How to extend parsing-only Langium language

[Yokozuna59]

If I have a language that is a parsing-only language, it uses LangiumCoreServices:

sample code

/** Declaration of `Example` services. */
interface ExampleAddedServices {}

/** Union of Langium default services and `Example` services. */
export type ExampleServices = LangiumCoreServices & ExampleAddedServices;

/**
 * Dependency injection module that overrides Langium default services
 * and contributes the declared `Example` services.
 */
export const ExampleModule: Module<
  ExampleServices,
  PartialLangiumCoreServices & ExampleAddedServices
> = {};

How can I extend it so it uses the LangiumServices type with the services in ExampleModule?

---

I tried the following code:

/** Declaration of `Example` lsp services. */
interface ExampleLspAddedServices {}

/** Union of Langium default services and `Example` lsp services. */
export type ExampleLspServices = LangiumServices & ExampleServices & ExampleLspAddedServices;

/**
 * Dependency injection module that overrides Langium default services
 * and contributes the declared `Example` lsp services.
 */
export const ExampleLspModule: Module<
  ExampleLspServices,
  PartialLangiumServices & ExampleLspAddedServices
> = {
  ...ExampleModule,
};

But it throws an error, because the ExampleModule.shared.workspace.TextDocuments types doesn't match:

• LangiumCoreServices:

  langium/packages/langium/src/services.ts

  Line 120 in 7a02166

  TextDocuments?: TextDocumentProvider

• LangiumServices:

  langium/packages/langium/src/lsp/lsp-services.ts

  Line 92 in 7a02166

  TextDocuments: TextDocuments<TextDocument>

I tried to do the following:

export const ExampleLspModule: Module<
  ExampleLspServices,
  PartialLangiumServices & ExampleLspAddedServices
> = {
  ...ExampleModule,
  shared: {
    ...ExampleModule?.shared,
    workspace: {
      ...ExampleModule?.shared?.workspace,
      TextDocuments: undefined,
    },
  },
};

But I can't access the ExampleModule.shared.workspace:

Property 'workspace' does not exist on type 'Module<ExampleLspServices, { ServiceRegistry?: { register?: ((language: LangiumCoreServices) => void) | undefined; getServices?: ((uri: URI) => LangiumCoreServices) | undefined; readonly all?: readonly ({ ...; } | undefined)[] | undefined; } | undefined; workspace?: { ...; } | undefined; AstReflection?: AstReflection...'.
  Property 'workspace' does not exist on type '(injector: ExampleLspServices) => { ServiceRegistry?: { register?: ((language: LangiumCoreServices) => void) | undefined; getServices?: ((uri: URI) => LangiumCoreServices) | undefined; readonly all?: readonly ({ ...; } | undefined)[] | undefined; } | undefined; workspace?: { ...; } | undefined; AstReflection?: AstRef...'.ts(2339)

[msujew]

Hey @Yokozuna59,

you're not supposed to override the shared service instance at all in a language specific service module, since it is set from outside of the module, see here, which is probably why the (pretty cryptic) error message appears. Instead of using the operator on the full ExampleModule, we imagined that adopters would use the API like this:

export const ExampleLspModule: Module<
  ExampleLspServices,
  PartialLangiumServices & ExampleLspAddedServices
> = {
  lsp: {
    completion: () => ... // only override a specific LSP service
  }
};
...
// in the createModule function
const shared = inject(
  createDefaultSharedModule(context),
  ExampleGeneratedSharedModule
);
const example= inject(
  createDefaultModule({ shared }),
  ExampleGeneratedModule,
  ExampleModule, // reuse the non-LSP module here
  ExampleLspModule // add LSP specific modules here
);

Though we can probably document this a bit better. This probably deserves a small guide on our website.

[Yokozuna59]

Hey @msujew,

I have already tried this approach, but it threw an error, so I didn't go with it:

const shared: LangiumSharedServices = inject(
  createDefaultSharedModule(context),
  ExampleGeneratedSharedModule,
);
const ExampleLsp: ExampleLspServices = inject(
  createDefaultModule({ shared }),
  ExampleGeneratedModule,
  ExampleModule, // error here
  ExampleLspModule,
);

