test: #436 add structure guard test for statement isolation

Author: liuxy0551

src/parser/common/basicSQL.ts

@@ -559,6 +559,8 @@ export abstract class BasicSQL<
 
     /**
      * Get the minimum statement tree for collecting completion candidates
+     * Each supported grammar exposes one top-level statement per direct program child
+     * Keep the lookup shallow to avoid selecting nested statements or subqueries
      */
     private getSuggestionParseTree(
         parseTree: ParserRuleContext,
@@ -605,6 +607,7 @@ export abstract class BasicSQL<
 
         if (suggestionParseTree === parseTree) return candidates;
 
+        // Keep the program candidates for outer rule paths and use statement candidates for isolation
         const statementCore = new CodeCompletionCore(parser);
         statementCore.preferredRules = this.preferredRules;
         const statementCandidates = statementCore.collectCandidates(

test/common/suggestion.test.ts

@@ -1,3 +1,5 @@
+import { ParserRuleContext } from 'antlr4ng';
+
 import {
     FlinkSQL,
     GenericSQL,
@@ -20,6 +22,21 @@ const dialects = [
     ['GenericSQL', () => new GenericSQL()],
 ] as const;
 
+test.each(dialects)(
+    '%s exposes each top-level statement as a direct program child',
+    (_, createParser) => {
+        const parseTree = createParser().parse('SELECT * FROM t; SELECT * FROM u');
+        const topLevelStatements =
+            parseTree.children?.filter((child) => child instanceof ParserRuleContext) ?? [];
+
+        expect(topLevelStatements).toHaveLength(2);
+        expect(topLevelStatements.map((statement) => statement.getText())).toEqual([
+            'SELECT*FROMt;',
+            'SELECT*FROMu',
+        ]);
+    }
+);
+
 describe.each(dialects)('%s suggestion at caret position', (_, createParser) => {
     const parser = createParser();