cmd/compile: ambiguous selector with generic interface & embedded types #53419

phemmer · 2022-06-17T02:31:56Z

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

$ go version
go version go1.18.3 linux/amd64

Does this issue reproduce with the latest release?

yes

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

go env Output

$ go env
GOARCH="amd64"
GOOS="linux"

What did you do?

package main

import "fmt"

type MyString string
type MyByteSlice []byte
type Both struct {
	MyString
	MyByteSlice
}

func (s1 MyString) Concat(s2 MyString) MyString            { return s1 + s2 }
func (bs1 MyByteSlice) Concat(bs2 MyByteSlice) MyByteSlice { return append(bs1, bs2...) }
func (b1 Both) Concat(b2 Both) Both {
	return Both{
		b1.MyString.Concat(b2.MyString),
		b1.MyByteSlice.Concat(b2.MyByteSlice),
	}
}

type Concatable[T any] interface {
	Concat(T) T
}

func Repeat[T Concatable[T]](c T) T {
	return c.Concat(c)
}

func main() {
	s := MyString("foo")
	bs := MyByteSlice("foo")
	b := Both{MyString("foo"), MyByteSlice("foo")}
	fmt.Println(Repeat(s))
	fmt.Println(Repeat(bs))
	fmt.Println(Repeat(b))
}

https://go.dev/play/p/Jyws-pz9k5X

What did you expect to see?

successful compilation

What did you see instead?

./prog.go:26:10: ambiguous selector c.Concat

Go build failed.

The error is with the Both type (as if I remove it, the issue goes away). However on Both, Concat is not ambiguous. Both has it's own Concat method, and should not be trying to fall through to either of the embedded types.

The text was updated successfully, but these errors were encountered:

thanm · 2022-06-17T14:14:39Z

@griesemer

griesemer · 2022-06-17T18:41:30Z

Simplified reproducer:

package main

type T1 struct{}
type T2 struct{}
type Both struct {
	T1
	T2
}

func (T1) m()   {}
func (T2) m()   {}
func (Both) m() {}

func f[T interface{ m() }](c T) {
	c.m()
}

func main() {
	var b Both
	// b.m()         // <<< this (without the f(b) below) is ok
	f(b)
}

The type checker (types2) doesn't have a problem with this, the error appears to arrive later, in the noder or after instantiation in the compiler (have not yet investigated).

@mdempsky Can you confirm that this problem is present/absent with unified IR?

mdempsky · 2022-06-17T18:46:06Z

@mdempsky Can you confirm that this problem is present/absent with unified IR?

Yeah, the test program appears to run correctly with GOEXPERIMENT=unified go run.

griesemer · 2022-06-17T22:17:07Z

Thanks, @mdempsky .
Unless we hear otherwise from users, we can probably just wait for the unified IR to fix this in 1.20.
Assigning to you and I for now so it's on the radar.

gopherbot · 2022-06-17T22:24:01Z

Change https://go.dev/cl/413014 mentions this issue: test: add regress test for #53419

This currently works with GOEXPERIMENT=unified. Add a regress test to make sure it stays that way. Updates #53419. Change-Id: I2ea1f9039c59807fbd497d69a0420771f8d6d035 Reviewed-on: https://go-review.googlesource.com/c/go/+/413014 Run-TryBot: Matthew Dempsky <mdempsky@google.com> Auto-Submit: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Robert Griesemer <gri@google.com> TryBot-Result: Gopher Robot <gobot@golang.org>

gopherbot · 2022-06-24T20:51:13Z

Change https://go.dev/cl/413977 mentions this issue: [dev.unified] all: merge master (5a1c5b8) into dev.unified

