staticcheck: flag recursive closure that never gets used

[seiyab]

• The output of 'staticcheck -version'

staticcheck 2023.1.7 (v0.4.7)

• The output of 'staticcheck -debug.version' (it is fine if this command fails)

staticcheck 2023.1.7 (v0.4.7)

Compiled with Go version: go1.21.1
Main module:
        honnef.co/go/tools@v0.4.7 (sum: h1:9MDAWxMoSnB6QoSqiVr7P5mtkT9pOc1kSxchzPCnqJs=)
Dependencies:
        github.com/BurntSushi/toml@v1.2.1 (sum: h1:9F2/+DoOYIOksmaJFPw1tGFy1eDnIJXg+UHjuD8lTak=)
        golang.org/x/exp/typeparams@v0.0.0-20221208152030-732eee02a75a (sum: h1:Jw5wfR+h9mnIYH+OtGT2im5wV1YGGDora5vTv/aa5bE=)
        golang.org/x/mod@v0.12.0 (sum: h1:rmsUpXtvNzj340zd98LZ4KntptpfRHwpFOHG188oHXc=)
        golang.org/x/sys@v0.11.0 (sum: h1:eG7RXZHdqOJ1i+0lgLgCpSXAp6M3LYlAo6osgSi0xOM=)
        golang.org/x/tools@v0.12.1-0.20230825192346-2191a27a6dc5 (sum: h1:Vk4mysSz+GqQK2eqgWbo4zEO89wkeAjJiFIr9bpqa8k=)

• The output of 'go version'

go version go1.21.1 darwin/arm64

• The output of 'go env'

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/seiya/Library/Caches/go-build'
GOENV='/Users/seiya/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/seiya/.asdf/installs/golang/1.21.1/packages/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/seiya/.asdf/installs/golang/1.21.1/packages'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/seiya/.asdf/installs/golang/1.21.1/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/seiya/.asdf/installs/golang/1.21.1/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.21.1'
GCCGO='gccgo'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/Users/seiya/Projects/repro/staticcheck-fixture/go.mod'
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/wb/yt882gm52pzdsz3_vcvbp_f80000gn/T/go-build869543369=/tmp/go-build -gno-record-gcc-switches -fno-common'

• Exactly which command you ran

staticcheck ./

• Output of the command and what's wrong with the output

main.go:13:6: func fn2 is unused (U1000)

(fn1 should also be detected)

• Where we can read the code you're running Staticcheck on

package main

func main() {
	var fn1 func(int)
	fn1 = func(i int) {
		if i < 0 {
			return
		}
		fn1(i-1)
	}
}

func fn2(i int) {
	if i < 0 {
		return
	}
	fn2(i-1)
}

[dominikh]

I'm afraid this is outside of unused's domain.Syntactically, fn1 is used. We could check for this in some other check, though.