encoding/json: cyclic maps and slices are not detected

[lujjjh]

The documentation says:

JSON cannot represent cyclic data structures and Marshal does not handle them. Passing cyclic structures to Marshal will result in an error.

However, there are still cases result in an infinite recursion in Go 1.15.

It seems that 64c9ee9 does not handle cyclic maps or slices:

package main

import "encoding/json"

func main() {
	x := map[string]interface{}{}
	x["x"] = x
	json.Marshal(x)
}

and

package main

import "encoding/json"

func main() {
	x := []interface{}{nil}
	x[0] = x
	json.Marshal(x)
}

Originally posted by @lujjjh in #10769 (comment)

[mvdan]

I agree that this is probably a case we missed and should be fixed. Do you want to send a CL?

[gopherbot]

Change https://golang.org/cl/248358 mentions this issue: encoding/json: detect cyclic maps and slices

[eaglexiang]

great, new test case TestSliceNoCycle was created, but why there is no TestSliceCycle now and even no TestPointerCycle in the past.

[lujjjh]

great, new test case TestSliceNoCycle was created, but why there is no TestSliceCycle now and even no TestPointerCycle in the past.

@eaglexiang Thank you for reviewing the code. Since marshalling cyclic structures results in a UnsupportedValueError, these cases are tested in TestUnsupportedValues.

[lujjjh]

I agree that this is probably a case we missed and should be fixed. Do you want to send a CL?

@mvdan I sent a CL last week, but received no feedback.

This is my first time to conribute to Go. What should I do next? Or just wait?

Thank you.

[mvdan]

@lujjjh yes, I was pinged by Gerrit a week ago, and I've seen your ping yesterday on Gerrit and your ping here today. I'm taking some time off this week, or at least trying to. A week is not a long time to wait for a review, especially given that it's August.

I'll likely give a review sometime next week, unless someone beats me to it. But in general, please be a bit patient.