flag: compiler not picking up on redefined flags

[udf2457]

Go version

go version go1.22.3 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOOS='darwin'
GOPROXY='direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.22.3'
GCCGO='gccgo'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'

What did you do?

package main

import (
	"flag"
	"fmt"
)

func main() {
	a := flag.String("a", "", "")
	b := flag.String("a", "", "")
	fmt.Println(a)
	fmt.Println(b)
	flag.Parse()
}

What did you see happen?

go build returns no error

What did you expect to see?

Warning about flag redefined

[randall77]

go build does not return an error in this case. Running the program will (a panic).
It is possible vet or some other analysis tool could detect this and report it. But it's probably pretty rare, and is easily detected at runtime, so it is not clear it would qualify for inclusion.

[udf2457]

is easily detected at runtime

With all due respect, that's a lazy argument.

It makes the developer look sloppy if you ship out code with errors that could and, frankly, should have been prevented by vet or other linting.

[randall77]

It also makes the developer look sloppy if they don't test their binary at all before shipping it.

Assuming your flag.String calls are at the start of the main function, you literally can't run the binary at all, it will immediately fail.

[udf2457]

Testing code is not for the purpose of finding stupid things a linter should have picked up.