cmd/go: tip breaks program flags in "go run"

[mvdan]

Go version

go version devel go1.22-d73b4322ed Thu Dec 14 22:24:40 2023 +0000 linux/amd64

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

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/mvdan/.cache/go-build'
GOENV='/home/mvdan/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/mvdan/go/pkg/mod'
GONOPROXY='github.com/cue-unity'
GONOSUMDB='github.com/cue-unity'
GOOS='linux'
GOPATH='/home/mvdan/go'
GOPRIVATE='github.com/cue-unity'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/mvdan/tip'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/mvdan/tip/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='devel go1.22-d73b4322ed Thu Dec 14 22:24:40 2023 +0000'
GCCGO='gccgo'
GOAMD64='v3'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
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-build2866565515=/tmp/go-build -gno-record-gcc-switches'

What did you do?

$ go version
go version devel go1.22-d73b4322ed Thu Dec 14 22:24:40 2023 +0000 linux/amd64
$ go run cuelang.org/go/cmd/cue@v0.5.0-beta.5 import -p json
go: -p must be a positive integer: 0
$ /usr/bin/go version
go version go1.21.5 linux/amd64
$ /usr/bin/go run cuelang.org/go/cmd/cue@v0.5.0-beta.5 import -p json
$

What did you expect to see?

Same behavior between Go tip and 1.21; the flag should be passed to the cue program without any error from cmd/go.

What did you see instead?

It seems like cmd/go tries to parse the -p json flag, perhaps not realizing that go run takes an arbitrary number of flags and arguments to pass on to the main package being run:

$ go run -h
usage: go run [build flags] [-exec xprog] package [arguments...]

In my case, import -p json go after the single package argument, so cmd/go should not attempt to parse them.

cc @bcmills I suspect this might be a very recent regression due to https://go-review.googlesource.com/c/go/+/546635. I haven't bisected, but I've also never run into this error before.

[mauri870]

Confirmed that this is a regression from CL 546635. I see that we are also backporting it to go 1.21 in CL550055.

[mauri870]

@bcmills This appears to be enough to fix the issue, but I'm not sure if it is the correct fix:

diff --git a/src/cmd/go/internal/toolchain/select.go b/src/cmd/go/internal/toolchain/select.go
index 84fa7f685c..835d8117cc 100644
--- a/src/cmd/go/internal/toolchain/select.go
+++ b/src/cmd/go/internal/toolchain/select.go
@@ -15,6 +15,7 @@ import (
        "os"
        "path/filepath"
        "runtime"
+       "slices"
        "strconv"
        "strings"

@@ -556,7 +557,15 @@ func goInstallVersion() bool {

        // Make a best effort to parse flags so that module flags like -modcacherw
        // will take effect (see https://go.dev/issue/64282).
-       args := os.Args[2:]
+
+       // All flags past pkg@version should apply to pkg and not to the go
+       // command itself.
+       pkgIdx := slices.Index(os.Args, arg)
+       if pkgIdx == -1 {
+               return false
+       }
+
+       args := os.Args[2:pkgIdx]
        for len(args) > 0 {
                var err error
                _, args, err = cmdflag.ParseOne(cmdFlags, args)

[bcmills]

Thanks for the report! This is a surprising gap in our test coverage. 😅
I'll send a fix today.

[gopherbot]

Change https://go.dev/cl/550237 mentions this issue: cmd/go/internal/toolchain: simplify flag parsing and stop at the first non-flag

[gopherbot]

Change https://go.dev/cl/551215 mentions this issue: cmd/go/internal/toolchain: revert "make a best effort to parse 'go run' and 'go install' flags"