Conflicts: - test/run.go Textual conflict adding to the known failures list for the nounified frontend. Merge List: + 2022-06-24 5a1c5b8 cmd/go: add per-package indexing for modules outside mod cache + 2022-06-24 b9c4d94 cmd/go/internal/list: update help info with Deprecated field + 2022-06-24 73475ef go/types, types2: print qualified object names in cycle errors + 2022-06-24 3e58ef6 go/types, types2: better errors for == when type sets are empty + 2022-06-24 d38f1d1 doc/go1.19: Linux race detector now requires glibc 2.17 + 2022-06-23 de5329f debug/dwarf: handle malformed line table with bad program offset + 2022-06-23 15605ca embed: document additional file name restrictions + 2022-06-22 2e773a3 test: add test that causes gofrontend crash + 2022-06-22 ff17b7d cmd/compile: don't use dictionary convert to shaped empty interface + 2022-06-22 2a3b467 cmd/go: make module .zip files group/world readable + 2022-06-22 bdab4cf cmd/go, cmd/link: support failure to create _cgo_import.go + 2022-06-22 aca37d1 cmd/go: avoid indexing modules in GOROOT + 2022-06-22 111cdb5 all: update to current golang.org/x/sys revision + 2022-06-22 4045b1b cmd/compile: fix assert condition in generic method call + 2022-06-22 6bad7e8 compress/gzip: always close bodyReader in Example_compressingReader + 2022-06-22 606c6c3 encoding/xml: check nil pointer in DecodeElement + 2022-06-22 f571518 cmd/cgo: dont override declared struct type + 2022-06-22 92c9b81 net: don't set netGo = true on Windows with no cgo + 2022-06-22 be0b2a3 cmd/trace: add basic documentation to main page + 2022-06-22 b004c73 go/types, types2: fix parameter order dependence in type inference + 2022-06-21 f2c7e78 spec: document operations which accept []byte|string constrained types + 2022-06-21 ab422f2 runtime/trace: ignore fallback stacks in test + 2022-06-21 66685fb doc/go1.19: use correct link to sync/atomic docs + 2022-06-21 4b236b4 runtime: convert flaky semaphore linearity test into benchmark + 2022-06-21 530511b cmd/go/internal/modindex: avoid walking modules when not needed + 2022-06-21 c2d373d cmd/compile: allow 128-bit values to be spilled + 2022-06-21 19ed442 test: add regress test for #53477 + 2022-06-20 3fcbfb0 doc/go1.19: fix HTML validation issues + 2022-06-18 527ace0 cmd/compile: skip substituting closures in unsafe builtins arguments + 2022-06-17 ec58e3f test: add regress test for #53419 + 2022-06-17 103cc66 cmd/go/internal/modfetch: prevent duplicate hashes in go.sum + 2022-06-17 d42a488 sync: add more notes about Cond behavior + 2022-06-17 9e2f289 cmd/go/internal/work: log clearer detail for subprocess errors in (*Builder).toolID + 2022-06-17 dd2d00f net: fix flaky *TimeoutMustNotReturn tests + 2022-06-17 6c25ba6 go/token: delete unused File.set field + 2022-06-16 9068c68 cmd/dist: add package . to 'go test' commands + 2022-06-16 7bad615 runtime: write much more direct test for semaphore waiter scalability + 2022-06-16 f38a580 cmd/go: add more tracing Change-Id: I912c5879165e03f4d7f8ac3ee9241d50fc92a419

gopherbot · 2022-06-28T19:14:54Z

Change https://go.dev/cl/414836 mentions this issue: cmd/compile: only check implicit dots for method call enabled by a type bound

cuonglm · 2022-06-28T19:17:37Z

@mdempsky @griesemer I sent CL 414836 to fix this issue, is it worth to make it fixed for go1.19 or just wait for unified IR in go1.20 like you said above?

griesemer · 2022-07-01T18:20:17Z

@cuonglm The fix seems simple enough, but we're also close to RC1. I will ping the compiler/runtime team to chime in.

randall77 · 2022-07-06T20:31:13Z

@gopherbot please open a backport issue for 1.18.

gopherbot · 2022-07-06T20:31:28Z

Backport issue(s) opened: #53723 (for 1.18).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

gopherbot · 2022-08-09T12:43:29Z

Change https://go.dev/cl/422274 mentions this issue: cmd/compile: fix ICE when checking implicit dot for method call

