context: valueCtx's String panics if value is nil

[tchung1118]

Go version

go version go1.23rc1 X:nocoverageredesign linux/amd64

Output of go env in your module/workspace:

GO111MODULE='off'
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/user/.cache/go-build'
GOENV='/home/user/.config/go/env'
GOEXE=''
GOEXPERIMENT='nocoverageredesign'
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/user/go-code2/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/user/go-code2'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/user/.cache/bazel/_bazel_taiwon/a4cfce9b81ac8aa474cbfb97d6c4bc91/external/go_sdk'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/user/.cache/bazel/_bazel_taiwon/a4cfce9b81ac8aa474cbfb97d6c4bc91/external/go_sdk/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.23rc1 X:nocoverageredesign'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/user/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD=''
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 -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build4074946335=/tmp/go-build -gno-record-gcc-switches'

What did you do?

Created a context via calling context.WithValue and passed nil to the value and tried printing:

ctx := context.WithValue(context.Background(), contextKey{}, nil)
fmt.Printf("%v\n", ctx)

Playground:
https://go.dev/play/p/vtF3t_JWxIC?v=gotip

What did you see happen?

Printed the following:

%!v(PANIC=String method: runtime error: invalid memory address or nil pointer dereference)

What did you expect to see?

In 1.22, the above program prints:

context.Background.WithValue(type main.contextKey, val <not Stringer>)

[gabyhelp]

Related Issues and Documentation

• context: panic when creating an invalid context #37908 (closed)
• ValueContext ctx.Value() panic #58846 (closed)
• context: Breaking change in Go 1.15 not called out in the release notes #40737 (closed)
• context: should panic at WithValue but not #54708 (closed)
• cmd/vet: warn when return value of context.WithValue is lost #41149 (closed)
• valueCtx call Value can cause panic #41254 (closed)
• net/http: Request.WithContext now panics if URL is nil #20601 (closed)
• affected/package: os/exec panic with CommandContext #58828 (closed)

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[gopherbot]

Change https://go.dev/cl/597415 mentions this issue: context: handle nil values for valueCtx.String()