cmd/compile: internal compiler error: impure type set used in value type

[kckrinke]

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

$ go version
go version go1.20.1 linux/arm64

Does this issue reproduce with the latest release?

Yes. Confirmed with v1.20.4.

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

go env Output

$ go env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/quo/local/enjenv/golang/cache"
GOENV="/quo/local/enjenv/golang/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS="-modcacherw"
GOHOSTARCH="arm64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/quo/local/enjenv/golang/modcache"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/quo"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/quo/local/enjenv/golang/go"
GOSUMDB="sum.golang.org"
GOTMPDIR="/quo/local/enjenv/golang/tmp"
GOTOOLDIR="/quo/local/enjenv/golang/go/pkg/tool/linux_arm64"
GOVCS=""
GOVERSION="go1.20.4"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/quo/src/poc/go-impure-value/go.mod"
GOWORK=""
CGO_CFLAGS="-O2 -g"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-O2 -g"
CGO_FFLAGS="-O2 -g"
CGO_LDFLAGS="-O2 -g"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/quo/local/enjenv/golang/tmp/go-build2070028500=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Just experimenting with using generics to solve some design pattern conveniences and discovered that I apparently need to file this bug report, so that's what this bug report is about.

Here's a short program demonstrating the problem case.

What did you expect to see?

Dunno exactly, still wrapping my brain around the generics thing and this was simply exploration through experimentation. The short program was extracted from the work I'm doing on a much larger project, which means I must be confused about the rules of generics and need to scale things back a bit.

What did you see instead?

$ cat main.go
package main

import (
	"fmt"
)

type Number interface {
	uint64 | int64 | float64
}

type Variable interface {
	Number | []interface{} | interface{}
}

func main() {
	fmt.Printf("Hello World\n")
}
$ go build -v
go-impure-value
# go-impure-value
./main.go:7:6: internal compiler error: impure type set used in value type

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

[seankhliao]

cc @golang/compiler

tip comes with a stacktrace:

go build 
# go.seankhliao.com/testrepo0189
go.seankhliao.com/testrepo0189/main.go:7:6: internal compiler error: impure type set used in value type

