modules: "updates to go.mod needed" when I test 1.20 code using 1.21+

[AndreasBergmeier6176]

Go version

go version go1.22.0 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''                                                                                                                                            
GOARCH='amd64'                                                                                                                                            
GOBIN=''                                                                                                                                                  
GOCACHE='/root/.cache/go-build'
GOENV='/root/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.22.0'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='0'
GOMOD='/app/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 -fno-caret-diagnostics -Qunused-arguments -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build405843297=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I have 1.20 code (as expressed in go.mod).
Tried testing inside golang:1.22-alpine Container:

FROM golang:1.22-alpine AS build

ENV CGO_ENABLED=0
WORKDIR /app

COPY go.* ./

RUN --mount=type=cache,target=/root/go/pkg/mod go mod download

COPY . ./

RUN --mount=type=cache,target=/root/.cache/go-build \
    --mount=type=cache,target=/root/go/pkg/mod \
    go build -o /service cmd/*.go

RUN --mount=type=cache,target=/root/.cache/go-build \
    --mount=type=cache,target=/root/go/pkg/mod \
    go test ./... -v

Same happens with golang:1.21-alpine.

What did you see happen?

go build works fine. go test fails with:

go: updates to go.mod needed; to update it:

Aside from the very obscured reason why it needs to be updated - it only happens if I choose 1.21 or 1.22 Golang.
I was under the impression that 1.20 code should build/test with newer versions.

What did you expect to see?

It should build/test using 1.21/1.22 without any change to go.mod.

[seankhliao]

this is working as intended, starting 1.21 go started enforcing minimum go versions like any other dependency.

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For questions please refer to https://github.com/golang/go/wiki/Questions

[AndreasBergmeier6176]

Don't you think it would be better to state that compat. change then in the error message?
Why not then in this case replace go: updates to go.mod needed; to update it: with e.g.:

go: Version in go.mod (1.20) does not match Version of executable (1.21).
Upgrade go.mod to version 1.21.
Exact Go Version matching is enforced from Go 1.21 onward.