cmd/compile: internal compiler error: typecheckclosure: var fn does not have decldepth assigned

[xlab]

What version of Go are you using?

$ go version
go version go1.7.1 darwin/amd64
$ go version
go version go1.7.3 darwin/amd64

What operating system and processor architecture are you using?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/xlab/Documents/dev/go"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/dr/2vrbtj0j7kl1yy32kp5cpn040000gn/T/go-build908632565=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"

What did you do?

The following code fails to compile:

package main

type Foo func(b Bar)

func Bar(fn Foo) {
    func() {
        fn(nil)
    }()
}

https://play.golang.org/p/_5BweYoX9p

What did you expect to see?

A compiler error, describing the case.

What did you see instead?

A panic stacktrace from the compiler, the compilation aborts.

$ go run a.go
# command-line-arguments
./a.go:3: Bar is not a type
./a.go:6: internal compiler error: typecheckclosure: var fn does not have decldepth assigned

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
    /usr/local/go/src/runtime/debug/stack.go:24 +0x79
cmd/compile/internal/gc.Fatalf(0x50d877, 0x39, 0xc42042bb40, 0x1, 0x1)
    /usr/local/go/src/cmd/compile/internal/gc/subr.go:165 +0x248
cmd/compile/internal/gc.typecheckclosure(0xc42041c750, 0xe)
    /usr/local/go/src/cmd/compile/internal/gc/closure.go:113 +0x476
cmd/compile/internal/gc.typecheck1(0xc42041c750, 0xe, 0xc42041c510)
    /usr/local/go/src/cmd/compile/internal/gc/typecheck.go:1895 +0x582d
cmd/compile/internal/gc.typecheck(0xc42041c750, 0xe, 0x0)
    /usr/local/go/src/cmd/compile/internal/gc/typecheck.go:188 +0x654
cmd/compile/internal/gc.typecheck1(0xc42041c990, 0x1, 0x8)
    /usr/local/go/src/cmd/compile/internal/gc/typecheck.go:1200 +0x3cb4
cmd/compile/internal/gc.typecheck(0xc42041c990, 0x1, 0x0)
    /usr/local/go/src/cmd/compile/internal/gc/typecheck.go:188 +0x654
cmd/compile/internal/gc.typecheckslice(0xc420030798, 0x1, 0x1, 0x1)
    /usr/local/go/src/cmd/compile/internal/gc/typecheck.go:49 +0x57
cmd/compile/internal/gc.Main()
    /usr/local/go/src/cmd/compile/internal/gc/main.go:389 +0x178d
cmd/compile/internal/amd64.Main()
    /usr/local/go/src/cmd/compile/internal/amd64/galign.go:93 +0x2fa
main.main()
    /usr/local/go/src/cmd/compile/main.go:33 +0x2a3

[josharian]

cc @mdempsky

[gopherbot]

CL https://golang.org/cl/32415 mentions this issue.

[JayNakrani]

Name.Decldepth is 0 in typecheckclosure(), because in case of Func.Nname.Type==nil, [typecheckfunc() returns](https://github.com/golang/go/blob/master/src/cmd/compile/internal/gc/typecheck.go#L3421&q="if t == nil {") without [initializing the Decldepth](https://github.com/golang/go/blob/master/src/cmd/compile/internal/gc/typecheck.go#L3432&q="ln.Name.Decldepth = 1") for func's autodcls.

After golang.org/cl/32415:

$ ../pkg/tool/linux_amd64/compile ../test/fixedbugs/issue17588.go 
../test/fixedbugs/issue17588.go:9: Hehe is not a type