Golang cmd/compile/internal/types2: unify.go:449: assertion failed, panic

Go version

go version devel go1.23-cf501e05e1 Thu Jun 6 21:59:21 2024 +0000 darwin/arm64

Output of `go env` in your module/workspace:

GO111MODULE='off'
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/kburke/Library/Caches/go-build'
GOENV='/Users/kburke/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/kburke/pkg/mod'
GONOPROXY='github.com/segmentio'
GONOSUMDB='github.com/segmentio'
GOOS='darwin'
GOPATH='/Users/kburke'
GOPRIVATE='github.com/segmentio'
GOPROXY='direct'
GOROOT='/Users/kburke/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/kburke/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='devel go1.23-cf501e05e1 Thu Jun 6 21:59:21 2024 +0000'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/kburke/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD=''
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 -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/9s/w0d5_1fx71j5f225g95vtx340000gn/T/go-build3319341203=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

Attempted to run "go vet" or "golangci-lint" on company source code

What did you see happen?

I got the following stack trace. Unfortunately, I don't have time to dig into it or try to bisect the problem, but maybe the stack trace is enough of a clue.

<unknown line number>: internal compiler error: panic: ../../../../go/src/cmd/compile/internal/types2/unify.go:449: assertion failed

goroutine 1 [running]:
runtime/debug.Stack()
    ../../../../go/src/runtime/debug/stack.go:26 +0x64
cmd/compile/internal/base.FatalfAt({0x9cda18?, 0x140?}, {0x104a5aa79, 0x9}, {0x140009cda48, 0x1, 0x1})
    ../../../../go/src/cmd/compile/internal/base/print.go:230 +0x20c
cmd/compile/internal/base.Fatalf(...)
    ../../../../go/src/cmd/compile/internal/base/print.go:195
cmd/compile/internal/gc.handlePanic()
    ../../../../go/src/cmd/compile/internal/gc/main.go:53 +0x8c
panic({0x104c74f40?, 0x14000a4e100?})
    ../../../../go/src/runtime/panic.go:785 +0x124
cmd/compile/internal/types2.(*Checker).handleBailout(0x1400036e700, 0x140009d10d8)
    ../../../../go/src/cmd/compile/internal/types2/check.go:390 +0x9c
panic({0x104c74f40?, 0x14000a4e100?})
    ../../../../go/src/runtime/panic.go:785 +0x124
cmd/compile/internal/types2.assert(0xf8?)
    ../../../../go/src/cmd/compile/internal/types2/errors.go:25 +0x60
cmd/compile/internal/types2.(*unifier).nify(0x140009fd3f8, {0x104d65b68, 0x1400095d180}, {0x104d65c80, 0x1400095fa80}, 0x0, 0x0)
    ../../../../go/src/cmd/compile/internal/types2/unify.go:449 +0x820
cmd/compile/internal/types2.(*unifier).unify(...)
    ../../../../go/src/cmd/compile/internal/types2/unify.go:141
cmd/compile/internal/types2.(*Checker).infer(0x1400036e700, {0x1400058e2a0, 0x6e, 0x13}, {0x14000a4e070, 0x2, 0x2}, {0x140009c56c0, 0x2, 0x2}, ...)
    ../../../../go/src/cmd/compile/internal/types2/infer.go:255 +0x8b0
cmd/compile/internal/types2.(*Checker).arguments(0x1400036e700, 0x140005b4d20, 0x140009c9940, {0x0, 0x0, 0x0}, {0x0, 0x0, 0x0}, {0x14000a4e040, ...}, ...)
    ../../../../go/src/cmd/compile/internal/types2/call.go:608 +0x9a4
cmd/compile/internal/types2.(*Checker).callExpr(0x1400036e700, 0x14000a4c540, 0x140005b4d20)
    ../../../../go/src/cmd/compile/internal/types2/call.go:295 +0x46c
cmd/compile/internal/types2.(*Checker).exprInternal(0x1400036e700, 0x0, 0x14000a4c540, {0x104d6ae00, 0x140005b4d20}, {0x0, 0x0})
    ../../../../go/src/cmd/compile/internal/types2/expr.go:1431 +0xbc
