cmd/compile: gc inconsistent about reporting "unused variable" errors #8560

adonovan · 2014-08-20T18:09:23Z

For this program:
  http://play.golang.org/p/BzMO7Vt3uy
  switch x := interface{}(nil).(type) {}
go/types reports an error but gc does not.

I realize the spec does not say what should happen here, but the fact of this
implementation-specific behaviour is that we have two dialects of Go whose tools reject
each others' programs.

We should probably make the tools consistent one way or another.
I would also argue in favour of removing this hole in the spec.

griesemer · 2014-09-10T20:49:53Z

Comment 1:

gccgo also complains about this as an unused variable:
$ gccgo x.go
x.go:4:9: error: 'x' declared and not used
  switch x := interface{}(nil).(type) {
         ^
The spec makes this an implementation restriction, but go/types and gccgo agree with how
the implementation restriction should be applied in this case. Making this a cmd/gc bug.

Labels changed: added release-none, repo-main.

Status changed to Accepted.

adg · 2014-11-06T04:21:05Z

Comment 2:

This program should generate the error "p declared but not used":
package main
func main() {
        p := true
        func() {
                p = true
        }()
}
If you remove the closure, the compiler raises the error.

gopherbot · 2015-06-05T18:00:30Z

CL https://golang.org/cl/10757 mentions this issue.

… from go/types gc should ideally consider this an error too; see #8560. Change-Id: Ieee71c4ecaff493d7f83e15ba8c8a04ee90a4cf1 Reviewed-on: https://go-review.googlesource.com/10757 Reviewed-by: Robert Griesemer <gri@golang.org>

rsc · 2016-03-07T19:33:50Z

This is in milestone Unplanned. By my assignment should I infer you are requesting we reprioritize it? Normally Unplanned things have no assignee.

alandonovan · 2016-03-07T19:51:36Z

Yes, that's what I meant. (Sorry if that was unclear or seemed passive-aggressive.)

rsc · 2016-03-07T20:03:42Z

OK, reprioritized to Go 1.7, but that's still no guarantee.

gopherbot · 2016-05-28T03:00:16Z

CL https://golang.org/cl/23528 mentions this issue.

This fixes `go test go/types`. https://golang.org/cl/23487/ introduced this code which contains two unused variables (declared and assigned to, but never read). cmd/compile doesn't report the error due open issue #8560 (the variables are assigned to in a closure), but go/types does. The build bot only runs go/types tests in -short mode (which doesn't typecheck the std lib), hence this doesn't show up on the dashboard either. We cannot call b.Fatal and friends in the goroutine. Communicating the error to the invoking function requires a channel or a mutex. Unless the channel/sycnhronized variable is tested in each iteration that follows, the iteration blocks if there's a failure. Testing in each iteration may affect benchmark times. One could use a time-out but that time depends on the underlying system. Panicking seems good enough in this unlikely case; better than hanging or affecting benchmark times. Change-Id: Idce1172da8058e580fa3b3e398825b0eb4316325 Reviewed-on: https://go-review.googlesource.com/23528 Reviewed-by: Ian Lance Taylor <iant@golang.org> Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>

odeke-em · 2016-08-05T08:39:02Z

@adg your report in #8560 (comment) was a bug that was already reported at #3059, in case you are interested in tracking that case.

jim-minter · 2016-09-27T09:07:17Z

Out of interest, are there any known workarounds for the gorename issue #14596 (short of not using closures in this way across a codebase) that can be used to enable use of gorename in codebases such as that before this issue is resolved?

This is revealed by the go/types package, which is stricter than the Go compiler about unused variables. See also: golang/go#8560

This is revealed by the go/types package, which is stricter than the Go compiler about unused variables. See also: golang/go#8560 Kubernetes-commit: e04b91facf180c17557a44e8e462858ea2936301

This is revealed by the go/types package, which is stricter than the Go compiler about unused variables. See also: golang/go#8560

This fixes `go test go/types`. https://golang.org/cl/23487/ introduced this code which contains two unused variables (declared and assigned to, but never read). cmd/compile doesn't report the error due open issue golang#8560 (the variables are assigned to in a closure), but go/types does. The build bot only runs go/types tests in -short mode (which doesn't typecheck the std lib), hence this doesn't show up on the dashboard either. We cannot call b.Fatal and friends in the goroutine. Communicating the error to the invoking function requires a channel or a mutex. Unless the channel/sycnhronized variable is tested in each iteration that follows, the iteration blocks if there's a failure. Testing in each iteration may affect benchmark times. One could use a time-out but that time depends on the underlying system. Panicking seems good enough in this unlikely case; better than hanging or affecting benchmark times. Change-Id: Idce1172da8058e580fa3b3e398825b0eb4316325 Reviewed-on: https://go-review.googlesource.com/23528 Reviewed-by: Ian Lance Taylor <iant@golang.org> Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>

griesemer · 2021-10-28T03:09:29Z

Marked NeedsInvestigation since we need to re-establish the current facts.

