cmd/compile: internal compiler error: assertion failed with type aliases

[cachesdev]

Go version

go version go1.24.2 linux/amd64

Output of go env in your module/workspace:

AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/caches/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/caches/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build918672315=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/caches/repos/veritas/go.mod'
GOMODCACHE='/home/caches/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/caches/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/caches/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.2'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

playground link

What did you see happen?

running or trying to build this code causes the following error:

./prog.go:43:6: internal compiler error: assertion failed

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

Go build failed.

if importing the code as a package, we see the following error from gopls (package name redacted):

could not import github.com/(...)/validator (missing import github.com/(...)/validator)compilerBrokenImport

removing the type aliases makes the code runnable.
playground link with type aliases removed

What did you expect to see?

a passing test. valid printed in the console.

[cachesdev]

at some point I also managed to trigger a panic, but I cannot reproduce it anymore. it may have been in an older go version. I did conserve the output:

❯ go test ./...
# github.com/(...)/validator_test [github.com/(...)/validator.test]
fatal error: all goroutines are asleep - deadlock!

goroutine 1 [sync.Mutex.Lock]:
internal/sync.runtime_SemacquireMutex(0x7f30e6065108?, 0xd3?, 0xc000470c88?)
	runtime/sema.go:95 +0x25
internal/sync.(*Mutex).lockSlow(0xc00046c6b8)
	internal/sync/mutex.go:149 +0x15d
internal/sync.(*Mutex).Lock(...)
	internal/sync/mutex.go:70
sync.(*Mutex).Lock(...)
	sync/mutex.go:46
cmd/compile/internal/types2.(*Named).resolve(0xc00046c690)
	cmd/compile/internal/types2/named.go:176 +0x5f
cmd/compile/internal/types2.(*Named).TypeParams(...)
	cmd/compile/internal/types2/named.go:322
cmd/compile/internal/types2.(*subster).typ(0xc0004713c8, {0x102cce8, 0xc00046c700})
	cmd/compile/internal/types2/subst.go:245 +0x82b
cmd/compile/internal/types2.(*subster).var_(0xc000471208?, 0xc00046c770)
	cmd/compile/internal/types2/subst.go:288 +0x2c
cmd/compile/internal/types2.substList[...](...)
	cmd/compile/internal/types2/subst.go:317
cmd/compile/internal/types2.(*subster).tuple(0x0?, 0xc000406528)
	cmd/compile/internal/types2/subst.go:304 +0xa3
cmd/compile/internal/types2.(*subster).typ(0xc0004713c8, {0x102ccc0, 0xc000465280})
	cmd/compile/internal/types2/subst.go:164 +0x44a
cmd/compile/internal/types2.(*Checker).subst(0x0, {0x0?, 0x0?, 0x0?}, {0x102ccc0, 0xc000465280}, 0xc0004668d0, 0x0, 0xc000113400)
	cmd/compile/internal/types2/subst.go:78 +0x1ac
cmd/compile/internal/types2.(*Checker).newAliasInstance(0x0, {0x0?, 0xe5e04491?, 0x7f30?}, 0xc0004652c0, {0xc000039b50, 0x1, 0x1}, 0x0, 0xc000113400)
	cmd/compile/internal/types2/alias.go:165 +0x1c5
cmd/compile/internal/types2.(*Checker).instance(0x0, {0x0, 0x0, 0x0}, {0x102e3d8, 0xc0004652c0}, {0xc000039b50, 0x1, 0x1}, 0x0, ...)
	cmd/compile/internal/types2/instantiate.go:150 +0x4b0
cmd/compile/internal/types2.Instantiate(0xc000113400, {0x102cd10, 0xc0004652c0}, {0xc000039b50, 0x1, 0x1}, 0x0)
