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cmd/vet: noCopy is not detected on append #71929

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mneverov opened this issue Feb 24, 2025 · 2 comments
Closed

cmd/vet: noCopy is not detected on append #71929

mneverov opened this issue Feb 24, 2025 · 2 comments
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BugReport Issues describing a possible bug in the Go implementation.

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@mneverov
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Go version

go version go1.24.0 linux/amd64

Output of go env in your module/workspace:

AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/mneverov/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/mneverov/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/home/mneverov/tmp/go-build1453477970=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/mneverov/go/src/github.com/mneverov/test/go.mod'
GOMODCACHE='/home/mneverov/go/pkg/mod'
GOOS='linux'
GOPATH='/home/mneverov/go'
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='on'
GOTELEMETRYDIR='/home/mneverov/.config/go/telemetry'
GOTMPDIR='/home/mneverov/tmp'
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.0'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

func main() {
	s := make([]sync.Mutex, 1, 1)
	s[0] = sync.Mutex{}

	var s1 []sync.Mutex
	for range 1 {
		s1 = append(s, sync.Mutex{})
	}

	s[0].Lock()
	s1[0].Lock()
	fmt.Println("not ok")
}

link.

go vet does not complain about copying the slice during append. Same when a map grows.

What did you see happen?

go vet does not complain about mutexes being copied

What did you expect to see?

call of append copies lock value: sync.Mutex
@seankhliao
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This can't be accurate accurate enough for vet: it's safe to use if the capacity is enough for append without growing the backing array.

@seankhliao seankhliao closed this as not planned Won't fix, can't repro, duplicate, stale Feb 24, 2025
@gabyhelp
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(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)

@gabyhelp gabyhelp added the BugReport Issues describing a possible bug in the Go implementation. label Feb 24, 2025
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@mneverov @seankhliao @gabyhelp