fix wrong cycle detect by clone the map[visit]int

[alingse]

use visited map[visit]int to check cycle might get some bad case.

the key reason was that, all the pp, p printer share a same map[visit]int

but when we process a struct refer a pointer value twice or more, this is not a cycle, it's just a repeat refer.

maybe use other helper data type for every branch when we call code pp = *p statement

maybe a slice is enough to detect.

branch 1 : [v1, v2, v3, v5]
branch 2 : [v1, v2, v3, v4]
branch 3 : [v1, v2, v3, v4, v1]

only branch3 should print a "CYCLIC REFERENCE"

[alingse]

this is only a draft PR, and i will code more to try fix this. cc @kr

btw, thanks for this great repo.

[kr]

Good catch, thank you! I just opened #96 for the bug itself. That should automatically be closed when this PR gets merged.

[alingse]

cc @kr I have add a clone func to copy the visited map, and add some test about cycle
I test in local go test ./... it successed, need your review and comment if you have some.