Expose language metadata as const (#1111)

Exposing the LanguageMetadata as const with satisfies allows the values of
its members like `languageId` or `fileExtensions` to be exposed statically.
This allows for patterns like
```
type MyFileExtensions = typeof MyFancyDSLLanguageMetaData.fileExtensions
```
Where then MyFileExtensions is not typed to a generic `string[]`
but to `['.myDsl']` which makes it easier to avoid mistakes.

Unfortunately this is a breaking change because it requires the fileExtensions
on the LanguageMetaData to be readonly to work.

examples/arithmetics/src/cli/cli-util.ts

@@ -10,7 +10,7 @@ import path from 'path';
 import chalk from 'chalk';
 import { URI } from 'vscode-uri';
 
-export async function extractDocument<T extends AstNode>(fileName: string, extensions: string[], services: LangiumServices): Promise<LangiumDocument<T>> {
+export async function extractDocument<T extends AstNode>(fileName: string, extensions: readonly string[], services: LangiumServices): Promise<LangiumDocument<T>> {
     if (!extensions.includes(path.extname(fileName))) {
         console.error(chalk.yellow(`Please, choose a file with one of these extensions: ${extensions}.`));
         process.exit(1);

examples/arithmetics/src/language-server/generated/module.ts

@@ -7,11 +7,11 @@ import type { LangiumGeneratedServices, LangiumGeneratedSharedServices, LangiumS
 import { ArithmeticsAstReflection } from './ast';
 import { ArithmeticsGrammar } from './grammar';
 
-export const ArithmeticsLanguageMetaData: LanguageMetaData = {
+export const ArithmeticsLanguageMetaData = {
     languageId: 'arithmetics',
     fileExtensions: ['.calc'],
     caseInsensitive: true
-};
+} as const satisfies LanguageMetaData;
 
 export const ArithmeticsGeneratedSharedModule: Module<LangiumSharedServices, LangiumGeneratedSharedServices> = {
     AstReflection: () => new ArithmeticsAstReflection()

examples/domainmodel/src/cli/cli-util.ts

@@ -11,7 +11,7 @@ import path from 'path';
 import chalk from 'chalk';
 import { URI } from 'vscode-uri';
 
-export async function extractDocument<T extends AstNode>(fileName: string, extensions: string[], services: LangiumServices): Promise<LangiumDocument<T>> {
+export async function extractDocument<T extends AstNode>(fileName: string, extensions: readonly string[], services: LangiumServices): Promise<LangiumDocument<T>> {
     if (!extensions.includes(path.extname(fileName))) {
         console.error(chalk.yellow(`Please, choose a file with one of these extensions: ${extensions}.`));
         process.exit(1);
@@ -39,7 +39,7 @@ export async function extractDocument<T extends AstNode>(fileName: string, exten
     return document as LangiumDocument<T>;
 }
 
-export async function extractAstNode<T extends AstNode>(fileName: string, extensions: string[], services: LangiumServices): Promise<T> {
+export async function extractAstNode<T extends AstNode>(fileName: string, extensions: readonly string[], services: LangiumServices): Promise<T> {
     return (await extractDocument(fileName, extensions, services)).parseResult.value as T;
 }
 

examples/domainmodel/src/language-server/generated/module.ts

@@ -7,11 +7,11 @@ import type { LangiumGeneratedServices, LangiumGeneratedSharedServices, LangiumS
 import { DomainModelAstReflection } from './ast';
 import { DomainModelGrammar } from './grammar';
 
-export const DomainModelLanguageMetaData: LanguageMetaData = {
+export const DomainModelLanguageMetaData = {
     languageId: 'domain-model',
     fileExtensions: ['.dmodel'],
     caseInsensitive: false
-};
+} as const satisfies LanguageMetaData;
 
 export const parserConfig: IParserConfig = {
     recoveryEnabled: true,

examples/requirements/src/language-server/generated/module.ts

@@ -7,17 +7,17 @@ import type { LangiumGeneratedServices, LangiumGeneratedSharedServices, LangiumS
 import { RequirementsAndTestsAstReflection } from './ast';
 import { RequirementsGrammar, TestsGrammar } from './grammar';
 
-export const RequirementsLanguageMetaData: LanguageMetaData = {
+export const RequirementsLanguageMetaData = {
     languageId: 'requirements-lang',
     fileExtensions: ['.req'],
     caseInsensitive: false
-};
+} as const satisfies LanguageMetaData;
 
