Go race detector false positive due to shadowed variable

[tiborvass]

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

$ go version
go version go1.21.0 darwin/arm64

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='arm64'
GOBIN=''
GOCACHE='/Users/tibor/Library/Caches/go-build'
GOENV='/Users/tibor/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/tibor/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/tibor/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.21.0'
GCCGO='gccgo'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/2y/mtr77k3n3_d_xqpqs9j26gb40000gn/T/go-build2848548716=/tmp/go-build -gno-record-gcc-switches -fno-common'
uname -v: Darwin Kernel Version 22.5.0: Thu Jun  8 22:21:34 PDT 2023; root:xnu-8796.121.3~7/RELEASE_ARM64_T8112
ProductName:		macOS
ProductVersion:		13.4.1
ProductVersionExtra:	(c)
BuildVersion:		22F770820d
lldb --version: lldb-1403.0.17.67
Apple Swift version 5.8.1 (swiftlang-5.8.0.124.5 clang-1403.0.22.11.100)

What did you do?

$ cat repro.go
package main

import (
	"context"
)

func f(ctx context.Context) (context.Context, error) {
	return ctx, nil
}

func main() {
	ctx := context.Background()
	go func() {
		_ = ctx
	}()
	ctx, err := f(ctx)
	_ = err
	_ = ctx
}
$ go run -race repro.go

What did you expect to see?

exit code 0

What did you see instead?

==================
WARNING: DATA RACE
Read at 0x00c0001160c0 by goroutine 5:
  main.main.func1()
      repro.go:14 +0x2c

Previous write at 0x00c0001160c0 by main goroutine:
  main.main()
      repro.go:16 +0x114

Goroutine 5 (running) created at:
  main.main()
      repro.go:13 +0xf4
==================
Found 1 data race(s)
exit status 66

[seankhliao]

that's a true positive, ctx, err := doesn't create a new ctx