cmd/compile: //go:build file version ignored when calling generic fn which has related type params (reproduces with 1.21 and 1.20, not at tip)

[corhere]

Go version

go version go1.21.5 darwin/amd64

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

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/Users/corysnider/Library/Caches/go-build'
GOENV='/Users/corysnider/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Volumes/Workspace/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Volumes/Workspace'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/Cellar/go/1.21.5/libexec'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/Cellar/go/1.21.5/libexec/pkg/tool/darwin_amd64'
GOVCS=''
GOVERSION='go1.21.5'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/8p/tzn5bkn967vfgttpr2d2kpjm0000gq/T/go-build2320458225=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

$ cat repro.go
//go:build go1.18

package repro

func genericfn[S ~[]E, E any](s S) S {
	return s
}

func do() []string {
	return genericfn([]string{})
}
$ go tool compile -lang=go1.16 repro.go

What did you expect to see?

Compilation succeeds. It succeeds with go version devel go1.22-b60bf8f8e1 Fri Dec 15 19:35:21 2023 +0000 darwin/amd64.

What did you see instead?

embedding interface element ~[]string requires go1.18 or later (-lang was set to go1.16; check go.mod)

[mdempsky]

This looks like a typechecker issue. My understanding of 804d786's commit message is that this should be valid. (Not sure if there's more permanent documentation describing the expected behavior here; for example, I don't see any mention of the backwards compatibility logic for M >= 21 at https://pkg.go.dev/cmd/go. /cc @rsc)

/cc @griesemer @findleyr

[griesemer]

I cannot reproduce this. With

$ go version
go version go1.22rc1 darwin/amd64

and x.go:

$ cat x.go
//go:build go1.18

package repro

func genericfn[S ~[]E, E any](s S) S {
	return s
}

func do() []string {
	return genericfn([]string{})
}

compilation succeeds:

$ go tool compile -lang=go1.16 x.go
$

To double-check, I added a print statement in the relevant code section, and it does indeed select go1.18 for that file.

Please verify that you are indeed using a new compiler version.
I'm going to close this for now. Feel free to re-open if you have additional evidence, thanks.

[corhere]

@griesemer I know that Go 1.22 is not affected. I said as much in the issue report. The issue is reproducible on Go 1.21.5.

[griesemer]

@corhere Ah. Apologies for not reading more carefully.

Hm, the relevant code didn't exist for 1.21.5 I believe. Not sure if we can easily/should backport.

Reopening, to determine next steps.