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cmd/go2go: infinite recursion in generics type checker #39695

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ianlancetaylor opened this issue Jun 18, 2020 · 2 comments
Open

cmd/go2go: infinite recursion in generics type checker #39695

ianlancetaylor opened this issue Jun 18, 2020 · 2 comments
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@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Jun 18, 2020

Passing this program through the go2go tool produces an infinite recursion in go/types.

package main

import (
	"fmt"
	"unsafe"
)

type EmbedringConstraint(type T interface{}) interface {
	Parent() *T
}

type Deembeder(type T interface{}, ER EmbedringConstraint(T)) interface {
	Deembed(*ER) *T
}

type Embedring(type T interface{}, DE Deembeder(T, EmbedringConstraint(T))) struct {
	prev, next *Embedring(T, DE)
}

func (ring *Embedring(T, DE)) Parent() *T {
	var de DE
	return de.Deembed(ring)
}

type Foo struct {
	name  string
	ring1 Embedring(Foo, FooRing1)
	ring2 Embedring(Foo, FooRing2)
}

type FooRing1 struct{}

func (_ FooRing1) Deembed(ring *Embedring(Foo, FooRing1)) *Foo {
	return deembed(ring, unsafe.Offsetof(Foo{}.ring1))
}

type FooRing2 struct{}

func (_ FooRing2) Deembed(ring *Embedring(Foo, FooRing2)) *Foo {
	return deembed(ring, unsafe.Offsetof(Foo{}.ring2))
}

func deembed(type T interface{}, ER Embedring(T))(ring *ER, offsetof uintptr) *T {
	return (*T)(unsafe.Pointer(uintptr(unsafe.Pointer(ring)) - offsetof))
}

func main() {
	var foo Foo
	foo.name = "Hello"

