proposal: cmd/vet: reject unary min and max calls

[dsnet]

Proposal Details

A unary min and max call is an identity function and its presence suggests a bug.

I had code that was doing the following:

blockSize = min(max(r.minBlockSize, blockSize, r.maxBlockSize))

where the intent is to clamp blockSize within a certain range.

However, due to a single misplaced ), this does not work.
It should have been:

blockSize = min(max(r.minBlockSize, blockSize), r.maxBlockSize)

I propose that go vet flag any unary calls to min or max, which would have caught my bug where I had 3 arguments passed to max, but only 1 argument passed to min.

[ianlancetaylor]

CC @golang/tools-team

[leaxoy]

Maybe I don't have relevant contextual information, why is the max function allowed to accept a parameter, and what is its actual meaning? Is there any real scenario where only one parameter needs to be passed?

[seankhliao]

the function signature is max[T cmp.Ordered](x T, y ...T) T

[zigo101]

@leaxoy

why is the max function allowed to accept a parameter, and what is its actual meaning? Is there any real scenario where only one parameter needs to be passed?

At least, min/max can be used as poor men's eval of ordered expressions. For example,
in the following code, the foo call may return 3 or 4, but the bar call is guaranteed to return 3.

package main

func foo(k int) int {
	f := func() int {
		k++
		return k
	}
	return k + f()
}

func bar(k int) int {
	f := func() int {
		k++
		return k
	}
	return min(k) + f()
}

func main() {
	println(foo(1), bar(1))
}

:D

Similarly, append can be used poor men's eval of slice expressions: https://go.dev/play/p/9T0KcZaYtuY

[adonovan]

This seems closely analogous to #60448, which added a similar vet check for append. (Too bad we called it append and not missingarg or something more general...)

[AlexanderYastrebov]

Maybe I don't have relevant contextual information, why is the max function allowed to accept a parameter, and what is its actual meaning? Is there any real scenario where only one parameter needs to be passed?

This was raised during discussion #59488 (comment) and there was no obvious reason to prohibit it #59488 (comment)
Now there is a reason.