cmd/compile: crash instantiating with recursive type

[jhbrown94]

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

go version go1.18beta1 darwin/amd64

Does this issue reproduce with the latest release?

Yes.

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

Can reproduce in playground, but locally

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/jhbrown/Library/Caches/go-build"
GOENV="/Users/jhbrown/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/jhbrown/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/jhbrown/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/jhbrown/sdk/go1.18beta1"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/jhbrown/sdk/go1.18beta1/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.18beta1"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/d6/kh18314s5wj315ls2klq51nr0000gn/T/go-build1923624470=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I referred to a recursive type from another file, causing a recursive type error to turn into a compiler crash.
See https://go.dev/play/p/FMJLSwjhEMU?v=gotip

What did you expect to see?

Either a clean compile, or a clear warning that I'm breaking the type rules.

What did you see instead?

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x50 pc=0x5c5918]

goroutine 1 [running]:
cmd/compile/internal/ir.TypeNodeAt({0x45e000?, 0xc0?}, 0xe8e630?)
	/usr/local/go/src/cmd/compile/internal/ir/type.go:314 +0x18
...

[ianlancetaylor]

CC @randall77 @danscales @griesemer @findleyr

This is invalid code so not marking as a release blocker.

It may be a bug that this is getting past the type checker.

Here is a single file reproducer.

package foo

var v Box[Step]
type Box[T any] struct{}
type Step = Box[StepBox]
type StepBox Box[Step]

Running go build foo.go gives me

# command-line-arguments
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x50 pc=0x5c5918]

goroutine 1 [running]:
cmd/compile/internal/ir.TypeNodeAt({0x152240?, 0xc0?}, 0xe8e630?)
	/home/iant/go/src/cmd/compile/internal/ir/type.go:314 +0x18
cmd/compile/internal/ir.TypeNode(...)
	/home/iant/go/src/cmd/compile/internal/ir/type.go:303
cmd/compile/internal/noder.(*irgen).expr(0xc000152240, {0xe8f868?, 0xc0003dafc0?})
	/home/iant/go/src/cmd/compile/internal/noder/expr.go:46 +0x945
cmd/compile/internal/noder.(*irgen).typeExpr(0xc000152240, {0xe8f868?, 0xc0003dafc0})
	/home/iant/go/src/cmd/compile/internal/noder/expr.go:409 +0x31
cmd/compile/internal/noder.(*irgen).typeDecl(0xc000152240, 0xc0001520f0, 0xc00007bc20)
	/home/iant/go/src/cmd/compile/internal/noder/decl.go:215 +0x1ab
cmd/compile/internal/noder.(*irgen).generate(0xc000152240, {0xc00000e448, 0x1, 0x203000?})
	/home/iant/go/src/cmd/compile/internal/noder/irgen.go:260 +0x845
cmd/compile/internal/noder.check2({0xc00000e448, 0x1, 0x1})
	/home/iant/go/src/cmd/compile/internal/noder/irgen.go:92 +0x16d
cmd/compile/internal/noder.LoadPackage({0xc00001e1f0, 0x1, 0x0?})
	/home/iant/go/src/cmd/compile/internal/noder/noder.go:90 +0x335
cmd/compile/internal/gc.Main(0xd4bb90)
	/home/iant/go/src/cmd/compile/internal/gc/main.go:191 +0xb13
main.main()
	/home/iant/go/src/cmd/compile/main.go:55 +0xdd

[griesemer]

Yes, I think this should not get past the type checker.

[gopherbot]

Change https://golang.org/cl/379916 mentions this issue: cmd/compile/internal/types2: report an error when using a broken alias

[gopherbot]

Change https://golang.org/cl/380056 mentions this issue: cmd/compile/internal/types2: reorder object processing to avoid broken aliases