-export const TestsLanguageMetaData: LanguageMetaData = {
+export const TestsLanguageMetaData = {
     languageId: 'tests-lang',
     fileExtensions: ['.tst'],
     caseInsensitive: false
-};
+} as const satisfies LanguageMetaData;
 
 export const RequirementsAndTestsGeneratedSharedModule: Module<LangiumSharedServices, LangiumGeneratedSharedServices> = {
     AstReflection: () => new RequirementsAndTestsAstReflection()

examples/statemachine/src/cli/cli-util.ts

@@ -10,7 +10,7 @@ import chalk from 'chalk';
 import type { AstNode, LangiumDocument, LangiumServices } from 'langium';
 import { URI } from 'vscode-uri';
 
-export async function extractDocument(fileName: string, extensions: string[], services: LangiumServices): Promise<LangiumDocument> {
+export async function extractDocument(fileName: string, extensions: readonly string[], services: LangiumServices): Promise<LangiumDocument> {
     if (!extensions.includes(path.extname(fileName))) {
         console.error(chalk.yellow(`Please, choose a file with one of these extensions: ${extensions}.`));
         process.exit(1);
@@ -38,7 +38,7 @@ export async function extractDocument(fileName: string, extensions: string[], se
     return document;
 }
 
-export async function extractAstNode<T extends AstNode>(fileName: string, extensions: string[], services: LangiumServices): Promise<T> {
+export async function extractAstNode<T extends AstNode>(fileName: string, extensions: readonly string[], services: LangiumServices): Promise<T> {
     return (await extractDocument(fileName, extensions, services)).parseResult?.value as T;
 }
 

examples/statemachine/src/language-server/generated/module.ts

@@ -7,11 +7,11 @@ import type { LangiumGeneratedServices, LangiumGeneratedSharedServices, LangiumS
 import { StatemachineAstReflection } from './ast';
 import { StatemachineGrammar } from './grammar';
 
-export const StatemachineLanguageMetaData: LanguageMetaData = {
+export const StatemachineLanguageMetaData = {
     languageId: 'statemachine',
     fileExtensions: ['.statemachine'],
     caseInsensitive: false
-};
+} as const satisfies LanguageMetaData;
 
 export const StatemachineGeneratedSharedModule: Module<LangiumSharedServices, LangiumGeneratedSharedServices> = {
     AstReflection: () => new StatemachineAstReflection()

packages/langium-cli/src/generator/module-generator.ts

@@ -47,13 +47,13 @@ export function generateModule(grammars: Grammar[], config: LangiumConfig, gramm
     for (const grammar of grammars) {
         if (grammar.name) {
             const config = grammarConfigMap.get(grammar)!;
-            node.append('export const ', grammar.name, 'LanguageMetaData: LanguageMetaData = {', NL);
+            node.append('export const ', grammar.name, 'LanguageMetaData = {', NL);
             node.indent(metaData => {
                 metaData.append(`languageId: '${config.id}',`, NL);
                 metaData.append(`fileExtensions: [${config.fileExtensions && config.fileExtensions.map(e => appendQuotesAndDot(e)).join(', ')}],`, NL);
                 metaData.append(`caseInsensitive: ${Boolean(config.caseInsensitive)}`, NL);
             });
-            node.append('};', NL, NL);
+            node.append('} as const satisfies LanguageMetaData;', NL, NL);
         }
     }
 

packages/langium/src/grammar/generated/module.ts

@@ -10,11 +10,11 @@ import type { IParserConfig } from '../../parser/parser-config';
 import { LangiumGrammarAstReflection } from './ast';
 import { LangiumGrammarGrammar } from './grammar';
 
-export const LangiumGrammarLanguageMetaData: LanguageMetaData = {
+export const LangiumGrammarLanguageMetaData = {
     languageId: 'langium',
     fileExtensions: ['.langium'],
     caseInsensitive: false
-};
+} as const satisfies LanguageMetaData;
 
 export const LangiumGrammarParserConfig: IParserConfig = {
     maxLookahead: 3,

packages/langium/src/grammar/language-meta-data.ts

@@ -6,6 +6,6 @@
 
 export interface LanguageMetaData {
     languageId: string;
-    fileExtensions: string[];
+    fileExtensions: readonly string[];
     caseInsensitive: boolean;
 }