go/types, types2: generic type inference - generic interface input parameter of generic function

[xymon2]

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

$ go version
go version go1.21.1 darwin/arm64

Does this issue reproduce with the latest release?

NO

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

go env Output

$ go env
GO111MODULE='on'
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/godot/Library/Caches/go-build'
GOENV='/Users/godot/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/godot/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/godot/go'
GOPRIVATE='github.com/channel-io/*'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.21.1'
GCCGO='gccgo'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/Users/godot/Desktop/WORK/DEV/chx-backend/go.mod'
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 arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/jx/_3jk95_s41g4q3q50mhll7th0000gn/T/go-build1234621002=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

I tried to compile my project (that used to compile successfully with Go 1.20) but I got an error.

I made a function getting a parameter with generic interface type.

// BoilerModel is generated by sqlboiler - v4.15
func TestFunction[D sqlrepo.DomainModel, B sqlrepo.BoilerModel](
	repo sqlrepo.SQLRepo[D, B],
) {}

Then I called that function like this.

// models.Test is generated by sqlboiler - v4.15
type testRepo struct {
	sqlrepo.SQLRepo[*model.Test, *models.Test]
}

func (repo *testRepo) ErrorFunction() {
	TestFunction(repo.SQLRepo)
}

Result of build is

 cannot infer B 

But go 1.20 builds that code well.
And why only B cannot be inferred?

https://go.dev/play/p/VxOg1KSvJdz
This is playgroud to reproduce that error but it raises error "cannot infer D" not B.

What did you expect to see?

no error as it is with go 1.20

What did you see instead?

 cannot infer B 

[ianlancetaylor]

CC @griesemer

[ianlancetaylor]

@xymon2 can you provide a complete, stand-alone example? Thanks.

[ianlancetaylor]

Oh sorry, just saw the Go playground link. My apologies.

[ianlancetaylor]

This is a case where the interface does not use its type parameters.

type SQLRepo[D DomainModel, B BoilerModel] interface {
	Repo()
}

It's hard to infer a type that isn't used, as really we can infer any type at all. The code does build with go build -gcflags=-lang=go1.20. It should also build if you put go 1.20 in your go.mod file. For 1.21 and later you need to change your code. Sorry.

Closing this issue as a dup of #60377 and #61903. Thanks for reporting it.