cmd/go: clean on module uses directory name

[DeedleFake]

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

go version go1.11rc1 darwin/amd64

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

GOARCH="amd64"
GOBIN=""
GOCACHE="$HOME/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="$HOME/go"
GOPROXY=""
GORACE=""
GOROOT="$HOME/sdk/go1.11rc1"
GOTMPDIR=""
GOTOOLDIR="/Users/moquality/sdk/go1.11rc1/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/var/folders/6b/nk1h2bp93yn4_c35zvn2845c0000gq/T/tmp.kodrU4ryxD/node/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 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/6b/nk1h2bp93yn4_c35zvn2845c0000gq/T/go-build046724770=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

mkdir example
cd example
go mod init modname
echo 'package main; func main() {println("This is an example.")}' > example.go
go build -v # This produces a file called 'modname'.
go clean -x # This attempts to delete a file called 'example'.

What did you expect to see?

go clean should use the module name to delete rather than the directory name.

What did you see instead?

go clean attempted to use the directory name to delete the previously created executable.

[andybons]

@rsc @bcmills @ianlancetaylor

[bcmills]

Likely the same root cause as #27283.

[rsc]

Possibly same root cause but possibly not. In any event I agree it should use the final (non-version) element of the module path.