cmd/go2go: assertion failed in unifier.nify

[tdakkota]

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

$ go version
go version devel +34f76220c3 Sat Jul 4 04:55:49 2020 +0000 windows/amd64

Does this issue reproduce with the latest release?

n/a

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

• Go2go playground
• windows/amd64

What did you do?

https://go2goplay.golang.org/p/JXCEVdUcw-2

What did you expect to see?

Successful compilation or some error.
I don't know should or should't this example compile, but type checker should not panic.

What did you see instead?

Stack trace:

panic: assertion failed [recovered]
	panic: assertion failed

goroutine 1 [running]:
go/types.(*Checker).handleBailout(0xc0001046c0, 0xc000077be0)
	G:/workspace/exprm/go/src/go/types/check.go:251 +0x9f
panic(0x101ff20, 0x10b5700)
	G:/workspace/exprm/go/src/runtime/panic.go:969 +0x176
go/types.assert(...)
	G:/workspace/exprm/go/src/go/types/errors.go:19
go/types.(*unifier).nify(0xc000052780, 0x10c17a0, 0xc00003eba0, 0x10c1200, 0xc00007e2d0, 0x0, 0x0)
	G:/workspace/exprm/go/src/go/types/unify.go:368 +0x18e5
go/types.(*unifier).nify(0xc000052780, 0x10c15c0, 0xc00014e440, 0x10c15c0, 0xc00014ed00, 0x0, 0xf09093)
	G:/workspace/exprm/go/src/go/types/unify.go:261 +0xd07
go/types.(*unifier).nify(0xc000052780, 0x10c1340, 0xc00003eae0, 0x10c1340, 0xc00003f740, 0x0, 0xc000052780)
	G:/workspace/exprm/go/src/go/types/unify.go:278 +0xb3f
go/types.(*unifier).unify(0xc000052780, 0x10c1340, 0xc00003eae0, 0x10c1340, 0xc00003f740, 0xc00000a650)
	G:/workspace/exprm/go/src/go/types/unify.go:38 +0x65
go/types.(*Checker).missingMethod(0xc0001046c0, 0x10c1200, 0xc00007e2d0, 0xc00010a900, 0xc00014ec01, 0x10c10c0, 0xc00010a900)
	G:/workspace/exprm/go/src/go/types/lookup.go:418 +0x393
go/types.(*Checker).instantiate(0xc0001046c0, 0x306, 0x10c1340, 0xc00003f1a0, 0xc000153280, 0x4, 0x4, 0xc000010880, 0x4, 0x4, ...)
	G:/workspace/exprm/go/src/go/types/subst.go:165 +0x8b6
go/types.(*Checker).call(0xc0001046c0, 0xc000153140, 0xc00003d680, 0x1230e20)
	G:/workspace/exprm/go/src/go/types/call.go:116 +0x339
go/types.(*Checker).exprInternal(0xc0001046c0, 0xc000153140, 0x10bd540, 0xc00003d680, 0x0, 0x0, 0x10c12a0)
	G:/workspace/exprm/go/src/go/types/expr.go:1576 +0x1df0
go/types.(*Checker).rawExpr(0xc0001046c0, 0xc000153140, 0x10bd540, 0xc00003d680, 0x0, 0x0, 0x0)
	G:/workspace/exprm/go/src/go/types/expr.go:1033 +0xc7
go/types.(*Checker).exprOrType(0xc0001046c0, 0xc000153140, 0x10bd540, 0xc00003d680)
	G:/workspace/exprm/go/src/go/types/expr.go:1724 +0x5c
go/types.(*Checker).call(0xc0001046c0, 0xc000153140, 0xc00003d740, 0x230dcfab748)
	G:/workspace/exprm/go/src/go/types/call.go:17 +0x78
go/types.(*Checker).exprInternal(0xc0001046c0, 0xc000153140, 0x10bd540, 0xc00003d740, 0x0, 0x0, 0x38)
	G:/workspace/exprm/go/src/go/types/expr.go:1576 +0x1df0
go/types.(*Checker).rawExpr(0xc0001046c0, 0xc000153140, 0x10bd540, 0xc00003d740, 0x0, 0x0, 0x0)
	G:/workspace/exprm/go/src/go/types/expr.go:1033 +0xc7
go/types.(*Checker).stmt(0xc0001046c0, 0x0, 0x10bd7c0, 0xc000032e30)
	G:/workspace/exprm/go/src/go/types/stmt.go:330 +0x3e78
go/types.(*Checker).stmtList(0xc0001046c0, 0x0, 0xc000032e40, 0x1, 0x1)
	G:/workspace/exprm/go/src/go/types/stmt.go:125 +0xd6
go/types.(*Checker).funcBody(0xc0001046c0, 0xc00003e720, 0xc00000a6d8, 0x4, 0xc00003f440, 0xc000067e90, 0x0, 0x0)
	G:/workspace/exprm/go/src/go/types/stmt.go:42 +0x268
go/types.(*Checker).funcDecl.func1()
	G:/workspace/exprm/go/src/go/types/decl.go:792 +0x6e
go/types.(*Checker).processDelayed(0xc0001046c0, 0x0)
	G:/workspace/exprm/go/src/go/types/check.go:315 +0x45
go/types.(*Checker).checkFiles(0xc0001046c0, 0xc000077cb8, 0x1, 0x1, 0x0, 0x0)
	G:/workspace/exprm/go/src/go/types/check.go:283 +0x14d
go/types.(*Checker).Files(...)
	G:/workspace/exprm/go/src/go/types/check.go:256
go/types.(*Config).Check(0xc00003d780, 0xc00000a4d0, 0x4, 0xc00003c280, 0xc000077cb8, 0x1, 0x1, 0xc000041360, 0x0, 0xc000142000, ...)
	G:/workspace/exprm/go/src/go/types/api.go:387 +0x188
go/go2go.RewriteBuffer(0xc00003e2a0, 0xc00000e360, 0x26, 0xc000144000, 0x355, 0x555, 0x0, 0xc000066ba0, 0xc000066b70, 0xc000066b40, ...)
	G:/workspace/exprm/go/src/go/go2go/go2go.go:137 +0x25b
main.translateFile(0xc00003e2a0, 0xc00000e360, 0x26)
	G:/workspace/exprm/go/src/cmd/go2go/translate.go:26 +0xb0
main.main()
	G:/workspace/exprm/go/src/cmd/go2go/main.go:65 +0x30a

