The JsonPathDetector class does not handle empty objects correctly

[tetrachromium]

The JsonPathDetector class handles JSON objects and arrays slightly differently, due to the need to recognize an object's property keys. To handle this, the JsonPathDetector state machine uses an additional "pending" state when processing objects. During the "pending" state, no path item has been pushed for properties of the object.

When the closing brace of an empty object is encountered, the state is still "pending" since no properties have been seen. The current implementation of the state machine currently assumes that a path item has been pushed. It therefore incorrectly pops the key of the enclosing object or array.

Consider the following JSON fragment:

{
  "outer": {
    "inner": {
    } // Should have path [ "outer", "inner" ], but has path [ "outer" ]
  }
}

When a JsonPathDetector object encounters the closing brace of the "inner" object, the path is just [ "outer", "inner" ] because no nested properties have been found. Ordinarily the key of the last nested property would be popped, but the "inner" key is popped instead. The JsonChunk is therefore incorrectly given an [ "outer" ] path. The paths of all subsequent JsonChunk objects will then be incorrect.

[tetrachromium]

I have implemented a unit test and fix for this issue, but cannot push it due to insufficient access.

[tetrachromium]

Unit test that illustrates the problem. This test will currently fail.

test("PathDetector handles empty object", async () => {
	const stream = serializeJsonValue({
		outer: {
			inner: {}
		}
	}).pipeThrough(new JsonPathDetector());

	expect(await streamToArray(stream)).toEqual([
		{ ...objectStart(), path: [] },
		{ ...stringStart(StringRole.KEY), path: [] },
		{ ...stringChunk("outer", StringRole.KEY), path: [] },
		{ ...stringEnd(StringRole.KEY), path: [] },
		{ ...colon(), path: [] },
		{ ...objectStart(), path: ["outer"] },
		{ ...stringStart(StringRole.KEY), path: ["outer"] },
		{ ...stringChunk("inner", StringRole.KEY), path: ["outer"] },
		{ ...stringEnd(StringRole.KEY), path: ["outer"] },
		{ ...colon(), path: ["outer"] },
		{ ...objectStart(), path: ["outer", "inner"] },
		{ ...objectEnd(), path: ["outer", "inner"] },
		{ ...objectEnd(), path: ["outer"] },
		{ ...objectEnd(), path: [] }
	]);
});

[tetrachromium]

Pull request #2 has been created to address this issue.

[cdauth]

Brilliant, thanks for the report, the detailed explanation and the fix! I've released v1.2.1 containing the fix.