cmd/vet: incorrect printf "invalid argument index" with ... argument

[cherrymui]

What version of Go are you using (go version)?

tip (79669dc)

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

darwin/amd64

What did you do?

https://play.golang.org/p/uIeIGQWBhgB

package main

import (
	"fmt"
)

func main() {
	s := []interface{}{"Hello", "playground"}
	fmt.Printf("%[2]s\n", s...)
}

What did you expect to see?

No vet warning.

I think this is a valid program, which prints "playground" as intended. It doesn't seem like a potential bug to me.

What did you see instead?

./prog.go:9:2: Printf format has invalid argument index [2]

[Matts966]

I sent a patch to fix this problem.
https://go-review.googlesource.com/c/tools/+/192857

[gopherbot]

Change https://golang.org/cl/192857 mentions this issue: analysis/passes/printf: emit linter message related to the index of arguments only when the number of arguments is precise.