…pe bound Fixes golang#53419 Change-Id: Ibad64f5c4af2112deeb0a9ecc9c589b17594bd05 Reviewed-on: https://go-review.googlesource.com/c/go/+/414836 Reviewed-by: Matthew Dempsky <mdempsky@google.com> Reviewed-by: David Chase <drchase@google.com> Reviewed-by: Keith Randall <khr@golang.org> TryBot-Result: Gopher Robot <gobot@golang.org> Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>

CL 414836 limited the check for implicit dot for method call enabled by a type bound. However, the checking condition for ODOTMETH only is not right. For example, for promoted method, we have a OXDOT node instead, and we still have to check for implicit dot in this case. However, if the base type and embedded types have the same method name, e.g in issue #53419, typecheck.AddImplicitDots will be confused and result in an ambigus selector. To fix this, we ensure methods for the base type are computed, then only do the implicit dot check if we can find a matched method. Fixes #54348 Change-Id: Iefe84ff330830afe35c5daffd499824db108da23 Reviewed-on: https://go-review.googlesource.com/c/go/+/422274 TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Matthew Dempsky <mdempsky@google.com> Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com> Auto-Submit: Keith Randall <khr@golang.org> Reviewed-by: Keith Randall <khr@golang.org>

phemmer mentioned this issue Jun 17, 2022

cmd/compile: Wrong line number on "ambiguous selector" message #53420

Closed

thanm added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jun 17, 2022

griesemer added this to the Go1.20 milestone Jun 17, 2022

griesemer added the NeedsFix The path to resolution is known, but the work has not been done. label Jun 17, 2022

gopherbot removed the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jun 17, 2022

griesemer added the generics Issue is related to generics label Jun 17, 2022

griesemer assigned mdempsky and griesemer Jun 17, 2022

gopherbot closed this as completed in 1243ec9 Jul 6, 2022

gopherbot mentioned this issue Jul 6, 2022

cmd/compile: ambiguous selector with generic interface & embedded types [1.18 backport] #53723

Closed

dmitshur modified the milestones: Go1.20, Go1.19 Jul 12, 2022

phemmer mentioned this issue Jul 28, 2022

cmd/test: Generic not declared by package when testing with GOEXPERIMENT=unified #54112

Closed

golang locked and limited conversation to collaborators Aug 9, 2023

gopherbot added the FrozenDueToAge label Aug 9, 2023

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cmd/compile: ambiguous selector with generic interface & embedded types #53419

cmd/compile: ambiguous selector with generic interface & embedded types #53419

phemmer commented Jun 17, 2022

thanm commented Jun 17, 2022

griesemer commented Jun 17, 2022

mdempsky commented Jun 17, 2022

griesemer commented Jun 17, 2022

gopherbot commented Jun 17, 2022

gopherbot commented Jun 24, 2022

gopherbot commented Jun 28, 2022

cuonglm commented Jun 28, 2022

griesemer commented Jul 1, 2022

randall77 commented Jul 6, 2022

gopherbot commented Jul 6, 2022

gopherbot commented Aug 9, 2022

cmd/compile: ambiguous selector with generic interface & embedded types #53419

cmd/compile: ambiguous selector with generic interface & embedded types #53419

Comments

phemmer commented Jun 17, 2022

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

Does this issue reproduce with the latest release?

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

What did you do?

What did you expect to see?

What did you see instead?

thanm commented Jun 17, 2022

griesemer commented Jun 17, 2022

mdempsky commented Jun 17, 2022

griesemer commented Jun 17, 2022

gopherbot commented Jun 17, 2022

gopherbot commented Jun 24, 2022

gopherbot commented Jun 28, 2022

cuonglm commented Jun 28, 2022

griesemer commented Jul 1, 2022

randall77 commented Jul 6, 2022

gopherbot commented Jul 6, 2022

gopherbot commented Aug 9, 2022

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

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