	fmt.Println(foo.ring1.Parent().name)
	fmt.Println(foo.ring2.Parent().name)
}

Partial stack trace:

``` runtime: goroutine stack exceeds 1000000000-byte limit runtime: sp=0xc0205804a0 stack=[0xc020580000, 0xc040580000] fatal error: stack overflow

runtime stack:
runtime.throw(0x69320d, 0xe)
/home/iant/gogen/src/runtime/panic.go:1116 +0x72
runtime.newstack()
/home/iant/gogen/src/runtime/stack.go:1059 +0x78d
runtime.morestack()
/home/iant/gogen/src/runtime/asm_amd64.s:449 +0x8f

goroutine 1 [running]:
go/types.(*subster).typ(0xc020581128, 0x6ded40, 0xc000124bd0, 0x0, 0x0)
/home/iant/gogen/src/go/types/subst.go:239 +0x226c fp=0xc0205804b0 sp=0xc0205804a8 pc=0x56ab6c
go/types.(*subster).typ(0xc020581128, 0x6dede0, 0xc0001aee20, 0x0, 0x0)
/home/iant/gogen/src/go/types/subst.go:265 +0x2106 fp=0xc020580828 sp=0xc0205804b0 pc=0x56aa06
go/types.(*subster).var_(0xc020581128, 0xc0001ba500, 0x40d3b0)
/home/iant/gogen/src/go/types/subst.go:438 +0x5a fp=0xc020580878 sp=0xc020580828 pc=0x56ae3a
go/types.(*subster).varList(0xc020581128, 0xc000102438, 0x1, 0x1, 0xc020580948, 0x55267a, 0xc00ad2c8d0, 0x4cf699)
/home/iant/gogen/src/go/types/subst.go:459 +0x98 fp=0xc0205808e8 sp=0xc020580878 pc=0x56b0f8
go/types.(*subster).tuple(0xc020581128, 0xc0001aee40, 0xc00011e4d8)
/home/iant/gogen/src/go/types/subst.go:449 +0x65 fp=0xc020580950 sp=0xc0205808e8 pc=0x56afc5
go/types.(*subster).typ(0xc020581128, 0x6dee80, 0xc0001b3020, 0x0, 0x0)
/home/iant/gogen/src/go/types/subst.go:277 +0x154a fp=0xc020580cc8 sp=0xc020580950 pc=0x569e4a
go/types.(*subster).func_(0xc020581128, 0xc0001ba5a0, 0x0)
/home/iant/gogen/src/go/types/subst.go:476 +0x5a fp=0xc020580d18 sp=0xc020580cc8 pc=0x56b27a
go/types.(*subster).funcList(0xc020581128, 0xc000102448, 0x1, 0x1, 0x0, 0x8, 0x0, 0xc00d5eba40)
/home/iant/gogen/src/go/types/subst.go:488 +0x98 fp=0xc020580d88 sp=0xc020580d18 pc=0x56b438
go/types.(*subster).typ(0xc020581128, 0x6dec00, 0xc000130c00, 0x0, 0x0)
/home/iant/gogen/src/go/types/subst.go:301 +0x175e fp=0xc020581100 sp=0xc020580d88 pc=0x56a05e
go/types.(*Checker).subst(0xc0001265a0, 0x246, 0x6dec00, 0xc000130c00, 0xc00d692d00, 0x2, 0xc00d692d00)
/home/iant/gogen/src/go/types/subst.go:229 +0x11b fp=0xc020581158 sp=0xc020581100 pc=0x56885b
go/types.(*Checker).instantiate(0xc0001265a0, 0x237, 0x6ded40, 0xc000124b40, 0xc0001af4e0, 0x2, 0x2, 0xc00011eff0, 0x2, 0x2, ...)
/home/iant/gogen/src/go/types/subst.go:138 +0x29f fp=0xc020581350 sp=0xc020581158 pc=0x5678bf
go/types.(*instance).expand(0xc0001b33e0, 0x0, 0x0)
/home/iant/gogen/src/go/types/type.go:890 +0xed fp=0xc0205813c0 sp=0xc020581350 pc=0x56e12d
go/types.expand(...)
/home/iant/gogen/src/go/types/type.go:908
go/types.(*unifier).nify(0xc00d682b40, 0x6df2e0, 0xc0001b33e0, 0x6ded40, 0xc000125560, 0x0, 0x0)
/home/iant/gogen/src/go/types/unify.go:94 +0x17c6 fp=0xc020581568 sp=0xc0205813c0 pc=0x57bfa6
go/types.(*unifier).nify(0xc00d682b40, 0x6dede0, 0xc0001af4c0, 0x6dede0, 0xc00d692c60, 0x0, 0xc0205817a8)
/home/iant/gogen/src/go/types/unify.go:233 +0x106a fp=0xc020581710 sp=0xc020581568 pc=0x57b84a
go/types.(*unifier).nify(0xc00d682b40, 0x6df100, 0xc0001af560, 0x6df100, 0xc00d692c80, 0x0, 0x0)
/home/iant/gogen/src/go/types/unify.go:244 +0xd87 fp=0xc0205818b8 sp=0xc020581710 pc=0x57b567
go/types.(*unifier).nify(0xc00d682b40, 0x6dee80, 0xc0001b3380, 0x6dee80, 0xc00eb66000, 0x0, 0xc00d682b40)
/home/iant/gogen/src/go/types/unify.go:261 +0xbbf fp=0xc020581a60 sp=0xc0205818b8 pc=0x57b39f
go/types.(*unifier).unify(0xc00d682b40, 0x6dee80, 0xc0001b3380, 0x6dee80, 0xc00eb66000, 0xc00011e439)
/home/iant/gogen/src/go/types/unify.go:38 +0x5c fp=0xc020581aa8 sp=0xc020581a60 pc=0x57a7bc
go/types.(*Checker).missingMethod(0xc0001265a0, 0x6ded40, 0xc000125320, 0xc00d66da00, 0xc00d692c01, 0x6dec00, 0xc00d66da00)
/home/iant/gogen/src/go/types/lookup.go:409 +0x305 fp=0xc020581ba8 sp=0xc020581aa8 pc=0x5508e5
go/types.(*Checker).instantiate(0xc0001265a0, 0x237, 0x6ded40, 0xc000124b40, 0xc0001af4e0, 0x2, 0x2, 0xc00011eff0, 0x2, 0x2, ...)
/home/iant/gogen/src/go/types/subst.go:164 +0x896 fp=0xc020581da0 sp=0xc020581ba8 pc=0x567eb6
go/types.(*instance).expand(0xc0001b33e0, 0x0, 0x0)
/home/iant/gogen/src/go/types/type.go:890 +0xed fp=0xc020581e10 sp=0xc020581da0 pc=0x56e12d
go/types.expand(...)
/home/iant/gogen/src/go/types/type.go:908
go/types.(*unifier).nify(0xc00d682aa0, 0x6df2e0, 0xc0001b33e0, 0x6ded40, 0xc000125560, 0x0, 0x0)
/home/iant/gogen/src/go/types/unify.go:94 +0x17c6 fp=0xc020581fb8 sp=0xc020581e10 pc=0x57bfa6
...

</details>
@beoran
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@beoran beoran commented Jun 18, 2020

Perhaps this is related to #39688?

@griesemer
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@griesemer griesemer commented Jun 19, 2020

Not related to #39688 .

Simpler reproducer:

package p

type D interface {
	m(*int)
}

type E(type _ D) struct {}

type F struct{}

func (F) m(*E(F))

The code type-checks if we remove the two *.

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