[thepudds]

Hi @tdakkota, thanks for filing this as well.

In the current version of the go2go playground, your example fails on an assertion in go/types.(*unifier).nify on line 351 of go/types/unify.go.

Just a quick comment that Crash 24 from #39634 (comment) also crashes on the same assert on the same line 351 of go/types/unify.go.

That said, the call stacks leading up to the assert are fairly different between your example vs. Crash 24, so might not be the same core issue.

In any event, just wanted to mention this in case it helps with triage.

Current playground stacktrace for @tdakkota example

panic: assertion failed [recovered]

panic: assertion failed
goroutine 1 [running]:

go/types.(*Checker).handleBailout(0xc000084900, 0xc0000f1be0)

/usr/local/go-faketime/src/go/types/check.go:251 +0x98

panic(0x6498a0, 0x6db5e0)

/usr/local/go-faketime/src/runtime/panic.go:969 +0x175

go/types.assert(...)

/usr/local/go-faketime/src/go/types/errors.go:19

go/types.(*unifier).nify(0xc000098780, 0x6e6f20, 0xc00004aae0, 0x6e6980, 0xc00007e240, 0x0, 0x0)

/usr/local/go-faketime/src/go/types/unify.go:351 +0x18c5

go/types.(*unifier).nify(0xc000098780, 0x6e6d40, 0xc00000d920, 0x6e6d40, 0xc0000e81a0, 0x0, 0x537953)

/usr/local/go-faketime/src/go/types/unify.go:244 +0xce7

go/types.(*unifier).nify(0xc000098780, 0x6e6ac0, 0xc00004aa20, 0x6e6ac0, 0xc00004b620, 0x0, 0xc000098780)

