cmd/compile: unused variable is not caught if it's assigned in a function closure

[songgao]

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

go version go1.6.2 linux/amd64

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

GOARCH="amd64"
GOBIN="/home/songgao/gopath/bin"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/songgao/gopath"
GORACE=""
GOROOT="/usr/lib/go"
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GO15VENDOREXPERIMENT="1"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"
CXX="g++"
CGO_ENABLED="1"

1. What did you do?

songgao at Song-ThinkPad in /tmp 
$ cat main.go
package main

func main() {
    var a int
    a = 2
}

songgao at Song-ThinkPad in /tmp 
$ go run main.go
# command-line-arguments
./main.go:4: a declared and not used

songgao at Song-ThinkPad in /tmp 
$ vim main.go

songgao at Song-ThinkPad in /tmp 
$ cat main.go
package main

func main() {
    var a int
    func() {
        a = 2
    }()
}

songgao at Song-ThinkPad in /tmp 
$ go run main.go

songgao at Song-ThinkPad in /tmp 
$ echo $?
0

1. What did you expect to see?

The declared but unused variable gets caught even if it's assigned in a function closure.

1. What did you see instead?

Not caught.

P.S. Interestingly, the same error was successfully caught by :GoRename command (which uses gorename) in vim.

[bradfitz]

Technically this isn't a violation of the spec, which only says:

Implementation restriction: A compiler may make it illegal to declare a variable inside a function body if the variable is never used.

But I agree it'd be nice if our various tools had consistent behavior.

[griesemer]

Duplicate of #3059.

[griesemer]

gorename uses go/types which correctly (in my mind) reports this as an error.