[ES|QL] Open bracket parsing bug (#196241)

## Summary

Closes #191683

Gracefully handles open square brackets in `FROM` command.

### Checklist

Delete any items that are not applicable to this PR.

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

### For maintainers

- [x] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#_add_your_labels)

(cherry picked from commit 3849d99)

packages/kbn-esql-ast/src/parser/__tests__/from.test.ts

@@ -187,5 +187,21 @@ describe('FROM', () => {
 
       expect(errors.length > 0).toBe(true);
     });
+
+    it('when open square bracket "[" is entered', () => {
+      const text = 'FROM kibana_sample_data_logs [';
+      const { errors } = parse(text);
+
+      expect(errors.length > 0).toBe(true);
+      expect(errors[0].message.toLowerCase().includes('metadata')).toBe(true);
+    });
+
+    it('when close square bracket "]" is entered', () => {
+      const text = 'FROM kibana_sample_data_logs []';
+      const { errors } = parse(text);
+
+      expect(errors.length > 0).toBe(true);
+      expect(errors[0].message.toLowerCase().includes('metadata')).toBe(true);
+    });
   });
 });

packages/kbn-esql-ast/src/parser/esql_ast_builder_listener.ts

@@ -120,7 +120,7 @@ export class ESQLAstBuilderListener implements ESQLParserListener {
     const metadataContext = ctx.metadata();
     const metadataContent =
       metadataContext?.deprecated_metadata()?.metadataOption() || metadataContext?.metadataOption();
-    if (metadataContent) {
+    if (metadataContent && metadataContent.METADATA()) {
       const option = createOption(
         metadataContent.METADATA().getText().toLowerCase(),
         metadataContent

x-pack/plugins/security_solution/public/detection_engine/rule_creation_ui/hooks/use_esql_index.test.ts

@@ -27,8 +27,16 @@ describe('useEsqlIndex', () => {
     expect(result.current).toEqual([]);
   });
 
+  it('returns indices which appear in source before syntax error', async () => {
+    const typeErrorCausingQuery = 'from auditbeat* [, auditbeat2*';
+
+    const { result } = renderHook(() => useEsqlIndex(typeErrorCausingQuery, 'esql'));
+
+    expect(result.current).toEqual(['auditbeat*']);
+  });
+
   it('should return empty array if invalid query is causing a TypeError in ES|QL parser', async () => {
-    const typeErrorCausingQuery = 'from auditbeat* []';
+    const typeErrorCausingQuery = 'from []';
 
     const { result } = renderHook(() => useEsqlIndex(typeErrorCausingQuery, 'esql'));