Fix the CST after performing assigned actions (#1674)

Author: msujew

packages/langium/src/parser/langium-parser.ts

@@ -342,6 +342,7 @@ export class LangiumParser extends AbstractLangiumParser {
             let last = this.current;
             if (action.feature && action.operator) {
                 last = this.construct();
+                this.nodeBuilder.removeNode(last.$cstNode);
                 const node = this.nodeBuilder.buildCompositeNode(action);
                 node.content.push(last.$cstNode);
                 const newItem = { $type };

packages/langium/test/parser/langium-parser-builder.test.ts

@@ -6,7 +6,7 @@
 
 import type { TokenType, TokenVocabulary } from 'chevrotain';
 import type { AstNode, CstNode, GenericAstNode, Grammar, GrammarAST, LangiumParser, ParseResult, TokenBuilderOptions } from 'langium';
-import { EmptyFileSystem, DefaultTokenBuilder, GrammarUtils } from 'langium';
+import { EmptyFileSystem, DefaultTokenBuilder, GrammarUtils, CstUtils } from 'langium';
 import { describe, expect, test, onTestFailed, beforeAll } from 'vitest';
 import { createLangiumGrammarServices, createServicesForGrammar } from 'langium/grammar';
 import { expandToString } from 'langium/generate';
@@ -926,6 +926,21 @@ describe('Unassigned subrules', () => {
 
 });
 
+describe('Handling hidden nodes', () => {
+    test('Should find comment node of element affected by an assigned action', async () => {
+        const grammar = createLangiumGrammarServices(EmptyFileSystem);
+        const parser = parseHelper(grammar.grammar);
+        const doc = await parser("Test returns string: /** comment 1 */ 'A' | /** comment 2 */  'B' | /** comment 3 */ 'C';");
+        expect(doc).toBeDefined();
+        const value = doc.parseResult.value as Grammar;
+        const ruleDef = value.rules[0].definition as GrammarAST.Alternatives;
+        const a = ruleDef.elements[0];
+        const commentNode = CstUtils.findCommentNode(a.$cstNode, ['ML_COMMENT']);
+        expect(commentNode).toBeDefined();
+        expect(commentNode!.text).toBe('/** comment 1 */');
+    });
+});
+
 describe('Handling EOF', () => {
     test('Use EOF as last part of the entry rule definition', async () => {
         const grammar = `