testing: go test -n is missing the creation of _testmain.go

[Snaipe]

Go version

go1.21.5

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/snaipe/.local/var/cache/go-build'
GOENV='/home/snaipe/.local/etc/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/snaipe/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/snaipe/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/lib/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/lib/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.21.5'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/snaipe/b5/src/barney.ci/golang/generator/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-build859927413=/tmp/go-build -gno-record-gcc-switches'

What did you do?

Running the following commands:

$ go test -a -n 2>build.sh
$ WORK=/tmp/go-test envsubst '$WORK' <build.sh >build-exp.sh
$ sh -xe ./build-exp.sh </dev/null

... should reproduce the same effect as running go test normally.

What did you see happen?

The command building the test binary fails to find _testmain.go

+ /usr/lib/go/pkg/tool/linux_amd64/compile -o /tmp/go-test/b001/_pkg_.a -trimpath /tmp/go-test/b001=> -p main -complete -buildid yj7N4yan_zFjBd_JXc9h/yj7N4yan_zFjBd_JXc9h -dwarf=false -goversion go1.21.5 -c=4 -nolocalimports -importcfg /tmp/go-test/b001/importcfg -pack /tmp/go-test/b001/_testmain.go
open /tmp/go-test/b001/_testmain.go: no such file or directory

What did you expect to see?

The compile command should have succeeded.

This is happening because the writing of the _testmain.go file is directly done by go test rather than done via an action.

[gopherbot]

Change https://go.dev/cl/574698 mentions this issue: cmd/go/internal/test: write _testmain.go with -n flag

[thanm]

@golang/tools-team

I am not sure it makes sense to have a strong commitment to ensuring that "go build/test -n" output produces a script that has the exact same semantics as the build itself - I am sure I have seen other places similar to this where the trace output is not perfectly reflective of reality.

If we want to do this we would need a lot more testing, perhaps a builder that would lock down this behavior (otherwise it would break as the Go tool evolved). This doesn't seem (at least to me) like a good use of team resources. Go tools folks should have the final call however.

[matloob]

@thanm I agree that it shouldn't be a super high priority for us to ensure the script is perfect, but -n is a feature of go build/test that we say we support in the documentation, so it seems to me that we should try to make an effort to keep it accurate?

edit: I can see the argument in the other direction-- the help test says that we print the commands run, and I guess it's debatable whether producing the testmain file is one of the "commands" that we run, but we seem to print out entries for the other inputs that we produce to the other commands.

[thanm]

@matloob that works for me-- if you and the other Go command owners are happy with the proposed fix so am I, thanks :-)

[matloob]

Sounds good. We'll move forward with the review.