cmd/go: make go mod download -json return the exit status 0 in case of errors

[perillo]

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

$ go version
go version go1.13.6 linux/amd64

Does this issue reproduce with the latest release?

Yes. But at least with go1.14beta1 go mod download -json does not print debug message on stderr.

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

go env Output

$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN="/home/manlio/.local/bin"
GOCACHE="/home/manlio/.cache/go-build"
GOENV="/home/manlio/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY="github.com/perillo"
GONOSUMDB="github.com/perillo"
GOOS="linux"
GOPATH="/home/manlio/.local/lib/go:/home/manlio/src/go"
GOPRIVATE="github.com/perillo"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build524871395=/tmp/go-build -gno-record-gcc-switches"
GOROOT/bin/go version: go version go1.13.6 linux/amd64
GOROOT/bin/go tool compile -V: compile version go1.13.6
uname -sr: Linux 5.4.15-arch1-1
/usr/lib/libc.so.6: GNU C Library (GNU libc) stable release version 2.30.
gdb --version: GNU gdb (GDB) 8.3.1

What did you do?

go mod download -json github.com/perillo/null
echo $?

In case of errors, the process exit status will be 1, making it more complex to handle the go mod download output.

{
	"Path": "github.com/perillo/null",
	"Error": "module github.com/perillo/null: not a known dependency"
}
1

go mod download -json should return an exit status 0 in case of errors, the same as go list -m -e -json.

[perillo]

There is a similar issue in #35380.

However it suggests to change the documentation. I suggest to change the implementation to match go list -m -e -json. In alternative go mod download should support the -e flag.

[perillo]

I would like to change the issue title.

I think that go mod download should print on stderr the errors encountered, as with go list -json (without the -e flag).

The reason is that the user can simply print the error returned by Command.Run and the content of stderr, instead of processing all the modules and check the Error field.

[perillo]

go mod download has another issue.
The Module.Error field is defined as string instead of *ModuleError as defined in go list -m.
What is the reason for the difference?

[cagedmantis]

@perillo As you mentioned above, there has been a discussion about the original issue mentioned here on #35380. Do you think commenting on that issue would sufficiently help you express your suggested solution?

[perillo]

Yes, thanks.

[cagedmantis]

Great, thank you. Closing this issue.