go build generics backwards compatibility

[pconstantinou]

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

1.21.0

Does this issue reproduce with the latest release?

Yes, it was introduced with 1.21.

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

go env Output

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/phil/.cache/go-build'
GOENV='/home/phil/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/phil/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/phil/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/phil/go/src/github.com/automaticCRM/memdb/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-build3575205802=/tmp/go-build -gno-record-gcc-switches'

What did you do?

My code that compiled under go 1.20 with generics fails to compile with go 1.21.

Error message:

../../csvctd/ctdcsv.go:324:47: type func(a model.HumanCompanyRole, b model.HumanCompanyRole) bool of func(a, b model.HumanCompanyRole) bool {…} does not match inferred type func(a model.HumanCompanyRole, b model.HumanCompanyRole) int for func(a E, b E) int

       var companyContactRelationships []model.HumanCompanyRole = ....
       slices.SortFunc(companyContactRelationships, func(a, b model.HumanCompanyRole) bool {
                return a.Company.CompanyName < b.Company.CompanyName &&
                        a.CompanyRole.Title < b.CompanyRole.Title &&
                        a.CompanyRole.WhenEnded < b.CompanyRole.WhenEnded &&
                        a.CompanyRole.IsCurrent && a.CompanyRole.IsCurrent != b.CompanyRole.IsCurrent &&
                        a.CompanyRole.WhenStarted < b.CompanyRole.WhenStarted
        })

What did you expect to see?

I expected backward compatibility.

What did you see instead?

Compile errors.

[seankhliao]

slices was in golang.org/x/exp, there was no stability guarantee for that
you were also not up to date on x/exp for it to break.

[AlekSi]

See also: #61374