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cmd/compile: spurious "goto label jumps over declaration" #8042

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dvyukov opened this issue May 20, 2014 · 18 comments
Closed

cmd/compile: spurious "goto label jumps over declaration" #8042

dvyukov opened this issue May 20, 2014 · 18 comments
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Go1.9

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@dvyukov
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dvyukov commented May 20, 2014 

go version devel +4a839bf01b58 Tue May 20 15:52:08 2014 +1000 + linux/amd64

The program is:
package main
func main() {
    goto label
    type X int
    label:
}

$ go build goto.go
goto.go:3: goto label jumps over declaration of X at goto.go:4

The spec only requires new variables to not come into scope:
"Executing the "goto" statement must not cause any variables to come into
scope that were not already in scope at the point of the goto".
@dvyukov
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dvyukov commented May 20, 2014

Comment 1:

Labels changed: added repo-main.

@rsc
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rsc commented May 20, 2014

Comment 2:

Labels changed: added release-go1.4.

Status changed to Accepted.

@rsc
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rsc commented Sep 15, 2014

Comment 3:

Labels changed: added release-go1.5, removed release-go1.4.

@bradfitz bradfitz modified the milestone: Go1.5 Dec 16, 2014
@rsc rsc removed accepted labels Apr 14, 2015
@DanielMorsing
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Fix at https://go-review.googlesource.com/#/c/9442/

@gopherbot
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CL https://golang.org/cl/9442 mentions this issue.

@bradfitz bradfitz reopened this May 15, 2015
@bradfitz
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I reverted the fix, since it broke all the builds.

@rsc rsc changed the title cmd/gc: spurious "goto label jumps over declaration" cmd/compile: spurious "goto label jumps over declaration" Jun 8, 2015
@rsc
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rsc commented Jun 29, 2015

Too late for Go 1.5.

@rsc rsc modified the milestones: Unplanned, Go1.5 Jun 29, 2015
@brentp brentp mentioned this issue Apr 19, 2016
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@ALTree ALTree mentioned this issue Jan 9, 2017
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@ALTree ALTree mentioned this issue Feb 15, 2017
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@ALTree ALTree modified the milestones: Go1.9, Unplanned Feb 15, 2017
@ghost
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ghost commented Feb 22, 2017

At the risk of sounding like a fool: suppose that the next line in main in dvyukov's example is

var v X = 0

What then? I think this is a problem with the spec, and not the toolchain.

@griesemer
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@IronGopher If the declaration were about a variable X rather than a type, then it would be a correct error. The issue is that it's only an error if variables are coming into scope, not types or constants. The spec is clear. This is a compiler bug.

@griesemer griesemer self-assigned this Apr 18, 2017
@djadala
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djadala commented Oct 2, 2017

CC @griesemer @dvyukov
If i modify original program as:

package main
func main() {
    goto label
    X := 0
    label:
}

output is still:

go build t.go
# command-line-arguments
./t.go:3:10: goto label jumps over declaration of X at ./t.go:4:7

go version
go version go1.9 linux/amd64

Should new bug be opened ?

@dvyukov
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dvyukov commented Oct 2, 2017 •
edited

@djadala

Should new bug be opened ?

yes

@djadala
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djadala commented Oct 2, 2017

s/ type X int/ X := 0/

@odeke-em
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odeke-em commented Oct 2, 2017

Never mind my last comment, your bug still stands even on the latest code @djadala :)

@djadala djadala mentioned this issue Oct 2, 2017
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@djadala
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djadala commented Oct 2, 2017

ok, new issue is #22101

@odeke-em
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odeke-em commented Oct 2, 2017 •
edited

Okay hold up though, your program isn't correct and you have made a new variable declaration with

goto L
X := 0

A goto shouldn't allow a variable that wasn't already in scope to come into scope. I don't see the bug here.

@odeke-em
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odeke-em commented Oct 2, 2017

@djadala I've commented on the other issue that this isn't a bug, and coincidentally the spec provides a similar example to what you posted
https://golang.org/ref/spec#GotoStmt

Initially I had copied and pasted the original code without checking it, but on a closer look I deduced that this isn't a bug.

@djadala
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djadala commented Oct 2, 2017

Sorry for noise,
i thought if variable is not used after label, this must compile, but i'm wrong.

@odeke-em
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odeke-em commented Oct 2, 2017

Not a problem at all @djadala, thank you for checking up on the bug.

@golang golang locked and limited conversation to collaborators Oct 2, 2018
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@bradfitz @rsc @DanielMorsing @dvyukov @ALTree @odeke-em @griesemer @gopherbot @djadala