/usr/local/go-faketime/src/go/types/unify.go:261 +0xb1f

go/types.(*unifier).unify(0xc000098780, 0x6e6ac0, 0xc00004aa20, 0x6e6ac0, 0xc00004b620, 0xc00001a520)

/usr/local/go-faketime/src/go/types/unify.go:38 +0x5c

go/types.(*Checker).missingMethod(0xc000084900, 0x6e6980, 0xc00007e240, 0xc00008c980, 0xc0000e8101, 0x6e6840, 0xc00008c980)

/usr/local/go-faketime/src/go/types/lookup.go:418 +0x393

go/types.(*Checker).instantiate(0xc000084900, 0x296, 0x6e6ac0, 0xc00004b0e0, 0xc0000e4a40, 0x4, 0x4, 0xc000016400, 0x4, 0x4, ...)

/usr/local/go-faketime/src/go/types/subst.go:164 +0x896

go/types.(*Checker).call(0xc000084900, 0xc0000e4900, 0xc00007b240, 0x0)

/usr/local/go-faketime/src/go/types/call.go:109 +0x325

go/types.(*Checker).exprInternal(0xc000084900, 0xc0000e4900, 0x6e32a0, 0xc00007b240, 0x0, 0x0, 0xc00000d620)

/usr/local/go-faketime/src/go/types/expr.go:1569 +0x1dd0

go/types.(*Checker).rawExpr(0xc000084900, 0xc0000e4900, 0x6e32a0, 0xc00007b240, 0x0, 0x0, 0x0)

/usr/local/go-faketime/src/go/types/expr.go:1033 +0xc5

go/types.(*Checker).exprOrType(0xc000084900, 0xc0000e4900, 0x6e32a0, 0xc00007b240)

/usr/local/go-faketime/src/go/types/expr.go:1717 +0x55

go/types.(*Checker).call(0xc000084900, 0xc0000e4900, 0xc00007b300, 0x7f667791d6c0)

/usr/local/go-faketime/src/go/types/call.go:17 +0x69

go/types.(*Checker).exprInternal(0xc000084900, 0xc0000e4900, 0x6e32a0, 0xc00007b300, 0x0, 0x0, 0x38)

/usr/local/go-faketime/src/go/types/expr.go:1569 +0x1dd0

go/types.(*Checker).rawExpr(0xc000084900, 0xc0000e4900, 0x6e32a0, 0xc00007b300, 0x0, 0x0, 0x0)

/usr/local/go-faketime/src/go/types/expr.go:1033 +0xc5

go/types.(*Checker).stmt(0xc000084900, 0x0, 0x6e3520, 0xc00001cc50)

/usr/local/go-faketime/src/go/types/stmt.go:330 +0x3e78

go/types.(*Checker).stmtList(0xc000084900, 0x0, 0xc00001cc60, 0x1, 0x1)

/usr/local/go-faketime/src/go/types/stmt.go:125 +0xd1

go/types.(*Checker).funcBody(0xc000084900, 0xc00004a7e0, 0xc00001a5a8, 0x4, 0xc00004b380, 0xc0000118f0, 0x0, 0x0)

/usr/local/go-faketime/src/go/types/stmt.go:42 +0x257

go/types.(*Checker).funcDecl.func1()

/usr/local/go-faketime/src/go/types/decl.go:790 +0x67

go/types.(*Checker).processDelayed(0xc000084900, 0x0)

/usr/local/go-faketime/src/go/types/check.go:315 +0x3e

go/types.(*Checker).checkFiles(0xc000084900, 0xc0000c9cb8, 0x1, 0x1, 0x0, 0x0)

/usr/local/go-faketime/src/go/types/check.go:283 +0x145

go/types.(*Checker).Files(...)

/usr/local/go-faketime/src/go/types/check.go:256

go/types.(*Config).Check(0xc00007b340, 0xc00001a3e0, 0x4, 0xc00007a240, 0xc0000c9cb8, 0x1, 0x1, 0xc000055360, 0x0, 0x4b702f, ...)

