Fix intersecting buckets in strange path expressions

The bucket for the getNextSibling call in DomFacade for `following-sibling::node()[1][self::xxx]` is
not the same as the bucket in the `following-sibling::node()[self::xxx][1]` query

src/parsing/compileAstToExpression.ts

@@ -818,6 +818,7 @@ function pathExpr(ast: IAST, compilationOptions: CompilationOptions) {
 		const children = astHelper.getChildren(step, '*');
 		const postFixExpressions: (['lookup', '*' | Expression] | ['predicate', Expression])[] = [];
 		let intersectingBucket: Bucket = null;
+		let hasSeenNullBucket = false;
 		for (const child of children) {
 			switch (child[0]) {
 				case 'lookup':
@@ -830,10 +831,21 @@ function pathExpr(ast: IAST, compilationOptions: CompilationOptions) {
 							childPredicate,
 							disallowUpdating(compilationOptions)
 						);
-						intersectingBucket = intersectBuckets(
-							intersectingBucket,
-							predicateExpression.getBucket()
-						);
+						if (!hasSeenNullBucket) {
+							const predicateBucket = predicateExpression.getBucket();
+							if (predicateBucket === null) {
+								// If we see a null bucket, we cannot use any future buckets
+								// anymore. This filter may have been position-aware For example:
+								// `following-sibling::node()[1][self::xxx]` is not the same as
+								// `following-sibling::node()[self::xxx][1]`.
+								hasSeenNullBucket = true;
+							} else {
+								intersectingBucket = intersectBuckets(
+									intersectingBucket,
+									predicateBucket
+								);
+							}
+						}
 						postFixExpressions.push(['predicate', predicateExpression]);
 					}
 					break;

test/specs/parsing/getBucketForSelector.tests.ts

@@ -55,4 +55,10 @@ describe('getBucketForSelector', () => {
 	it('returns the correct bucket for text expressions', () => {
 		assertBucketForSelector('self::text()', 'type-3');
 	});
+	it('returns the correct bucket if a filter is position-aware', () => {
+		// Note the axis does not make sense here. But this should work for following-sibling as well
+		assertBucketForSelector('self::node()[1][self::xxx]', null);
+		// The order is changed: this makes it not position-aware
+		assertBucketForSelector('self::node()[self::xxx][1]', 'name-xxx');
+	});
 });