https://go.dev/play/p/p5A4mFaqogQ creates a synthetic syntax tree representing <-(<-chan int)(nil). The go/format printer renders this as <-<-chan int(nil), which parses to a different tree--a receive of a receive--that doesn't type check because the channel value is int. (If instead we had used <-<-chan chan int(nil), the result would type check but would have a different meaning.) The parser creates a ParenExpr around the type so the problem doesn't show up in gofmt, but only in refactoring tools that create syntax trees programmatically.

I think this is a bug in the printer, and that it should emit parens.