cmd/compile: internal compiler error: unexpected dot in identifier: .anon0

[mhilton]

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

go version devel +736390c2bd Thu Apr 26 07:07:18 2018 +0000 linux/amd64

Does this issue reproduce with the latest release?

No, version 1.10.1 seems fine

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

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/mhilton/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/mhilton/go"
GORACE=""
GOROOT="/home/mhilton/opt/go"
GOTMPDIR=""
GOTOOLDIR="/home/mhilton/opt/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build736391734=/tmp/go-build -gno-record-gcc-switches"

What did you do?

1. Create the following files:

==> local/a/a.go <==

package a

import "local/a/b"

var (
	x b.X
	y = x.Y
)

==> local/a/b/b.go <==

package b

type X interface {
	Y(int)
}

==> local/a/a_test.go <==

package a

var Y = &y

run go test local/a

What did you expect to see?

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x4e5e2d]

goroutine 1 [running]:
local/a.init()
	/home/mhilton/go/src/local/a/a.go:7 +0x4d
FAIL	local/a	0.003s

What did you see instead?

# local/a [local/a.test]
<autogenerated>:1: internal compiler error: unexpected dot in identifier: .anon0

goroutine 1 [running]:
runtime/debug.Stack(0x0, 0x0, 0x0)
	/home/mhilton/opt/go/src/runtime/debug/stack.go:24 +0xa7
cmd/compile/internal/gc.Fatalf(0xc13281, 0x20, 0xc0003a2fb0, 0x1, 0x1)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/subr.go:182 +0x1f7
cmd/compile/internal/gc.(*exportWriter).localIdent(0xc00034acf0, 0xc00006f500, 0x0)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:1383 +0x3e1
cmd/compile/internal/gc.(*exportWriter).param(0xc00034acf0, 0xc000022480)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:723 +0x92
cmd/compile/internal/gc.(*exportWriter).paramList(0xc00034acf0, 0xc00000c0e8, 0x1, 0x1)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:717 +0x5a
cmd/compile/internal/gc.(*exportWriter).signature(0xc00034acf0, 0xc00006f560)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:707 +0x4b
cmd/compile/internal/gc.(*exportWriter).doTyp(0xc00034acf0, 0xc00006f560)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:646 +0x6f0
cmd/compile/internal/gc.(*iexporter).typOff(0xc0000a4ea0, 0xc00006f560, 0x1200000000000001)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:597 +0xab
cmd/compile/internal/gc.(*exportWriter).typ(0xc00034ac60, 0xc00006f560)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:580 +0x38
cmd/compile/internal/gc.(*exportWriter).doTyp(0xc00034ac60, 0xc00006f740)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:622 +0x731
cmd/compile/internal/gc.(*iexporter).typOff(0xc0000a4ea0, 0xc00006f740, 0x7ffcf3c1c5fc)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:597 +0xab
cmd/compile/internal/gc.(*exportWriter).typ(0xc00034abd0, 0xc00006f740)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:580 +0x38
cmd/compile/internal/gc.(*iexporter).doDecl(0xc0000a4ea0, 0xc00038e3c0)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:422 +0x2ef
cmd/compile/internal/gc.iexport(0xc00035f000)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/iexport.go:276 +0x38d
cmd/compile/internal/gc.dumpexport(0xc00008ecc0)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/export.go:79 +0x8f
cmd/compile/internal/gc.dumpCompilerObj(0xc00008ecc0)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/obj.go:119 +0x39
cmd/compile/internal/gc.dumpobj1(0x7ffcf3c1c508, 0x23, 0x3)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/obj.go:70 +0x15b
cmd/compile/internal/gc.dumpobj()
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/obj.go:51 +0x60
cmd/compile/internal/gc.Main(0xc209c8)
	/home/mhilton/opt/go/src/cmd/compile/internal/gc/main.go:684 +0x299a
main.main()
	/home/mhilton/opt/go/src/cmd/compile/main.go:49 +0x96

FAIL	local/a [build failed]

[mvdan]

This seems to be in the code added by @mdempsky for the new indexed export format, so it's probably best if he has a look.

[griesemer]

Simpler. Compiling this package causes the error. The problem is a possibly overly strict check in the exported. The solution may be as simple as exporting ".anonX" named parameters as "".

package p

type T interface {
	M(int)
}

var x T
var M = x.M

[gopherbot]

Change https://golang.org/cl/116376 mentions this issue: cmd/compile: revert internal parameter rename (from ".anonX" to "") before export