cmd/go: go test -c does not accept -o $dir

[bcmills]

Since Go 1.14 (#14295), go build -o $dir ./... has allowed one to build multiple packages and write their executables to a directory.

Since go test -c is closely analogous to go build, I expected it to be able to do the same. However, it does not:

~/src/golang.org/x/mod$ go build -o "$(mktemp -d)/" ./...

~/src/golang.org/x/mod$ go test -c -o "$(mktemp -d)/" ./...
cannot use -c flag with multiple packages

~/src/golang.org/x/mod$ go version
go version devel go1.21-a106defdda Fri Jan 27 15:28:30 2023 +0000 linux/amd64

~/src/golang.org/x/mod$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/usr/local/google/home/bcmills/.cache/go-build"
GOENV="/usr/local/google/home/bcmills/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/usr/local/google/home/bcmills/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/usr/local/google/home/bcmills"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/google/home/bcmills/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/google/home/bcmills/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="devel go1.21-a106defdda Fri Jan 27 15:28:30 2023 +0000"
GCCGO="/usr/local/google/home/bcmills/bin/gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="c++"
CGO_ENABLED="1"
GOMOD="/usr/local/google/home/bcmills/src/golang.org/x/mod/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 -fdebug-prefix-map=/tmp/go-build2157072955=/tmp/go-build -gno-record-gcc-switches"

[bcmills]

The same holds for os.DevNull:

~/src/golang.org/x/mod$ go build -o /dev/null ./...

~/src/golang.org/x/mod$ go test -c -o /dev/null ./...
cannot use -c flag with multiple packages

[maksadbek]

@bcmills
Should the -o $dir flag generate one executable file for all packages or multiple executables for each package ?

[seankhliao]

dup of #15513 ?

[bcmills]

Duplicate of #15513