/usr/local/go-faketime/src/go/types/api.go:387 +0x188

go/go2go.RewriteBuffer(0xc00004a3c0, 0x7ffe1dcd0dec, 0x1e, 0xc0000c2000, 0x2e5, 0x4e5, 0x0, 0xc000010a50, 0xc000010a20, 0xc0000109f0, ...)

/usr/local/go-faketime/src/go/go2go/go2go.go:137 +0x24f

main.translateFile(0xc00004a3c0, 0x7ffe1dcd0dec, 0x1e)

/usr/local/go-faketime/src/cmd/go2go/translate.go:26 +0xa9

main.main()

Current playground stacktrace for Crash 24 example

panic: assertion failed [recovered]
	panic: assertion failed
goroutine 1 [running]:

go/types.(*Checker).handleBailout(0xc00007c900, 0xc0000c3be0)

/usr/local/go-faketime/src/go/types/check.go:251 +0x98

panic(0x6498a0, 0x6db5e0)

/usr/local/go-faketime/src/runtime/panic.go:969 +0x175

go/types.assert(...)

/usr/local/go-faketime/src/go/types/errors.go:19

go/types.(*unifier).nify(0xc000090320, 0x6e6f20, 0xc00004a600, 0x6e6980, 0xc00007a240, 0x0, 0xc0000c1420)

/usr/local/go-faketime/src/go/types/unify.go:351 +0x18c5

go/types.(*unifier).unify(...)

/usr/local/go-faketime/src/go/types/unify.go:38

go/types.(*Checker).infer(0xc00007c900, 0x25, 0xc00000e0d8, 0x1, 0x1, 0xc0000c1730, 0xc0000c16e8, 0x1, 0x1, 0xc00001a430, ...)

/usr/local/go-faketime/src/go/types/infer.go:52 +0x36a

go/types.(*Checker).selector(0xc00007c900, 0xc000072600, 0xc00000c380)

/usr/local/go-faketime/src/go/types/call.go:529 +0xdfa

go/types.(*Checker).exprInternal(0xc00007c900, 0xc000072600, 0x6e3a20, 0xc00000c380, 0x0, 0x0, 0x0)

/usr/local/go-faketime/src/go/types/expr.go:1320 +0x29cc

go/types.(*Checker).rawExpr(0xc00007c900, 0xc000072600, 0x6e3a20, 0xc00000c380, 0x0, 0x0, 0x0)

/usr/local/go-faketime/src/go/types/expr.go:1033 +0xc5

go/types.(*Checker).exprOrType(0xc00007c900, 0xc000072600, 0x6e3a20, 0xc00000c380)

/usr/local/go-faketime/src/go/types/expr.go:1717 +0x55

go/types.(*Checker).call(0xc00007c900, 0xc000072600, 0xc0000723c0, 0x0)

/usr/local/go-faketime/src/go/types/call.go:17 +0x69

go/types.(*Checker).exprInternal(0xc00007c900, 0xc000072600, 0x6e32a0, 0xc0000723c0, 0x0, 0x0, 0x0)

/usr/local/go-faketime/src/go/types/expr.go:1569 +0x1dd0

go/types.(*Checker).rawExpr(0xc00007c900, 0xc000072600, 0x6e32a0, 0xc0000723c0, 0x0, 0x0, 0x0)

/usr/local/go-faketime/src/go/types/expr.go:1033 +0xc5

go/types.(*Checker).multiExpr(0xc00007c900, 0xc000072600, 0x6e32a0, 0xc0000723c0)

/usr/local/go-faketime/src/go/types/expr.go:1692 +0x51

go/types.(*Checker).exprList(0xc00007c900, 0xc00001c580, 0x1, 0x1, 0x81bb00, 0x7fe5ecc14108, 0x0, 0x50, 0xc000055860)

/usr/local/go-faketime/src/go/types/call.go:206 +0xb4

go/types.(*Checker).initVars(0xc00007c900, 0xc00000e0f8, 0x1, 0x1, 0xc00001c580, 0x1, 0x1, 0x0)

