cmd/compile: compiler panic with generics across packages and pointer type parameter

[JOT85]

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

$ go version
go version go1.18rc1 linux/amd64

Does this issue reproduce with the latest release?

Yes

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/jp/.cache/go-build"
GOENV="/home/jp/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/jp/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/jp/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/jp/sdk/go1.18rc1"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/jp/sdk/go1.18rc1/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.18rc1"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/jp/sites/ian-turner-store/broken/go.mod"
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 -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3364662887=/tmp/go-build -gno-record-gcc-switches"

What did you do?

go.mod

module go.jot.me.uk/broken

go 1.18

main.go

package main

import (
	"go.jot.me.uk/broken/foo"
)

func main() {
    foo.DoSomething[byte]()
}

foo/foo.go

package foo

type A[T any] struct{}

func (_ A[T]) Method() {}

func DoSomething[P any]() {
    a := A[*byte]{}
    a.Method()
}

What did you expect to see?

The program compile.

What did you see instead?

$ go build .
# go.jot.me.uk/broken
./main.go:8:26: internal compiler error: panic: runtime error: invalid memory address or nil pointer dereference

Please file a bug report including a short program that triggers the error.
https://go.dev/issue/new

[ianlancetaylor]

This builds with GOEXPERIMENT=unified.

CC @danscales @randall77 @griesemer @findleyr

Compiler backtrace:

# t
./main.go:8:26: internal compiler error: panic: runtime error: invalid memory address or nil pointer dereference

goroutine 1 [running]:
runtime/debug.Stack()
	/home/iant/go/src/runtime/debug/stack.go:24 +0x65
cmd/compile/internal/base.FatalfAt({0x21524758?, 0x7f7b?}, {0xd22309, 0x9}, {0xc000120fd0, 0x1, 0x1})
	/home/iant/go/src/cmd/compile/internal/base/print.go:227 +0x1d7
cmd/compile/internal/base.Fatalf(...)
	/home/iant/go/src/cmd/compile/internal/base/print.go:196
cmd/compile/internal/gc.handlePanic()
	/home/iant/go/src/cmd/compile/internal/gc/main.go:49 +0x85
panic({0xcabae0, 0x1310df0})
	/home/iant/go/src/runtime/panic.go:838 +0x207
cmd/compile/internal/types.(*Type).Bound(0x0?)
	/home/iant/go/src/cmd/compile/internal/types/type.go:1900 +0x18
cmd/compile/internal/typecheck.Shapify(0x40d365?, 0xbf3453?, 0xbf3453?)
	/home/iant/go/src/cmd/compile/internal/typecheck/subr.go:1453 +0xbf
cmd/compile/internal/noder.(*genInst).getInstantiation(0x1399e20, 0xc00041b520, {0xc00000e690, 0x1, 0xc0004114a0?}, 0x1)
	/home/iant/go/src/cmd/compile/internal/noder/stencil.go:665 +0x2d0
cmd/compile/internal/noder.(*genInst).scanForGenCalls.func1({0xe98dd8, 0xc000179290?})
	/home/iant/go/src/cmd/compile/internal/noder/stencil.go:151 +0x2df
cmd/compile/internal/ir.Visit.func1({0xe98dd8, 0xc000179290})
	/home/iant/go/src/cmd/compile/internal/ir/visit.go:105 +0x30
cmd/compile/internal/ir.doNodes(...)
	/home/iant/go/src/cmd/compile/internal/ir/node_gen.go:1512
cmd/compile/internal/ir.(*Func).doChildren(0xe99738?, 0xc00000ddb8?)
	/home/iant/go/src/cmd/compile/internal/ir/func.go:156 +0x6e
cmd/compile/internal/ir.DoChildren(...)
	/home/iant/go/src/cmd/compile/internal/ir/visit.go:94
cmd/compile/internal/ir.Visit.func1({0xe99738, 0xc0004114a0})
	/home/iant/go/src/cmd/compile/internal/ir/visit.go:106 +0x57
cmd/compile/internal/ir.Visit({0xe99738, 0xc0004114a0}, 0xc000035f00)
	/home/iant/go/src/cmd/compile/internal/ir/visit.go:108 +0xb8
cmd/compile/internal/noder.(*genInst).scanForGenCalls(0x1399e20, {0xe99738, 0xc0004114a0})
	/home/iant/go/src/cmd/compile/internal/noder/stencil.go:133 +0x1f0
cmd/compile/internal/noder.(*genInst).buildInstantiations(0x1399e20)
	/home/iant/go/src/cmd/compile/internal/noder/stencil.go:67 +0xc5
cmd/compile/internal/noder.BuildInstantiations(...)
	/home/iant/go/src/cmd/compile/internal/noder/stencil.go:44
cmd/compile/internal/noder.(*irgen).generate(0xc000154300, {0xc00000e448, 0x1, 0x203000?})
	/home/iant/go/src/cmd/compile/internal/noder/irgen.go:331 +0x3d1
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({0xc00001e220, 0x1, 0x0?})
	/home/iant/go/src/cmd/compile/internal/noder/noder.go:90 +0x335
cmd/compile/internal/gc.Main(0xd52510)
	/home/iant/go/src/cmd/compile/internal/gc/main.go:191 +0xb13
main.main()
	/home/iant/go/src/cmd/compile/main.go:55 +0xdd

[findleyr]

Playground link:
https://go.dev/play/p/3YuX_i5W00s?v=gotip

Marking as a release blocker as this is a valid program that does not compile.

[JOT85]

Playground link:
https://go.dev/play/p/3YuX_i5W00s?v=gotip

Thanks! I didn't realise you could include multiple files in the playground, neat :)

[danscales]

Missing nil check in some code related to structural type params. I'll fix this.

[gopherbot]

Change https://go.dev/cl/388116 mentions this issue: cmd/compile: add missing nil check for tparam in Shapify