From 781d365e4c6f4e82c77357d5458d747b89103983 Mon Sep 17 00:00:00 2001
From: Mark Sujew <mark.sujew@typefox.io>
Date: Thu, 19 Sep 2024 11:29:55 +0200
Subject: [PATCH] Perform parser optimizations in production mode

---
 packages/langium-cli/src/generator/module-generator.ts | 6 ++++--
 packages/langium/src/languages/language-meta-data.ts   | 9 +++++++++
 packages/langium/src/parser/langium-parser.ts          | 9 +++++++--
 packages/langium/src/parser/lexer.ts                   | 4 +++-
 4 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/packages/langium-cli/src/generator/module-generator.ts b/packages/langium-cli/src/generator/module-generator.ts
index 2ac6e1981..89789f6d0 100644
--- a/packages/langium-cli/src/generator/module-generator.ts
+++ b/packages/langium-cli/src/generator/module-generator.ts
@@ -5,13 +5,14 @@
  ******************************************************************************/
 
 import type { Grammar, IParserConfig } from 'langium';
-import { type Generated, expandToNode, joinToNode, toString } from 'langium/generate';
+import { EOL, type Generated, expandToNode, joinToNode, toString } from 'langium/generate';
 import type { LangiumConfig, LangiumLanguageConfig } from '../package-types.js';
 import { generatedHeader } from './node-util.js';
 
 export function generateModule(grammars: Grammar[], config: LangiumConfig, grammarConfigMap: Map<Grammar, LangiumLanguageConfig>): string {
     const grammarsWithName = grammars.filter(grammar => !!grammar.name);
     const parserConfig = config.chevrotainParserConfig;
+    const mode = config.mode;
     const hasIParserConfigImport = Boolean(parserConfig) || grammars.some(grammar => grammarConfigMap.get(grammar)?.chevrotainParserConfig !== undefined);
     let needsGeneralParserConfig = undefined;
 
@@ -41,12 +42,13 @@ export function generateModule(grammars: Grammar[], config: LangiumConfig, gramm
             grammarsWithName,
             grammar => {
                 const config = grammarConfigMap.get(grammar)!;
+                const modeValue = mode ? `,${EOL}    mode: '${mode}'` : '';
                 return expandToNode`
 
                     export const ${ grammar.name }LanguageMetaData = {
                         languageId: '${config.id}',
                         fileExtensions: [${config.fileExtensions && joinToNode(config.fileExtensions, e => appendQuotesAndDot(e), { separator: ', ' })}],
-                        caseInsensitive: ${Boolean(config.caseInsensitive)}
+                        caseInsensitive: ${Boolean(config.caseInsensitive)}${modeValue}
                     } as const satisfies LanguageMetaData;
                 `;
             },
diff --git a/packages/langium/src/languages/language-meta-data.ts b/packages/langium/src/languages/language-meta-data.ts
index aa6f5d987..9f6381e3f 100644
--- a/packages/langium/src/languages/language-meta-data.ts
+++ b/packages/langium/src/languages/language-meta-data.ts
@@ -4,8 +4,17 @@
  * terms of the MIT License, which is available in the project root.
  ******************************************************************************/
 
+/**
+ * Metadata of a language.
+ */
 export interface LanguageMetaData {
     languageId: string;
     fileExtensions: readonly string[];
     caseInsensitive: boolean;
+    /**
+     * Mode used to optimize code for development or production environments.
+     * 
+     * In production mode, all lexer/parser validations are disabled.
+     */
+    mode?: 'development' | 'production';
 }
diff --git a/packages/langium/src/parser/langium-parser.ts b/packages/langium/src/parser/langium-parser.ts
index 4d431e3aa..2eb66ce97 100644
--- a/packages/langium/src/parser/langium-parser.ts
+++ b/packages/langium/src/parser/langium-parser.ts
@@ -135,8 +135,10 @@ export abstract class AbstractLangiumParser implements BaseParser {
     constructor(services: LangiumCoreServices) {
         this.lexer = services.parser.Lexer;
         const tokens = this.lexer.definition;
+        const production = services.LanguageMetaData.mode === 'production';
         this.wrapper = new ChevrotainWrapper(tokens, {
             ...services.parser.ParserConfig,
+            skipValidations: production,
             errorMessageProvider: services.parser.ParserErrorMessageProvider
         });
     }
@@ -631,13 +633,16 @@ class ChevrotainWrapper extends EmbeddedActionsParser {
     // This array is set in the base implementation of Chevrotain.
     definitionErrors: IParserDefinitionError[];
 
-    constructor(tokens: TokenVocabulary, config?: IParserConfig) {
+    constructor(tokens: TokenVocabulary, config: IParserConfig) {
         const useDefaultLookahead = config && 'maxLookahead' in config;
         super(tokens, {
             ...defaultConfig,
             lookaheadStrategy: useDefaultLookahead
                 ? new LLkLookaheadStrategy({ maxLookahead: config.maxLookahead })
-                : new LLStarLookaheadStrategy(),
+                : new LLStarLookaheadStrategy({
+                    // If validations are skipped, don't log the lookahead warnings
+                    logging: config.skipValidations ? () => { } : undefined
+                }),
             ...config,
         });
     }
diff --git a/packages/langium/src/parser/lexer.ts b/packages/langium/src/parser/lexer.ts
index fedfad6fc..b387ebcad 100644
--- a/packages/langium/src/parser/lexer.ts
+++ b/packages/langium/src/parser/lexer.ts
@@ -51,8 +51,10 @@ export class DefaultLexer implements Lexer {
         });
         this.tokenTypes = this.toTokenTypeDictionary(tokens);
         const lexerTokens = isTokenTypeDictionary(tokens) ? Object.values(tokens) : tokens;
+        const production = services.LanguageMetaData.mode === 'production';
         this.chevrotainLexer = new ChevrotainLexer(lexerTokens, {
-            positionTracking: 'full'
+            positionTracking: 'full',
+            skipValidations: production
         });
     }