griesemer · 2021-11-03T18:10:03Z

The Go 1.18 compiler correctly reports errors in these cases.
Per #49214 we will accept the correct behavior for 1.18 and document it in the release notes.

adonovan added accepted labels Nov 6, 2014

ianlancetaylor mentioned this issue Apr 6, 2015

go/loader: variable use checks should match the go tool's checks, but do not #10354

Closed

glycerine mentioned this issue Apr 6, 2015

go/loader: variable use checks should match gc #10356

Closed

rsc added this to the Unplanned milestone Apr 10, 2015

rsc removed release-none labels Apr 10, 2015

alandonovan mentioned this issue Jun 2, 2015

cmd/compile: report error for ineffectual variable assignments #10989

Closed

rsc changed the title ~~cmd/gc: gc inconsistent about reporting "unused variable" errors~~ cmd/compile: gc inconsistent about reporting "unused variable" errors Jun 8, 2015

alandonovan mentioned this issue Mar 7, 2016

x/tools/cmd/gorename: analysis of variable usage differs from go build #14596

Closed

alandonovan assigned rsc Mar 7, 2016

rsc removed their assignment Mar 7, 2016

rsc modified the milestones: Go1.7, Unplanned Mar 7, 2016

rsc modified the milestones: Go1.8, Go1.7 May 17, 2016

rmmh pushed a commit to rmmh/kubernetes that referenced this issue Feb 27, 2018

Remove unused variables (only assigned to) from test code.

e04b91f

This is revealed by the go/types package, which is stricter than the Go compiler about unused variables. See also: golang/go#8560

jingxu97 pushed a commit to jingxu97/kubernetes that referenced this issue Mar 13, 2018

Remove unused variables (only assigned to) from test code.

5cde217

This is revealed by the go/types package, which is stricter than the Go compiler about unused variables. See also: golang/go#8560

bradfitz modified the milestones: Go1.11, Go1.12 May 18, 2018

gopherbot modified the milestones: Go1.12, Unplanned May 23, 2018

griesemer mentioned this issue May 6, 2021

cmd/compile: -G=3 mode correctly reports all "declared but not used" errors, but old compiler does not #46004

Closed

griesemer modified the milestones: Unplanned, Go1.18 Oct 28, 2021

griesemer self-assigned this Oct 28, 2021

griesemer mentioned this issue Oct 28, 2021

cmd/compile: consistently report "declared but not used" errors - needs release notes #49214

Closed

griesemer closed this as completed Nov 3, 2021

dmitshur added NeedsFix The path to resolution is known, but the work has not been done. and removed NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Dec 14, 2021

rsc unassigned griesemer Jun 23, 2022

golang locked and limited conversation to collaborators Jun 23, 2023

gopherbot added the FrozenDueToAge label Jun 23, 2023

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cmd/compile: gc inconsistent about reporting "unused variable" errors #8560

cmd/compile: gc inconsistent about reporting "unused variable" errors #8560

adonovan commented Aug 20, 2014

griesemer commented Sep 10, 2014

adg commented Nov 6, 2014

gopherbot commented Jun 5, 2015

rsc commented Mar 7, 2016

alandonovan commented Mar 7, 2016

rsc commented Mar 7, 2016

gopherbot commented May 28, 2016

odeke-em commented Aug 5, 2016

jim-minter commented Sep 27, 2016

griesemer commented Oct 28, 2021

griesemer commented Nov 3, 2021

cmd/compile: gc inconsistent about reporting "unused variable" errors #8560

cmd/compile: gc inconsistent about reporting "unused variable" errors #8560

Comments

adonovan commented Aug 20, 2014

griesemer commented Sep 10, 2014

adg commented Nov 6, 2014

gopherbot commented Jun 5, 2015

rsc commented Mar 7, 2016

alandonovan commented Mar 7, 2016

rsc commented Mar 7, 2016

gopherbot commented May 28, 2016

odeke-em commented Aug 5, 2016

jim-minter commented Sep 27, 2016

griesemer commented Oct 28, 2021

griesemer commented Nov 3, 2021