internal: slice initialization with colons should throw syntax error

[fumin]

Go version

go version go1.23.2 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/shaoyu/.cache/go-build'
GOENV='/home/shaoyu/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/shaoyu/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/shaoyu/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.23.2'
GODEBUG=''
GOTELEMETRY='on'
GOTELEMETRYDIR='/home/shaoyu/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/shaoyu/a/qising/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 -ffile-prefix-map=/tmp/go-build3719528684=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I ran the following program, while intentionally mistyped a comma with a colon in slice initialization:

https://go.dev/play/p/uZWlwJV9cxI

package main

import "fmt"

func main() {
	// Correct syntax.
	a := []int{1, 3}

	// Wrong syntax, a bug!
	b := []int{1: 3}

	fmt.Println("a", a)
	fmt.Println("b", b)
}

What did you see happen?

The program prints:

a [1 3]
b [0 3]

No idea why the contents of b is as such.

What did you expect to see?

Since b is initialized not with a comma, the compiler should throw an syntax error.

[gabyhelp]

Related Issues

• spec: poorly documented slice definition syntax #30625 (closed)
• Some inconsistent Values on Slice output #34428 (closed)
• Slice: why extra element can be access by [:], but cannot with [] #29473 (closed)

Related Discussions

• Strange syntax inconsistency

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[fumin]

Duplicate of #30625 , closing.