	cmd/compile/internal/types2/instantiate.go:70 +0x326
cmd/compile/internal/importer.(*reader).doTyp(0xc000471800)
	cmd/compile/internal/importer/ureader.go:258 +0xcc
cmd/compile/internal/importer.(*pkgReader).typIdx(0xc000000540, {0x540?, 0xc0?}, 0xc00045cde0)
	cmd/compile/internal/importer/ureader.go:231 +0x18e
cmd/compile/internal/importer.(*reader).typ(0xc000471a28)
	cmd/compile/internal/importer/ureader.go:201 +0x68
cmd/compile/internal/importer.(*reader).doTyp(0xc000471a28)
	cmd/compile/internal/importer/ureader.go:279 +0x15b
cmd/compile/internal/importer.(*pkgReader).typIdx(0xc000000540, {0x540?, 0xc0?}, 0xc00045cde0)
	cmd/compile/internal/importer/ureader.go:231 +0x18e
cmd/compile/internal/importer.(*reader).typ(0xc000471d20)
	cmd/compile/internal/importer/ureader.go:201 +0x68
cmd/compile/internal/importer.(*reader).structType(0xc000471d20)
	cmd/compile/internal/importer/ureader.go:295 +0xe7
cmd/compile/internal/importer.(*reader).doTyp(0xc000471d20)
	cmd/compile/internal/importer/ureader.go:281 +0x3a5
cmd/compile/internal/importer.(*pkgReader).typIdx(0xc000000540, {0x45c300?, 0xc0?}, 0xc00045cde0)
	cmd/compile/internal/importer/ureader.go:231 +0x18e
cmd/compile/internal/importer.(*reader).typ(0xc00045ce40)
	cmd/compile/internal/importer/ureader.go:201 +0x68
cmd/compile/internal/importer.ReadPackage.(*pkgReader).objIdx.func1.1(0x32?)
	cmd/compile/internal/importer/ureader.go:450 +0x3e
cmd/compile/internal/types2.(*Named).resolve(0xc00046c690)
	cmd/compile/internal/types2/named.go:215 +0xf7
cmd/compile/internal/types2.(*Named).TypeParams(...)
	cmd/compile/internal/types2/named.go:322
cmd/compile/internal/types2.(*subster).typ(0xc000472608, {0x102cce8, 0xc00046c700})
	cmd/compile/internal/types2/subst.go:245 +0x82b
cmd/compile/internal/types2.(*subster).var_(0xc000472448?, 0xc00046c770)
	cmd/compile/internal/types2/subst.go:288 +0x2c
cmd/compile/internal/types2.substList[...](...)
	cmd/compile/internal/types2/subst.go:317
cmd/compile/internal/types2.(*subster).tuple(0x7f30e606e170?, 0xc000406528)
	cmd/compile/internal/types2/subst.go:304 +0xa3
cmd/compile/internal/types2.(*subster).typ(0xc000472608, {0x102ccc0, 0xc000465280})
	cmd/compile/internal/types2/subst.go:164 +0x44a
cmd/compile/internal/types2.(*Checker).subst(0x0, {0x0?, 0x0?, 0x0?}, {0x102ccc0, 0xc000465280}, 0xc0004667e0, 0x0, 0xc000113400)
	cmd/compile/internal/types2/subst.go:78 +0x1ac
cmd/compile/internal/types2.(*Checker).newAliasInstance(0x0, {0x0?, 0xe5e04491?, 0x7f30?}, 0xc0004652c0, {0xc000039b20, 0x1, 0x1}, 0x0, 0xc000113400)
	cmd/compile/internal/types2/alias.go:165 +0x1c5
cmd/compile/internal/types2.(*Checker).instance(0x0, {0x0, 0x0, 0x0}, {0x102e3d8, 0xc0004652c0}, {0xc000039b20, 0x1, 0x1}, 0x0, ...)
	cmd/compile/internal/types2/instantiate.go:150 +0x4b0
cmd/compile/internal/types2.Instantiate(0xc000113400, {0x102cd10, 0xc0004652c0}, {0xc000039b20, 0x1, 0x1}, 0x0)
	cmd/compile/internal/types2/instantiate.go:70 +0x326
cmd/compile/internal/importer.(*reader).doTyp(0xc000472a40)
	cmd/compile/internal/importer/ureader.go:258 +0xcc
cmd/compile/internal/importer.(*pkgReader).typIdx(0xc000000540, {0x540?, 0xc0?}, 0xc00045cb40)
	cmd/compile/internal/importer/ureader.go:231 +0x18e
cmd/compile/internal/importer.(*reader).typ(0xc0000a6c68)
	cmd/compile/internal/importer/ureader.go:201 +0x68
cmd/compile/internal/importer.(*reader).doTyp(0xc0000a6c68)
