github.com/bobg/go-generics/v2/slices: type inference bug?

[bobg]

Getting this error:

type func(a E, b E) bool of less does not match inferred type func(a E, b E) int for func(a E, b E) int

...for code that explicitly declares less as func(a, b E) bool and uses it in a func(a, b E) bool context. Not an int in sight. Details follow.

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

$ go version
go version go1.21.0 linux/amd64

Does this issue reproduce with the latest release?

Yes

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

go env Output

$ go env
GO111MODULE='on'
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/bobg/.cache/go-build'
GOENV='/home/bobg/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/bobg/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/bobg/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.21.0'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/bobg/go/src/github.com/bobg/go-generics/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 -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2985862645=/tmp/go-build -gno-record-gcc-switches'

What did you do?

Checked out the latest version of decouple and ran go vet on it:

$ git clone https://github.com/bobg/decouple.git
$ cd decouple
$ go vet ./...

What did you expect to see?

No output.

What did you see instead?

../../../../pkg/mod/github.com/bobg/go-generics/v2@v2.2.1/slices/dropin.go:150:21: type func(a E, b E) bool of less does not match inferred type func(a E, b E) int for func(a E, b E) int
../../../../pkg/mod/github.com/bobg/go-generics/v2@v2.2.1/slices/dropin.go:156:27: type func(a E, b E) bool of less does not match inferred type func(a E, b E) int for func(a E, b E) int
../../../../pkg/mod/github.com/bobg/go-generics/v2@v2.2.1/slices/dropin.go:167:32: type func(a E, b E) bool of less does not match inferred type func(a E, b E) int for func(a E, b E) int

This refers to these lines in my go-generics module: 150, 156, 167.

These lines are meant to make my slices package be a drop-in replacement for the new Go 1.21 slices package. In each case, my less is declared to be func(a, b E) bool (with E a type parameter), and is passed to a corresponding function in Go's slices, also expecting a func(a, b E) bool. Not an int in sight.

Reproducible after go clean -modcache.

[seankhliao]

Duplicate of #61374

[blackgreen100]

@seankhliao the issue you linked gives 404, please can you update it?