affected/package: golang.org/x/exp/slices#Compact

[jesseduffield]

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

1.18

Does this issue reproduce with the latest release?

Yes

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

go env Output

GO111MODULE="auto"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/jesseduffieldduffield/Library/Caches/go-build"
GOENV="/Users/jesseduffieldduffield/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/jesseduffieldduffield/.gvm/pkgsets/go1.18/global/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/jesseduffieldduffield/.gvm/pkgsets/go1.18/global"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/jesseduffieldduffield/.gvm/gos/go1.18"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/jesseduffieldduffield/.gvm/gos/go1.18/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.18"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/jesseduffieldduffield/repos/list/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/d_/3fryg6d934l7jxttrz1z21bh0000gn/T/go-build1796431560=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

https://go.dev/play/p/AP_5oYMfmUh

package main

import (
	"fmt"

	"golang.org/x/exp/slices"
)

func main() {
	slice := []int{1, 1, 2}
	output := slices.Compact(slice)
	fmt.Printf("%v\n", output) // outputs [1 2] (expected)
	fmt.Printf("%v\n", slice)  // outputs [1 2 2] (not expected)
}

What did you expect to see?

Expected both the resultant slice and the output slice to be [1 2]

What did you see instead?

Resultant slice is [1 2 2]

If this is expected behaviour, it would be good to specify in the docs that the original slice should not be used after calling this function and that instead you should only use the output slice.

[seankhliao]

I believe it already does:

Compact modifies the contents of the slice s; it does not create a new slice.