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cmd/compile: report variable declared but not used when only a field of a struct-typed variable is written to #50778

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qiangli opened this issue Jan 24, 2022 · 4 comments
Closed

cmd/compile: report variable declared but not used when only a field of a struct-typed variable is written to #50778

qiangli opened this issue Jan 24, 2022 · 4 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@qiangli
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qiangli commented Jan 24, 2022

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

$ go version

go version go1.16.7 darwin/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

GO111MODULE=""

GOARCH="amd64"

GOBIN=""

GOCACHE="/Users/user/Library/Caches/go-build"

GOENV="/Users/user/Library/Application Support/go/env"

GOEXE=""

GOEXPERIMENT=""

GOFLAGS=""

GOHOSTARCH="amd64"

GOHOSTOS="darwin"

GOINSECURE=""

GOMODCACHE="/Users/user/go/pkg/mod"

GONOPROXY="github.com/myurl/"

GONOSUMDB="github.com/myurl/"

GOOS="darwin"

GOPATH="/Users/user/go"

GOPRIVATE="github.com/myurl/*"

GOPROXY="https://proxy.golang.org,direct"

GOROOT="/Users/user/go"

GOSUMDB="sum.golang.org"

GOTMPDIR=""

GOTOOLDIR="/Users/user/go/pkg/tool/darwin_amd64"

GOVCS=""

GOVERSION="go1.17.6"

GCCGO="gccgo"

AR="ar"

CC="clang"

CXX="clang++"

CGO_ENABLED="1"

GOMOD="/Users/user/bug/go.mod"

CGO_CFLAGS="-g -O2"

CGO_CPPFLAGS=""

CGO_CXXFLAGS="-g -O2"

CGO_FFLAGS="-g -O2"

CGO_LDFLAGS="-g -O2"

PKG_CONFIG="pkg-config"

GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/2r/7l5dccss0y74mcl41nqbpyfm6h04p

What did you do?

It is desired that an error be reported when running go vet/build with the following code:

package main

import (
	"net/url"
)

func main() {
	s := "https://example.com"
	myUrl, err := url.Parse(s)
	if err != nil {
		panic(err)
	}
        // myUrl is used but not really.
	myUrl.Scheme = "http"
}

What did you expect to see?

myUrl declared but not used

What did you see instead?

No error.
@mknyszek mknyszek changed the title Not able to detect "variable declared but not used" cmd/compile: report variable declared but not used when only a field of a struct-typed variable is written to Jan 24, 2022
@mknyszek mknyszek added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jan 24, 2022
@mknyszek mknyszek added this to the Backlog milestone Jan 24, 2022
@seankhliao
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Duplicate of #449

@seankhliao seankhliao marked this as a duplicate of #449 Jan 24, 2022
@mknyszek
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I don't think that this is going to be possible to add now because it'll cause programs that previously compiled to no longer compile which breaks the Go 1 backwards compatibility promise.

@mknyszek
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@seankhliao Good catch!

@mknyszek
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And yes, as the other bug says, a vet check is reasonable and won't break backwards compatibility.

@golang golang locked and limited conversation to collaborators Jan 24, 2023
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