	cmd/compile/internal/importer/ureader.go:279 +0x15b
cmd/compile/internal/importer.(*pkgReader).typIdx(0xc000000540, {0x540?, 0xc0?}, 0xc00045cb40)
	cmd/compile/internal/importer/ureader.go:231 +0x18e
cmd/compile/internal/importer.(*reader).typ(0xc00045cc00)
	cmd/compile/internal/importer/ureader.go:201 +0x68
cmd/compile/internal/importer.(*reader).param(0xc00045cc00)
	cmd/compile/internal/importer/ureader.go:365 +0x65
cmd/compile/internal/importer.(*reader).params(0xc00045cc00)
	cmd/compile/internal/importer/ureader.go:355 +0x74
cmd/compile/internal/importer.(*reader).signature(0xc00045cc00, 0x0, {0x0, 0x0, 0x0}, {0xc0000788a8, 0x1, 0x1})
	cmd/compile/internal/importer/ureader.go:344 +0x65
cmd/compile/internal/importer.ReadPackage.(*pkgReader).objIdx.func1()
	cmd/compile/internal/importer/ureader.go:437 +0x325
cmd/compile/internal/types2.resolve.func1()
	cmd/compile/internal/types2/scope.go:176 +0x39
sync.(*Once).doSlow(0xc0000a70f8?, 0xc0000a7050?)
	sync/once.go:78 +0xab
sync.(*Once).Do(...)
	sync/once.go:69
cmd/compile/internal/types2.resolve({0xc000010dc7?, 0xeb2c949b29a6f35d?}, {0x1035c60?, 0xc0004661e0?})
	cmd/compile/internal/types2/scope.go:175 +0x77
cmd/compile/internal/types2.(*Scope).Lookup(0xe24840?, {0xc000010dc7, 0x5})
	cmd/compile/internal/types2/scope.go:71 +0x4b
cmd/compile/internal/types2.(*Checker).selector(0xc0000036c0, 0xc000465180, 0xc0004039a0, 0x0, 0x0)
	cmd/compile/internal/types2/call.go:720 +0x21f
cmd/compile/internal/types2.(*Checker).exprInternal(0xc0000036c0, 0xc0000a74a8?, 0xc000465180, {0x1030d18, 0xc0004039a0}, {0x0?, 0x0?})
	cmd/compile/internal/types2/expr.go:1052 +0x6cc
cmd/compile/internal/types2.(*Checker).rawExpr(0xc0000036c0, 0x0, 0xc000465180, {0x1030d18?, 0xc0004039a0?}, {0x0?, 0x0?}, 0x1)
	cmd/compile/internal/types2/expr.go:959 +0x194
cmd/compile/internal/types2.(*Checker).exprOrType(0xc0000036c0, 0xc000465180, {0x1030d18?, 0xc0004039a0?}, 0xe0?)
	cmd/compile/internal/types2/expr.go:1335 +0x45
cmd/compile/internal/types2.(*Checker).callExpr(0xc0000036c0, 0xc000465180, 0xc00013d340)
	cmd/compile/internal/types2/call.go:185 +0x105
cmd/compile/internal/types2.(*Checker).exprInternal(0xc0000036c0, 0x167b400?, 0xc000465180, {0x1030d60, 0xc00013d340}, {0x102cce8?, 0xc00046c460?})
	cmd/compile/internal/types2/expr.go:1104 +0x688
cmd/compile/internal/types2.(*Checker).rawExpr(0xc0000036c0, 0x0, 0xc000465180, {0x1030d60?, 0xc00013d340?}, {0x102cce8?, 0xc00046c460?}, 0x0)
	cmd/compile/internal/types2/expr.go:959 +0x194
cmd/compile/internal/types2.(*Checker).exprWithHint(0xc0000036c0, 0xc000465180, {0x1030d60, 0xc00013d340}, {0x102cce8, 0xc00046c460})
	cmd/compile/internal/types2/expr.go:1325 +0x65
cmd/compile/internal/types2.(*Checker).indexedElts(0xc0000036c0, {0xc0000392b0, 0x1, 0xc0000a7e40?}, {0x102cce8, 0xc00046c460}, 0xffffffffffffffff)
	cmd/compile/internal/types2/literals.go:386 +0x13e
cmd/compile/internal/types2.(*Checker).compositeLit(0xc0000036c0, 0xc000465040, 0xc000044780, {0x0?, 0x0?})
	cmd/compile/internal/types2/literals.go:263 +0x251
cmd/compile/internal/types2.(*Checker).exprInternal(0xc0000036c0, 0x41b9c5?, 0xc000465040, {0x1030e38, 0xc000044780}, {0x0?, 0x0?})
	cmd/compile/internal/types2/expr.go:1040 +0x5a5
cmd/compile/internal/types2.(*Checker).rawExpr(0xc0000036c0, 0x0, 0xc000465040, {0x1030e38?, 0xc000044780?}, {0x0?, 0x0?}, 0x0)