cmd/compile/internal/types2.(*Checker).rawExpr(0x1400036e700, 0x0, 0x14000a4c540, {0x104d6ae00?, 0x140005b4d20?}, {0x0?, 0x0?}, 0x0)
    ../../../../go/src/cmd/compile/internal/types2/expr.go:996 +0x128
cmd/compile/internal/types2.(*Checker).multiExpr(0x1400036e700, {0x104d6ae00, 0x140005b4d20}, 0x0)
    ../../../../go/src/cmd/compile/internal/types2/expr.go:1621 +0x60
cmd/compile/internal/types2.(*Checker).initVars(0x1400036e700, {0x14000a3e378, 0x1, 0x1}, {0x140009cfc28, 0x1, 0x1}, {0x0, 0x0})
    ../../../../go/src/cmd/compile/internal/types2/assignments.go:422 +0x100
cmd/compile/internal/types2.(*Checker).shortVarDecl(...)
    ../../../../go/src/cmd/compile/internal/types2/assignments.go:570
cmd/compile/internal/types2.(*Checker).stmt(0x1400036e700, 0x3, {0x104d68728, 0x140005c29c0})
    ../../../../go/src/cmd/compile/internal/types2/stmt.go:466 +0x1898
cmd/compile/internal/types2.(*Checker).stmtList(0x1400036e700, 0x3, {0x140005c6100?, 0x104a53bc8?, 0x5?})
    ../../../../go/src/cmd/compile/internal/types2/stmt.go:120 +0x88
cmd/compile/internal/types2.(*Checker).stmt(0x1400036e700, 0x3, {0x104d685d8, 0x140005c2800})
    ../../../../go/src/cmd/compile/internal/types2/stmt.go:554 +0x628
cmd/compile/internal/types2.(*Checker).rangeStmt(0x1400036e700, 0x3, 0x140005ca000, 0x104d6f700?)
    ../../../../go/src/cmd/compile/internal/types2/stmt.go:998 +0x534
cmd/compile/internal/types2.(*Checker).stmt(0x1400036e700, 0x0, {0x104d687d0, 0x140005ca000})
    ../../../../go/src/cmd/compile/internal/types2/stmt.go:642 +0x43c
cmd/compile/internal/types2.(*Checker).stmtList(0x1400036e700, 0x0, {0x140005be700?, 0x14000a3e258?, 0x0?})
    ../../../../go/src/cmd/compile/internal/types2/stmt.go:120 +0x88
cmd/compile/internal/types2.(*Checker).funcBody(0x1400036e700, 0x140005c99f0?, {0x140005ae350?, 0x1400058e2a0?}, 0x140009bb100, 0x140005c26c0, {0x0?, 0x0?})
    ../../../../go/src/cmd/compile/internal/types2/stmt.go:40 +0x218
cmd/compile/internal/types2.(*Checker).funcDecl.func1()
    ../../../../go/src/cmd/compile/internal/types2/decl.go:789 +0x44
cmd/compile/internal/types2.(*Checker).processDelayed(0x1400036e700, 0x0)
    ../../../../go/src/cmd/compile/internal/types2/check.go:502 +0x150
cmd/compile/internal/types2.(*Checker).checkFiles(0x1400036e700, {0x14000642000, 0x17, 0x17})
    ../../../../go/src/cmd/compile/internal/types2/check.go:448 +0x5c8
cmd/compile/internal/types2.(*Checker).Files(0x16bd96383?, {0x14000642000?, 0x0?, 0x0?})
    ../../../../go/src/cmd/compile/internal/types2/check.go:408 +0x80
cmd/compile/internal/types2.(*Config).Check(0x140006371f0, {0x16bd96383?, 0x1400000e0b7?}, {0x14000642000, 0x17, 0x17}, 0x1400063e5a0)
    ../../../../go/src/cmd/compile/internal/types2/api.go:480 +0x68
cmd/compile/internal/noder.checkFiles({0x0, {0x0, 0x0}}, {0x140000ee300, 0x17, 0x1044f3250?})
    ../../../../go/src/cmd/compile/internal/noder/irgen.go:95 +0x4b4
cmd/compile/internal/noder.writePkgStub({0x0?, {0x0?, 0x0?}}, {0x140000ee300, 0x17, 0x17})
    ../../../../go/src/cmd/compile/internal/noder/unified.go:307 +0x48
cmd/compile/internal/noder.unified({0x0?, {0x0?, 0x0?}}, {0x140000ee300?, 0x104c5d740?, 0x0?})
    ../../../../go/src/cmd/compile/internal/noder/unified.go:183 +0x98
cmd/compile/internal/noder.LoadPackage({0x1400001e3d8, 0x17, 0x1a})
    ../../../../go/src/cmd/compile/internal/noder/noder.go:77 +0x398
cmd/compile/internal/gc.Main(0x104d5da30)
    ../../../../go/src/cmd/compile/internal/gc/main.go:200 +0xb4c
main.main()
    ../../../../go/src/cmd/compile/main.go:57 +0x110) (typecheck)

