feat: Svelte 5 component class/function interop#2380
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…nents In Svelte 3 and 4, components were classes under the hood, and the base class was `SvelteComponent`. This class was also used in language tools to properly type check the template code. In Svelte 5, components are functions. To give people a way to extend them programmatically, it would be good to expose the actual shape of components. This is why this PR introduces a new `Component` type. For backwards compatibility reasons, we can't just get rid of the old class-based types. We also need to ensure that language tools can work with both the new and old types: There are many libraries out there that provide `d.ts` files with type definitions written using the class types - these should not error. That's why there's an accompagning language tools PR (sveltejs/language-tools#2380) that's doing the heavy lifting: Instead of generating classes, it now generates a constant and an interfaces and uses Typescript's declaration merging feature to provide both so we can declare a component export as being both a class and a function. That ensures that people can still instantiate them with `new` (which they can do if they use the `legacy.componentApi` compiler option), and it also ensure we don't need to adjust any other code generation mechanisms in language tools yet - from a language tools perspective, classes are still the norm. But through exposing the default export as being _also_ callable as a function we can in a future Svelte version, where classes/the Svelte 4 syntax are removed completely, seamlessly switch over to using functions in the code generation, too, and the `d.ts` files generated up until that point will support it because of the dual shape. This way we have both backwards and forwards compatibility.
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…nents In Svelte 3 and 4, components were classes under the hood, and the base class was `SvelteComponent`. This class was also used in language tools to properly type check the template code. In Svelte 5, components are functions. To give people a way to extend them programmatically, it would be good to expose the actual shape of components. This is why this PR introduces a new `Component` type. For backwards compatibility reasons, we can't just get rid of the old class-based types. We also need to ensure that language tools can work with both the new and old types: There are many libraries out there that provide `d.ts` files with type definitions written using the class types - these should not error. That's why there's an accompagning language tools PR (sveltejs/language-tools#2380) that's doing the heavy lifting: Instead of generating classes, it now generates a constant and an interfaces and uses Typescript's declaration merging feature to provide both so we can declare a component export as being both a class and a function. That ensures that people can still instantiate them with `new` (which they can do if they use the `legacy.componentApi` compiler option), and it also ensure we don't need to adjust any other code generation mechanisms in language tools yet - from a language tools perspective, classes are still the norm. But through exposing the default export as being _also_ callable as a function we can in a future Svelte version, where classes/the Svelte 4 syntax are removed completely, seamlessly switch over to using functions in the code generation, too, and the `d.ts` files generated up until that point will support it because of the dual shape. This way we have both backwards and forwards compatibility.
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…nents In Svelte 3 and 4, components were classes under the hood, and the base class was `SvelteComponent`. This class was also used in language tools to properly type check the template code. In Svelte 5, components are functions. To give people a way to extend them programmatically, it would be good to expose the actual shape of components. This is why this PR introduces a new `Component` type. For backwards compatibility reasons, we can't just get rid of the old class-based types. We also need to ensure that language tools can work with both the new and old types: There are many libraries out there that provide `d.ts` files with type definitions written using the class types - these should not error. That's why there's an accompagning language tools PR (sveltejs/language-tools#2380) that's doing the heavy lifting: Instead of generating classes, it now generates a constant and an interfaces and uses Typescript's declaration merging feature to provide both so we can declare a component export as being both a class and a function. That ensures that people can still instantiate them with `new` (which they can do if they use the `legacy.componentApi` compiler option), and it also ensure we don't need to adjust any other code generation mechanisms in language tools yet - from a language tools perspective, classes are still the norm. But through exposing the default export as being _also_ callable as a function we can in a future Svelte version, where classes/the Svelte 4 syntax are removed completely, seamlessly switch over to using functions in the code generation, too, and the `d.ts` files generated up until that point will support it because of the dual shape. This way we have both backwards and forwards compatibility.
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…nents (#11775) In Svelte 3 and 4, components were classes under the hood, and the base class was `SvelteComponent`. This class was also used in language tools to properly type check the template code. In Svelte 5, components are functions. To give people a way to extend them programmatically, it would be good to expose the actual shape of components. This is why this PR introduces a new `Component` type. For backwards compatibility reasons, we can't just get rid of the old class-based types. We also need to ensure that language tools can work with both the new and old types: There are many libraries out there that provide `d.ts` files with type definitions written using the class types - these should not error. That's why there's an accompagning language tools PR (sveltejs/language-tools#2380) that's doing the heavy lifting: Instead of generating classes, it now generates a constant and an interfaces and uses Typescript's declaration merging feature to provide both so we can declare a component export as being both a class and a function. That ensures that people can still instantiate them with `new` (which they can do if they use the `legacy.componentApi` compiler option), and it also ensure we don't need to adjust any other code generation mechanisms in language tools yet - from a language tools perspective, classes are still the norm. But through exposing the default export as being _also_ callable as a function we can in a future Svelte version, where classes/the Svelte 4 syntax are removed completely, seamlessly switch over to using functions in the code generation, too, and the `d.ts` files generated up until that point will support it because of the dual shape. This way we have both backwards and forwards compatibility.
jasonlyu123
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May 29, 2024
packages/language-server/src/plugins/typescript/features/CompletionProvider.ts
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Svelte 5 uses functions to define components under the hood. This should be represented in the types. We can't just switch to using functions though because
d.tsfiles created from Svelte 4 libraries should still work, and those contain classes. So we need interop between functions and classes. The idea is therefore:I had to disable a few tests:
const module = await import(...svelte'); module.defaultanymore when checking for component usages