	cmd/compile/internal/types2/expr.go:959 +0x194
cmd/compile/internal/types2.(*Checker).expr(0xc0000036c0, 0x0?, 0xc000465040, {0x1030e38?, 0xc000044780?})
	cmd/compile/internal/types2/expr.go:1275 +0x30
cmd/compile/internal/types2.(*Checker).initVars(0xc0000036c0, {0xc000078888, 0x1, 0x1?}, {0xc0004748a8, 0xffffffffffffffff?, 0x7f30e6065108?}, {0x0, 0x0})
	cmd/compile/internal/types2/assignments.go:409 +0x645
cmd/compile/internal/types2.(*Checker).shortVarDecl(...)
	cmd/compile/internal/types2/assignments.go:584
cmd/compile/internal/types2.(*Checker).stmt(0xc0000036c0, 0x0, {0x102ea90, 0xc000405240})
	cmd/compile/internal/types2/stmt.go:508 +0x385c
cmd/compile/internal/types2.(*Checker).stmtList(0xc0000036c0, 0x0, {0xc0001133c0?, 0xc0000a8c90?, 0xc99791?})
	cmd/compile/internal/types2/stmt.go:122 +0x85
cmd/compile/internal/types2.(*Checker).funcBody(0xc0000036c0, 0xc0004084e0?, {0xc000010db0?, 0x6954c772387e2e16?}, 0xc000464c40, 0xc000405200, {0x0?, 0x0?})
	cmd/compile/internal/types2/stmt.go:42 +0x310
cmd/compile/internal/types2.(*Checker).objDecl.(*Checker).funcDecl.func4()
	cmd/compile/internal/types2/decl.go:775 +0x3a
cmd/compile/internal/types2.(*Checker).processDelayed(0xc0000036c0, 0x0)
	cmd/compile/internal/types2/check.go:525 +0x211
cmd/compile/internal/types2.(*Checker).checkFiles(0xc0000036c0, {0xc0000786e0?, 0x167b400?, 0x167b928?})
	cmd/compile/internal/types2/check.go:467 +0x814
cmd/compile/internal/types2.(*Checker).Files(0x7ffce26d5fc5?, {0xc0000786e0?, 0x0?, 0x0?})
	cmd/compile/internal/types2/check.go:427 +0x75
cmd/compile/internal/types2.(*Config).Check(0xc00013d420, {0x7ffce26d5fc5?, 0xc0000100e7?}, {0xc0000786e0, 0x1, 0x1}, 0xc000408540)
	cmd/compile/internal/types2/api.go:488 +0x19d
cmd/compile/internal/noder.checkFiles({0x0, {0x0, 0x0}}, {0xc0000786c0, 0x1, 0xe59560?})
	cmd/compile/internal/noder/irgen.go:95 +0x5c9
cmd/compile/internal/noder.writePkgStub({0x0?, {0x0?, 0x0?}}, {0xc0000786c0, 0x1, 0x1})
	cmd/compile/internal/noder/unified.go:319 +0x6a
cmd/compile/internal/noder.unified({0x0?, {0x0?, 0x0?}}, {0xc0000786c0?, 0xddae60?, 0x0?})
	cmd/compile/internal/noder/unified.go:195 +0xb3
cmd/compile/internal/noder.LoadPackage({0xc000020260, 0x1, 0x2})
	cmd/compile/internal/noder/noder.go:77 +0x43a
cmd/compile/internal/gc.Main(0xeee068)
	cmd/compile/internal/gc/main.go:208 +0xcc5
main.main()
	cmd/compile/main.go:57 +0xf9
FAIL	github.com/(...)/validator [build failed]
FAIL

[dmitshur]

CC @golang/compiler.

[JunyangShao]

Thanks for finding the issue! I think the problem might be related to recursive type parameters:
I tried this smaller example and it panics with the same error:

package main

import (
        "fmt"
        "reflect"
)

type B[T any] struct {
        a A[T]
}

type A[T any] = func (B[T]) bool

func main() {
        var s A[int];

        fmt.Println(reflect.TypeOf(s))
}

However, changing the definition of A to be:

type A[T any] = struct {
        b B[T]
}

The compiler will error out with this message:

# command-line-arguments
./test3.go:9:4: invalid recursive type: B refers to itself

I guess the reason of this panic might be that the type recursion checker does not have a case for function types yet.
Looking into this further now...

[cuonglm]

Seems to be duplicated of #63285

[gopherbot]

Change https://go.dev/cl/668175 mentions this issue: cmd/compile: fix ICE with recursive alias type parameter