What did you expect to see?

I expected to see vet emit output. I cannot reproduce the problem with Go 1.22.

Comment From: mknyszek

CC @golang/compiler

Comment From: mknyszek

This seems new in Go 1.23.

Comment From: rsc

These assertion failures should be improved to at least report the line number of the source code causing the assertion. That would let users try to trim down the code to a repro case. As it is, all they get is "somewhere there is a problem".

As the FAQ says, "[Assertions] are undeniably convenient, but our experience has been that programmers use them as a crutch to avoid thinking about proper error handling and reporting. Proper error handling means that servers continue to operate instead of crashing after a non-fatal error. Proper error reporting means that errors are direct and to the point, saving the programmer from interpreting a large crash trace. Precise errors are particularly important when the programmer seeing the errors is not familiar with the code."

The compiler needs to do better here.

Comment From: gabyhelp

Similar Issues

https://github.com/golang/go/issues/65778
https://github.com/golang/go/issues/40038
https://github.com/golang/go/issues/61486
https://github.com/golang/go/issues/64106
https://github.com/golang/go/issues/17716

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

Comment From: kevinburke

I was able to isolate the panic to a single private file which I emailed to Russ and Michael.

Comment From: griesemer

@kevinburke Hi Kevin, can you please share the single private file with me (gri@golang.org). I introduced the offending assert. Thanks.

Comment From: griesemer

@kevinburke No need for the private file anymore.

Reproducer:

package p

type A = uint8
type E uint8

func f[P A](P) {}

func g(e E) {
    f(e)
}

Comment From: gopherbot

Change https://go.dev/cl/591975 mentions this issue: go/types, types2: add missing Unalias calls in type unifier

Comment From: griesemer

@kevinburke I am fairly certain the above CL fixes the issue you see in your larger program (it was a bug in the type unifier) - but please check as soon as this issue is closed (and thus the fix is submitted), thanks. I have only verified for the simplified reproducer.

Comment From: griesemer

@rsc Filed #67932 to address https://github.com/golang/go/issues/67872#issuecomment-2155783254 (we were planning to do this a while ago but never quite got around to it).

Comment From: kevinburke

Confirmed no more panic! Vet completes successfully. Thanks for the fast fix.

Golang cmd/compile/internal/types2: unify.go:449: assertion failed, panic

Go version

Output of go env in your module/workspace:

What did you do?

What did you see happen?

What did you expect to see?

Output of `go env` in your module/workspace: