cmd/go: stdversion check should be on by default for `go test`

[mvdan]

env GOTOOLCHAIN=go1.26.0
exec go version

exec go run .
exec go test
exec go vet

-- go.mod --
module test

go 1.25.0
-- main.go --
package main

import "bytes"

func main() { var _ = (*bytes.Buffer).Peek }
-- main_test.go --
package main_test

import "testing"

func TestDummy(t *testing.T) {}

> env GOTOOLCHAIN=go1.26.0
> exec go version
[stdout]
go version go1.26.0 linux/amd64
[stderr]
go: downloading go1.26.0 (linux/amd64)
> exec go run .
> exec go test
[stdout]
PASS
ok  	test	0.001s
> exec go vet
[stderr]
main.go:5:39: bytes.Peek requires go1.26 or later (file is go1.25)
[exit status 1]

It's a shame that go test doesn't surface this problem; even though go vet and gopls do surface it loudly, the sooner the user can correct this problem, the better. Otherwise they could later on find themselves in a situation where they have to rewrite code to stop using new APIs or language features.

I also wonder why this check wasn't added to go test once it was introduced; it seems like a simple (and presumably fast) check that should have zero false negatives. I imagine there are other similar checks that would be a good addition as well.

Split from #77653 (comment).

[gabyhelp]

Related Issues

• cmd/vet: report use of too-new standard library symbols #46136 (closed)
• cmd/vet: disable checks based on go.mod go version #57063
• x/tools/go/analysis/passes/stdversion: language vs toolchain version #68246
• cmd/go: missing version diagnostic when a package in the main module imports a package from a newer release #48966 (closed)
• cmd/go: set the Go Version for command-line files to be the containing module's Go Version #68159

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[dmitshur]

I also wonder why this check wasn't added to go test once it was introduced; it seems like a simple (and presumably fast) check that should have zero false negatives.

I noticed that the accepted proposal to introduce the check (https://go.dev/design/46136-vet-std-references) confirms that adding it to go test too was intended, and contains an explanation for why it wasn't done right away:

With this proposal, go vet (and go test) would report an error if [...]

This analysis should have no false positives, so it may be enabled by default in go test.

We may want to add this analysis to go vet without immediately enabling it by default in go test. While it should be safe to enable in go test (no false positives), we‘ll need to verify this is actually the case, and we’ll need to understand how common these errors will be.