goroutine 1 [running]:
runtime/debug.Stack()
	../../sdk/gotip/src/runtime/debug/stack.go:24 +0x5e
cmd/compile/internal/base.FatalfAt({0x4619e0?, 0xc0?}, {0xd089ce, 0x22}, {0x0, 0x0, 0x0})
	../../sdk/gotip/src/cmd/compile/internal/base/print.go:234 +0x1d7
cmd/compile/internal/base.Fatalf(...)
	../../sdk/gotip/src/cmd/compile/internal/base/print.go:203
cmd/compile/internal/noder.(*reader).unionType(0xc0004619e0)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:555 +0x9e
cmd/compile/internal/noder.(*reader).doTyp(0xc0004619e0)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:527 +0x1df
cmd/compile/internal/noder.(*pkgReader).typIdx(0xc0004442a0, {0x44e249?, 0x0?}, 0xc00047c0d0, 0x1)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:430 +0x18a
cmd/compile/internal/noder.(*reader).typWrapped(0xc000461d50, 0x1?)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:389 +0x3a
cmd/compile/internal/noder.(*reader).typ(...)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:383
cmd/compile/internal/noder.(*reader).interfaceType(0xc000461d50)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:576 +0x1ed
cmd/compile/internal/noder.(*reader).doTyp(0xc000461d50)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:525 +0x1cf
cmd/compile/internal/noder.(*pkgReader).typIdx(0xc0004442a0, {0x461ef8?, 0xc0?}, 0xc00047c0d0, 0x0)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:430 +0x18a
cmd/compile/internal/noder.(*reader).typWrapped(0xc000192480, 0xd0?)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:389 +0x3a
cmd/compile/internal/noder.(*pkgReader).objIdx(0xc0004442a0, 0x0, {0x0?, 0x0, 0x0}, {0x13b1b80?, 0x0, 0x0}, 0xe7?)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:783 +0x6e5
cmd/compile/internal/noder.(*pkgReader).objInstIdx(0xc0004625a0?, {0x4442a0?, {0x13b1b80?, 0xb064e5?, 0x1?}}, 0xc00047c000, 0xa0?)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:672 +0x87
cmd/compile/internal/noder.(*reader).obj(0xc0004625a0)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:644 +0x46
cmd/compile/internal/noder.(*reader).doTyp(0xc0004625a0)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:501 +0x6d
cmd/compile/internal/noder.(*pkgReader).typIdx(0xc0004442a0, {0x4628e0?, 0xc0?}, 0xc00047c000, 0x1)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:430 +0x18a
cmd/compile/internal/noder.(*reader).typWrapped(0xc0004628e0, 0x78?)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:389 +0x3a
cmd/compile/internal/noder.(*reader).typ(...)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:383
cmd/compile/internal/noder.(*reader).unionType(0xc0004628e0)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:549 +0x59
cmd/compile/internal/noder.(*reader).doTyp(0xc0004628e0)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:527 +0x1df
cmd/compile/internal/noder.(*pkgReader).typIdx(0xc0004442a0, {0x44e249?, 0x0?}, 0xc00047c000, 0x1)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:430 +0x18a
cmd/compile/internal/noder.(*reader).typWrapped(0xc000462c50, 0x1?)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:389 +0x3a
cmd/compile/internal/noder.(*reader).typ(...)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:383
cmd/compile/internal/noder.(*reader).interfaceType(0xc000462c50)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:576 +0x1ed
cmd/compile/internal/noder.(*reader).doTyp(0xc000462c50)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:525 +0x1cf
cmd/compile/internal/noder.(*pkgReader).typIdx(0xc0004442a0, {0x462df8?, 0xc0?}, 0xc00047c000, 0x0)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:430 +0x18a
cmd/compile/internal/noder.(*reader).typWrapped(0xc000192300, 0x20?)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:389 +0x3a
cmd/compile/internal/noder.(*pkgReader).objIdx(0xc0004442a0, 0x1, {0x0?, 0x0, 0x0}, {0x13b1b80?, 0x0, 0x0}, 0x0?)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:783 +0x6e5
cmd/compile/internal/noder.(*pkgReader).objInstIdx(0xc000463748?, {0x0?, {0x13b1b80?, 0x44e249?, 0x8?}}, 0x0, 0x1?)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:672 +0x87
cmd/compile/internal/noder.(*reader).obj(0xc000463748)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:644 +0x46
cmd/compile/internal/noder.(*reader).pkgObjs(0xc000463748, 0xc00018a0c0)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:3373 +0x9b
cmd/compile/internal/noder.(*reader).pkgDecls(0xc000463748, 0xc00018a0c0)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:3362 +0x1af
cmd/compile/internal/noder.(*reader).pkgInit(0xc000463748, 0xc00047a630?, 0xc00018a0c0)
	../../sdk/gotip/src/cmd/compile/internal/noder/reader.go:3301 +0xd6
cmd/compile/internal/noder.unified({0x0?, {0x0?, 0x0?}}, {0xc000134468?, 0xc3d860?, 0x6bbd36895316fcd?})
	../../sdk/gotip/src/cmd/compile/internal/noder/unified.go:92 +0x2cf
cmd/compile/internal/noder.LoadPackage({0xc000142100, 0x1, 0x2})
	../../sdk/gotip/src/cmd/compile/internal/noder/noder.go:77 +0x450
cmd/compile/internal/gc.Main(0xd24190)
	../../sdk/gotip/src/cmd/compile/internal/gc/main.go:198 +0xc17
main.main()
	../../sdk/gotip/src/cmd/compile/main.go:57 +0xf9

[mdempsky]

Thanks for the report. Your code is valid and should work. I'm sorry that it doesn't.

This is a little nuanced, but the issue here is that your defined type Variable is a "pure" interface, but it embeds a non-pure interface (Number). This should be allowed, but hits an unexpected code path today.

You can workaround this by simplifying Number | []any | any to just any, or removing that line altogether.

[kckrinke]

You're welcome! Nice to know I was on track. That's basically what I ended up doing. thanks for the notes!

[gopherbot]

Change https://go.dev/cl/495455 mentions this issue: cmd/compile/internal/noder: suppress unionType consistency check