cmd/compile: gotip cannot infer generic types when functions have no generic parameter

[sina-devel]

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

$ gotip version
go version devel go1.18-62b29b0 Tue Nov 2 17:01:14 2021 +0000 linux/amd64

What did you do?

package main

func zero[T any]() T {
	var o T
	return o
}

func getInt(a int) {}

func zeroInt() int {
	return zero()
}

func main() {
	zeroInt()
	getInt(zero())
}

What did you expect to see?

Successful compilation

What did you see instead?

main.go:11:13: cannot infer T (main.go:3:11)
main.go:17:13: cannot infer T (main.go:3:11)

[ianlancetaylor]

This is working as intended. Inference is based only on function arguments and constraints. See the description at https://go.googlesource.com/proposal/+/refs/heads/master/design/43651-type-parameters.md#type-inference.

[sina-devel]

@ianlancetaylor Ok, and that means it is not possible to add it in future?

[ianlancetaylor]

It is possible to add it in the future. But it would need a clear and precise design for how it works. It should be written as a language change proposal; see https://golang.org/s/proposal. It's not obvious to me how it should work; exactly what types should be inferred if I write zero() + zero() != zero(), and why?

[ianlancetaylor]

If I understand this correctly, it's basically the same as #50285, which is still open.