Fix common prefix completion issue (#2146)

Author: msujew

package-lock.json

@@ -67,7 +67,7 @@
   "dependencies": {
     "@chevrotain/regexp-to-ast": "~12.0.0",
     "chevrotain": "~12.0.0",
-    "chevrotain-allstar": "~0.4.1",
+    "chevrotain-allstar": "~0.4.2",
     "vscode-languageserver": "~9.0.1",
     "vscode-languageserver-textdocument": "~1.0.12",
     "vscode-uri": "~3.1.0"

packages/langium/package.json

@@ -709,4 +709,23 @@ describe('Completion for optional elements', async () => {
         });
     });
 
+    test('Should complete correctly if alternative content is only partially present', async () => {
+        const grammar = `
+            grammar Test
+
+            entry Document: value=(RuleA | RuleB);
+
+            RuleA: 'hello' 'world';
+            RuleB: 'hello' 'world' 'and' 'you';
+
+            hidden terminal WS: /\\s+/;
+        `;
+        const services = await createServicesForGrammar({ grammar });
+        const completion = expectCompletion(services);
+        await completion({
+            text: 'hello world and <|>',
+            index: 0,
+            expectedItems: ['you']
+        });
+    });
 });

packages/langium/test/lsp/completion-provider.test.ts

@@ -11,6 +11,7 @@
       "ES2020",
       "DOM"
     ],
+    "types": ["node"],
     // Generates corresponding '.d.ts' file.
     "declaration": true,
     // Generates a sourcemap for each corresponding '.d.ts' file.