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cmd/vet: teach vet that putting a large value in an interface makes a copy #14529

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josharian opened this issue Feb 26, 2016 · 6 comments
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cmd/vet: teach vet that putting a large value in an interface makes a copy #14529

josharian opened this issue Feb 26, 2016 · 6 comments
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@josharian
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package main

import "sync"

type T struct {
    sync.Mutex
    _ [4]byte
}

func main() {
    var t T

    var s T
    s = t

    var e interface{}
    e = t
}
$ go vet x.go
x.go:14: assignment copies lock value to s: main.T
exit status 1

vet should also complain about the assignment e = t, since it also copies t's value.
@josharian josharian added this to the Unplanned milestone Feb 26, 2016
@josharian josharian mentioned this issue Feb 26, 2016
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@rogpeppe
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This would have caught some bugs for us.

@josharian
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cc @valyala :)

@valyala
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valyala commented Mar 17, 2016

It looks like this is already fixed in #14664 (go tip):

go vet 1.go
1.go:14: assignment copies lock value to s: main.T
1.go:17: assignment copies lock value to e: main.T

@valyala
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valyala commented Mar 17, 2016

Other cases must be checked such as passing lock as function argument accepting interface{} or returning lock from function returning interface{}

@valyala
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valyala commented Mar 18, 2016

Prepared a CL, which expands copylock check to function calls and return values - see https://go-review.googlesource.com/20832 . This catches passing lock into interface{} in these cases.

@gopherbot
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CL https://golang.org/cl/20832 mentions this issue.

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@rogpeppe @josharian @valyala @gopherbot