cmd/go: 'go get' in a module with a higher go version may leave go.(mod|sum) in bad state

[myitcv]

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

$ go version
go version go1.16.13 linux/arm64

Does this issue reproduce with the latest release?

The latest go1.16 version, yes.

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

go env Output

$ go env
GO111MODULE="on"
GOARCH="arm64"
GOBIN=""
GOCACHE="/home/myitcv/.cache/go-build"
GOENV="/home/myitcv/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/myitcv/gostuff/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/myitcv/gostuff"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/myitcv/gos"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/myitcv/gos/pkg/tool/linux_arm64"
GOVCS=""
GOVERSION="go1.16.13"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/myitcv/gostuff/src/github.com/myitcv/govim/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build4113847066=/tmp/go-build -gno-record-gcc-switches"

What did you do?

# git checkout
exec git init
exec git remote add origin https://github.com/govim/govim
exec git fetch origin 1da33d23886a18dd8280770dad0d3ae60e872e6a
exec git checkout FETCH_HEAD

# go version check
go version

# get new versions of tools and gopls
go get golang.org/x/tools/gopls@v0.0.0-20220131221016-263785d77403 golang.org/x/tools@v0.1.10-0.20220131221016-263785d77403

# try and tidy
go mod tidy

# go generate again
go generate . ./cmd/govim

The go mod tidy step fails with:

go mod tidy: go.mod file indicates go 1.17, but maximum supported version is 1.16

The go generate step fails with:

go: downloading gopkg.in/tomb.v2 v2.0.0-20161208151619-d5d1b5820637
go: downloading github.com/fsnotify/fsnotify v1.4.7
govim.go:21:2: missing go.sum entry for module providing package github.com/kr/pretty (imported by github.com/govim/govim); to add:
        go get github.com/govim/govim
internal/cmd/genconfig/genconfig.go:15:2: missing go.sum entry for module providing package github.com/rogpeppe/go-internal/semver (imported by github.com/govim/govim/internal/cmd/genconfig); to add:
        go get github.com/govim/govim/internal/cmd/genconfig
govim.go:26: running "go": exit status 1
../../internal/cmd/txtarutil/main.go:39:2: missing go.sum entry for module providing package github.com/rogpeppe/go-internal/txtar (imported by github.com/govim/govim/internal/cmd/txtarutil); to add:
        go get github.com/govim/govim/internal/cmd/txtarutil
cmd/govim/main_test.go:30: running "go": exit status 1

(which is odd because the main module is github.com/govim/govim)

What did you expect to see?

It strikes me that the go get step should probably have failed in the first instance, because it couldn't make the necessary changes to go.(mod|sum) to leave both in a valid state.

What did you see instead?

go.(mod|sum) in a bad state that can't be corrected.

[bcmills]

Hmm, interesting. Yeah, it may be that go get itself should fail when the go version is higher than supported, since it doesn't in general know how to maintain invariants for higher versions.

(CC @matloob)

[thepudds]

Is this a more specific instance of #50468?

(FWIW, I think I might have hit this too switching back and forth between Go 1.17 and tip).

[bcmills]

Duplicate of #50468