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cmd/vet: warn when return value of context.WithValue is lost #41149

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ancarda opened this issue Aug 31, 2020 · 6 comments
Closed

cmd/vet: warn when return value of context.WithValue is lost #41149

ancarda opened this issue Aug 31, 2020 · 6 comments

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@ancarda
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@ancarda ancarda commented Aug 31, 2020

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

go version go1.14.7 linux/amd64

Does this issue reproduce with the latest release?

Yes.

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

Not Applicable, but anyway...

go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/ancarda/.cache/go-build"
GOENV="/home/ancarda/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/ancarda/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build172081220=/tmp/go-build -gno-record-gcc-switches"

What did you do?

https://play.golang.org/p/NY8BWaciqad

package main

import (
	"context"
	"fmt"
)

func f(ctx context.Context) {
	context.WithValue(ctx, "foo", -6)
}

func main() {
	ctx := context.TODO()
	f(ctx)
	fmt.Println(ctx.Value("foo"))
}

What did you expect to see?

An error indicating that line 9 has a bug; that is, WithContext returns a new context but is not returned. Perhaps something like:

./main.go:9:2: Context.WithValue returns a new instance, which is lost.

What did you see instead?

When I run go vet on this code, I don't get any errors.

@dmitshur dmitshur added this to the Backlog milestone Sep 1, 2020
@dmitshur dmitshur changed the title cmd/vet: Warn when return value of context.WithValue is lost cmd/vet: warn when return value of context.WithValue is lost Sep 1, 2020
@dmitshur
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@dmitshur dmitshur commented Sep 1, 2020

/cc @alandonovan per owners.

It may be relevant that according to this tweet and issue dominikh/go-tools#819, this check is planned to be added to staticcheck.

Also /cc @davecheney @Sajmani @dominikh FYI.

@alandonovan
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@alandonovan alandonovan commented Sep 1, 2020

@ancarda
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@ancarda ancarda commented Sep 1, 2020

Thanks @alandonovan, I've filed a PR here: golang/tools#248 🙂

@gopherbot
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@gopherbot gopherbot commented Sep 1, 2020

Change https://golang.org/cl/252057 mentions this issue: unusedresult.go: Include context.With* functions

@dmitshur dmitshur modified the milestones: Backlog, Go1.16 Sep 1, 2020
@dmitshur
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@dmitshur dmitshur commented Sep 1, 2020

The x/tools commit will need to be vendored into the main repository so that cmd/vet picks it up. See CL 236138 for a past example.

Reopening for that.

@dmitshur dmitshur reopened this Sep 1, 2020
@dmitshur dmitshur added NeedsFix and removed NeedsInvestigation labels Sep 1, 2020
@gopherbot
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@gopherbot gopherbot commented Sep 6, 2020

Change https://golang.org/cl/252941 mentions this issue: cmd: update golang.org/x/tools to v0.0.0-20200901153117-6e59e24738da

@gopherbot gopherbot closed this in b4944ef Sep 9, 2020
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