cmd/compile: inconsistent errors for init expr mismatches for vars and consts

[ProCode-Software]

Go version

go version go1.26.4 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/procode/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/procode/.config/go/env'
GOEXE=''
GOEXPERIMENT='jsonv2'
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build277106179=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/procode/Development/klar/go.mod'
GOMODCACHE='/home/procode/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/procode/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='off'
GOTELEMETRYDIR='/home/procode/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.26.4'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

Playground link: https://go.dev/play/p/GXOXP7yDZG__0

var x, y = 1

const a, b = 2

What did you see happen?

./prog.go:5:12: assignment mismatch: 2 variables but 1 value
./prog.go:7:10: missing init expr for b

What did you expect to see?

Consistent error messages when variables and constants have mismatched init expression counts

[gabyhelp]

Related Issues

• cmd/compile: inconsistent error message for assignment mismatch #30085 (closed)
• cmd/compile: clearer error for invalid const values #69955 (closed)
• cmd/compile: = and := errors are unnecessarily different #48558 (closed)
• using consts in the same line #39266 (closed)
• cmd/gc: Better wording on constant declaration #6557 (closed)
• go/types: provide better error message for errors in n:1 init assignment #15783

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

[dmitshur]

CC @golang/compiler.

[griesemer]

Variable assignments and constant declarations are not the same thing, so it's not clear that "consistency" is what we need here. Specifically, we don't have an "assignment" with constant declarations. In both cases the error messages are pretty clear even if they follow a different pattern.

Leaving open in case we decide that we can/should do something here.