Background: the recursiveiter analyzer reports subtly incorrect definitions of iterators over recursive data structures that lead to poor asymptotic performance. It has been included in gopls for over a year.

It does not trigger very often, but it does report a serious problem with high confidence, and is cheap to run. Here's a typical finding:

    78  func allYamlNodes(n *yaml.Node) iter.Seq[*yaml.Node] {
    79  	return func(yield func(*yaml.Node) bool) {
    80  		if !yield(n) {
    81  			return
    82  		}
    83  		for _, n2 := range n.Content {
    84  			for n3 := range allYamlNodes(n2) { // "inefficient recursion in iterator allYamlNodes"
    85  				if !yield(n3) {
    86  					return
    87  				}
    88  			}
    89  		}
    90  	}
    91  }

More:

• https://go-mod-viewer.appspot.com/github.com/storacha/go-ucanto@v0.7.2/core/delegation/delegation.go#L190
• https://go-mod-viewer.appspot.com/github.com/anacrolix/torrent@v1.61.0/metainfo/file-tree.go#L116
• https://go-mod-viewer.appspot.com/github.com/creachadair/ffs@v0.17.3/storage/monitor/monitor.go#L165

Proposal: we propose to move this analyzer to a public package and include it in the cmd/vet suite.