/usr/local/go-faketime/src/go/types/assignments.go:214 +0x94

go/types.(*Checker).shortVarDecl(0xc00007c900, 0x35, 0xc00001c560, 0x1, 0x1, 0xc00001c580, 0x1, 0x1)

/usr/local/go-faketime/src/go/types/assignments.go:326 +0x27e

go/types.(*Checker).stmt(0xc00007c900, 0x0, 0x6e30a0, 0xc000072400)

/usr/local/go-faketime/src/go/types/stmt.go:403 +0x351d

go/types.(*Checker).stmtList(0xc00007c900, 0x0, 0xc00001c590, 0x1, 0x1)

/usr/local/go-faketime/src/go/types/stmt.go:125 +0xd1

go/types.(*Checker).funcBody(0xc00007c900, 0xc00004a540, 0x809ce8, 0x1, 0xc00004a5a0, 0xc000010c00, 0x0, 0x0)

/usr/local/go-faketime/src/go/types/stmt.go:42 +0x257

go/types.(*Checker).funcDecl.func1()

/usr/local/go-faketime/src/go/types/decl.go:790 +0x67

go/types.(*Checker).processDelayed(0xc00007c900, 0x0)

/usr/local/go-faketime/src/go/types/check.go:315 +0x3e

go/types.(*Checker).checkFiles(0xc00007c900, 0xc00003dcb8, 0x1, 0x1, 0x0, 0x0)

/usr/local/go-faketime/src/go/types/check.go:283 +0x145

go/types.(*Checker).Files(...)

/usr/local/go-faketime/src/go/types/check.go:256

go/types.(*Config).Check(0xc000072440, 0xc00001a3e0, 0x4, 0xc000072240, 0xc00003dcb8, 0x1, 0x1, 0xc000055360, 0x0, 0x4b702f, ...)

/usr/local/go-faketime/src/go/types/api.go:387 +0x188

go/go2go.RewriteBuffer(0xc00004a3c0, 0x7ffd9c5d6dec, 0x1e, 0xc0000ba000, 0x3f, 0x23f, 0x0, 0xc000010a50, 0xc000010a20, 0xc0000109f0, ...)

/usr/local/go-faketime/src/go/go2go/go2go.go:137 +0x24f

main.translateFile(0xc00004a3c0, 0x7ffd9c5d6dec, 0x1e)

/usr/local/go-faketime/src/cmd/go2go/translate.go:26 +0xa9

main.main()

cc @griesemer

[tdakkota]

I tried change

go/src/go/types/unify.go

Lines 363 to 368 in 9d9619a

	if y, ok := y.(*Named); ok {
	// TODO(gri) This is not always correct: two types may have the same names
	// in the same package if one of them is nested in a function.
	// Extremely unlikely but we need an always correct solution.
	if x.obj.pkg == y.obj.pkg && x.obj.name == y.obj.name {
	assert(len(x.targs) == len(y.targs))

to

		if y, ok := y.(*Named); ok {
			// TODO(gri) This is not always correct: two types may have the same names
			//           in the same package if one of them is nested in a function.
			//           Extremely unlikely but we need an always correct solution.
			if x.obj.pkg == y.obj.pkg && x.obj.name == y.obj.name {
				if len(x.targs) != len(y.targs) {
					return false
				}

It's should fix both crash cases.

It happens because type checker fails to infer types

func main() {
	Map(string, int, Optional, Optional)("1", func(s string) int { // here: Optional(T)
		return 1
	})
}                               

and

package main
type C(type P) P
func (r C(P)) m() { y := C.m() } // here: C(P)

[gopherbot]

Change https://golang.org/cl/247498 mentions this issue: [dev.go2go] go/types: fix instantiation crash for generic type parame…

[griesemer]

Fixed by https://golang.org/cl/247498.

[gopherbot]

Change https://golang.org/cl/248058 mentions this issue: [dev.go2go] cmd/compile/internal/types2: fix instantiation crash for generic type parameters