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cmd/go2go: panic in type checker #43526

candlerb opened this issue Jan 5, 2021 · 1 comment

cmd/go2go: panic in type checker #43526

candlerb opened this issue Jan 5, 2021 · 1 comment


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@candlerb candlerb commented Jan 5, 2021

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

go2go playground

Does this issue reproduce with the latest release?


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


What did you do?

package main

import (

type MyMap[KT, VT comparable] struct {
    data map[KT]VT

func NewMap[KT, VT comparable]() *MyMap[KT, VT] {
    var m MyMap[KT, VT] = make(map[KT]VT)
    return &m

func (m *MyMap[KT,VT]) set(k KT, v VT) {[k] = v

func main() {
    m := NewMap[string, int]
    m[int] = 123
    fmt.Println("Got ", m["foo"])

What did you expect to see?

An error message about the nonsense line m[int] = 123

What did you see instead?

Panic - from the type checker according to @ianlancetaylor here.

panic: assertion failed [recovered]
	panic: assertion failed [recovered]
	panic: assertion failed

goroutine 1 [running]:
go/types.(*Checker).handleBailout(0xc0000d4280, 0xc000159be0)
	/usr/local/go-faketime/src/go/types/check.go:252 +0x9b
panic(0x645460, 0x6d5ad0)
	/usr/local/go-faketime/src/runtime/panic.go:969 +0x175
go/types.(*Checker).stmt.func1(0xc0000d4280, 0xc00013db80)
	/usr/local/go-faketime/src/go/types/stmt.go:307 +0x85
panic(0x645460, 0x6d5ad0)
	/usr/local/go-faketime/src/runtime/panic.go:975 +0x3e9
go/types.(*Checker).call(0xc0000d4280, 0xc0000af180, 0xc00013def0, 0x6de1e0, 0xc000084fc0, 0x9)
	/usr/local/go-faketime/src/go/types/call.go:188 +0x172d
go/types.(*Checker).exprInternal(0xc0000d4280, 0xc0000af180, 0x6de1e0, 0xc000084fc0, 0x0, 0x0, 0x6462e0)
	/usr/local/go-faketime/src/go/types/expr.go:1359 +0x2b9e
go/types.(*Checker).rawExpr(0xc0000d4280, 0xc0000af180, 0x6de1e0, 0xc000084fc0, 0x0, 0x0, 0x0)
	/usr/local/go-faketime/src/go/types/expr.go:1043 +0xc5
go/types.(*Checker).expr(0xc0000d4280, 0xc0000af180, 0x6de1e0, 0xc000084fc0)
	/usr/local/go-faketime/src/go/types/expr.go:1753 +0x55
go/types.(*Checker).assignVar(0xc0000d4280, 0x6de1e0, 0xc000084fc0, 0xc0000af140, 0xc00013db00, 0xc0000a8328)
	/usr/local/go-faketime/src/go/types/assignments.go:176 +0x29b
go/types.(*Checker).assignVars(0xc0000d4280, 0xc000082820, 0x1, 0x1, 0xc000082830, 0x1, 0x1)
	/usr/local/go-faketime/src/go/types/assignments.go:283 +0x22f
go/types.(*Checker).stmt(0xc0000d4280, 0x0, 0x6ddae0, 0xc0000ae700)
	/usr/local/go-faketime/src/go/types/stmt.go:409 +0x351d
go/types.(*Checker).stmtList(0xc0000d4280, 0x0, 0xc0000ae740, 0x3, 0x4)
	/usr/local/go-faketime/src/go/types/stmt.go:125 +0xd1
go/types.(*Checker).funcBody(0xc0000d4280, 0xc00013e840, 0xc0000a445c, 0x4, 0xc00013ea20, 0xc000085020, 0x0, 0x0)
	/usr/local/go-faketime/src/go/types/stmt.go:42 +0x257
	/usr/local/go-faketime/src/go/types/decl.go:813 +0x67
go/types.(*Checker).processDelayed(0xc0000d4280, 0x0)
	/usr/local/go-faketime/src/go/types/check.go:327 +0x3e
go/types.(*Checker).checkFiles(0xc0000d4280, 0xc000105cb8, 0x1, 0x1, 0x0, 0x0)
	/usr/local/go-faketime/src/go/types/check.go:295 +0x205
go/types.(*Config).Check(0xc0000ae780, 0xc0000a43a0, 0x4, 0xc0000ae280, 0xc000105cb8, 0x1, 0x1, 0xc0000b1360, 0x0, 0x4b70cf, ...)
	/usr/local/go-faketime/src/go/types/api.go:392 +0x188
go/go2go.RewriteBuffer(0xc0000aa360, 0x7fff446f6dec, 0x1e, 0xc0000fa000, 0x174, 0x374, 0x0, 0xc000084a50, 0xc000084a20, 0xc0000849f0, ...)
	/usr/local/go-faketime/src/go/go2go/go2go.go:139 +0x257
main.translateFile(0xc0000aa360, 0x7fff446f6dec, 0x1e)
	/usr/local/go-faketime/src/cmd/go2go/translate.go:26 +0xa9
	/usr/local/go-faketime/src/cmd/go2go/main.go:74 +0x309
@ianlancetaylor ianlancetaylor changed the title go2: panic in type checker cmd/go2go: panic in type checker Jan 5, 2021
@ianlancetaylor ianlancetaylor added this to the Unreleased milestone Jan 5, 2021
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@griesemer griesemer commented Jan 5, 2021

This works fine with cmd/compile/internal/types2 and the compiler (dev.typeparams branch).

@griesemer griesemer modified the milestones: Unreleased, Go1.17 Jan 6, 2021
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