cmd/vet: printfunc false negative on struct without String method #17798
Description
package main
import "fmt"
type T int
func (T) String() string { return "T" }
type S struct {
t T
}
func main() {
var t T
fmt.Printf("%s\n", t)
var s S
fmt.Printf("%s\n", s)
}$ go tool vet x.go
$ go run x.go
T
{%!s(main.T=0)}vet should know that S isn't a fmt.Stringer. The printfunc's "satisfies interface" check needs improvements. Related is #17057.