Argument of type 'Module<ExampleServices, { Grammar?: { readonly $type?: "Grammar" | undefined; definesHiddenTokens?: boolean | undefined; hiddenTokens?: ({ readonly ref?: AbstractRule | undefined; readonly error?: LinkingError | undefined; readonly $refNode?: CstNode | undefined; readonly $refText?: string | undefined; readonly $nodeDe...' is not assignable to parameter of type 'Module<LangiumDefaultCoreServices & LangiumLSPServices & LangiumGeneratedCoreServices & { Grammar?: { ...; } | undefined; ... 7 more ...; shared?: { ...; } | undefined; } & ExampleAddedServices & { ...; } & ExampleLspAddedServices, { ...; } & ExampleAddedServices>'.
  Types of property 'Grammar' are incompatible.
    Type 'Module<ExampleServices, { readonly $type?: "Grammar" | undefined; definesHiddenTokens?: boolean | undefined; hiddenTokens?: ({ readonly ref?: AbstractRule | undefined; readonly error?: LinkingError | undefined; readonly $refNode?: CstNode | undefined; readonly $refText?: string | undefined; readonly $nodeDescription?: ...' is not assignable to type 'Module<LangiumDefaultCoreServices & LangiumLSPServices & LangiumGeneratedCoreServices & { ...; } & ExampleAddedServices & { ...; } & ExampleLspAddedServices, { ...; } | undefined> | ((injector: LangiumDefaultCoreServices & ... 5 more ... & ExampleLspAddedServices) => { ...; } | undefined)'.
      Type 'Module<ExampleServices, { readonly $type?: "Grammar" | undefined; definesHiddenTokens?: boolean | undefined; hiddenTokens?: ({ readonly ref?: AbstractRule | undefined; readonly error?: LinkingError | undefined; readonly $refNode?: CstNode | undefined; readonly $refText?: string | undefined; readonly $nodeDescription?: ...' is not assignable to type 'Module<LangiumDefaultCoreServices & LangiumLSPServices & LangiumGeneratedCoreServices & { ...; } & ExampleAddedServices & { ...; } & ExampleLspAddedServices, { ...; } | undefined> | ((injector: LangiumDefaultCoreServices & ... 5 more ... & ExampleLspAddedServices) => { ...; } | undefined)'.
        Type 'Module<ExampleServices, { readonly $type?: "Grammar" | undefined; definesHiddenTokens?: boolean | undefined; hiddenTokens?: ({ readonly ref?: AbstractRule | undefined; readonly error?: LinkingError | undefined; readonly $refNode?: CstNode | undefined; readonly $refText?: string | undefined; readonly $nodeDescription?: ...' is not assignable to type 'Module<LangiumDefaultCoreServices & LangiumLSPServices & LangiumGeneratedCoreServices & { Grammar?: { ...; } | undefined; ... 7 more ...; shared?: { ...; } | undefined; } & ExampleAddedServices & { ...; } & ExampleLspAddedServices, { ...; }>'.
          Types of property '$type' are incompatible.
            Type 'Module<ExampleServices, "Grammar" | undefined> | ((injector: ExampleServices) => "Grammar" | undefined)' is not assignable to type 'Module<LangiumDefaultCoreServices & LangiumLSPServices & LangiumGeneratedCoreServices & { ...; } & ExampleAddedServices & { ...; } & ExampleLspAddedServices, "Grammar" | undefined> | ((injector: LangiumDefaultCoreServices & ... 5 more ... & ExampleLspAddedServices) => "Grammar" | undefined)'.
              Type '(injector: ExampleServices) => "Grammar" | undefined' is not assignable to type 'Module<LangiumDefaultCoreServices & LangiumLSPServices & LangiumGeneratedCoreServices & { ...; } & ExampleAddedServices & { ...; } & ExampleLspAddedServices, "Grammar" | undefined> | ((injector: LangiumDefaultCoreServices & ... 5 more ... & ExampleLspAddedServices) => "Grammar" | undefined)'.
                Type '(injector: ExampleServices) => "Grammar" | undefined' is not assignable to type '(injector: LangiumDefaultCoreServices & LangiumLSPServices & LangiumGeneratedCoreServices & { ...; } & ExampleAddedServices & { ...; } & ExampleLspAddedServices) => "Grammar" | undefined'.
                  Types of parameters 'injector' and 'injector' are incompatible.
                    Type 'LangiumDefaultCoreServices & LangiumLSPServices & LangiumGeneratedCoreServices & { Grammar?: { ...; } | undefined; ... 7 more ...; shared?: { ...; } | undefined; } & ExampleAddedServices & { ...; } & ExampleLspAddedServices' is not assignable to type 'ExampleServices'.ts(2345)

[Yokozuna59]

you're not supposed to override the shared service instance at all in a language specific service module...

Is this still the case in multi-language? The default language should have all languages registered in ServiceRegistry:

shared.ServiceRegistry.register(Example);

So it should at least use the shared.ServiceRegistry so it can switch between sub-languages, shouldn't it?

[msujew]

Is this still the case in multi-language? The default language should have all languages registered in ServiceRegistry:

1. There is no "default language".
2. Yes, as all languages share a single instance of the shared services. They are not allowed to instantiate their own shared services. That's why they all are injected through here.
3. The ServiceRegistry is part of the shared services itself, not of any specific language.

I have already tried this approach, but it threw an error, so I didn't go with it:

I can't reproduce that with the example code you've given:

/** Declaration of `Example` services. */
interface ExampleAddedServices {}

/** Union of Langium default services and `Example` services. */
export type ExampleServices = LangiumCoreServices & ExampleAddedServices;

export type ExampleLspServices = LangiumServices & ExampleAddedServices;

export const ExampleModule: Module<ExampleServices, PartialLangiumCoreServices & ExampleAddedServices> = {};

export const ExampleLspModule: Module<ExampleLspServices, PartialLangiumServices & ExampleAddedServices> = {};
...
const example = inject(
  createDefaultModule({ shared }),
  ExampleGeneratedModule,
  ExampleModule, // works fine, no type checking error
  ExampleLspModule
);

Can you link a reproducible repo?

[Yokozuna59]

Thanks.

Can you link a reproducible repo?

No worries, it was an issue because of extending a different module. It's resolved now.