Provider engine panic on explore recursive edge with no parent

[masih]

2022-01-18T14:04:13.499+0200	INFO	provider/engine	engine/linksystem.go:45	Retrieved advertisement from datastore	{"cid": "baguqeeqqj2huagbnkzkxipqqi2j2vce7ya", "size": 958}
panic: Traversed Explore Recursive Edge Node With No Parent

goroutine 153112616 [running]:
github.com/ipld/go-ipld-prime/traversal/selector.ExploreRecursiveEdge.Decide(...)
	/root/code/pkg/mod/github.com/ipld/[email protected]/traversal/selector/exploreRecursiveEdge.go:31
github.com/ipld/go-ipld-prime/traversal/selector.ExploreRecursive.Decide(...)
	/root/code/pkg/mod/github.com/ipld/[email protected]/traversal/selector/exploreRecursive.go:165
github.com/ipld/go-ipld-prime/traversal.Progress.walkAdv(0xc038df92c0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0xc00cfc0310, ...)
	/root/code/pkg/mod/github.com/ipld/[email protected]/traversal/walk.go:159 +0x83
github.com/ipld/go-ipld-prime/traversal.Progress.WalkAdv(0xc038df92c0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0xc00cfc0310, ...)
	/root/code/pkg/mod/github.com/ipld/[email protected]/traversal/walk.go:147 +0xd9
github.com/ipfs/go-graphsync/ipldutil.(*traverser).start.func1(0xc011069900)
	/root/code/pkg/mod/github.com/ipfs/[email protected]/ipldutil/traverser.go:230 +0x3d1
created by github.com/ipfs/go-graphsync/ipldutil.(*traverser).start
	/root/code/pkg/mod/github.com/ipfs/[email protected]/ipldutil/traverser.go:198 +0x55

[masih]

This is an issue in IPLD where a parsed selector can still cause a panic. graphsync does parse the selector before traversal. Until it is guaranteed by IPLD that a parsed selector will not panic consider wrapping provider code with recover to catch any potential panics.