-legacy-decorators

Same for useDefineForClassFields, this flag enforce using a more spec compliant compilation, which I think is good. Unless crucial feature of the framework doesn't work without it, I would be against having empty templates that put you in a situation where code doesn't follow the spec.

[redfox-mx]

Hi, I think this options must be keep since esbuild is not a full spec typescript compiler. By other hand, Lit docs really recommend this options to be setted.

Why? Currently, lit uses old decorators style since it uses typescript 4.7. useDefineForClassFields is more importan than decorators because lit uses property accesors to keep track of reactivity system, and old options brake it.

[bluwy]

I'm fine with this if it's what the lit docs recommend.

[ArnaudBarre]

I personally feels bad to ship empty templates with legacy/deprecated options turn on. If decorators are not a required part of the framework, I would advice people to not start using this legacy runtime behaviour that will never be shipped to engines. Is this legacy requirement tracked as an issue on the framework side?

[augustjk]

Lit does plan to implement the new decorators eventually but we require decorator metadata to be implemented microsoft/TypeScript#53461 for feature parity with our existing decorators.

While technically decorators are not a required part of the framework, most Lit projects using TS will be using decorators as they are prevalent in the official docs and examples as well.

I do understand the hesitation of including legacy/deprecated settings for templates. However, per the TS 5.0 blog

--experimentalDecorators will continue to exist for the foreseeable future

I believe it's valid to include this flag for projects that have relied on this feature for so long. And these flag requirements are documented in the Lit docs as mentioned above.

As it is, https://vite.new/lit-ts leads to a non-functioning project.

[ArnaudBarre]

Thanks for the update and the pointer.

For more context on my initial pushback, I think we have a great chance in the ecosystem to have access to fast transpiler like esbuild and I think we should try to stay away from TS features that are more than syntax transformation to be able to use these new transpilers.