proposal: cmd/vet: detect values assigned but not used

[rmanansa]

Please answer these questions before submitting your issue. Thanks!

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

go1.9 darwin/amd64

Does this issue reproduce with the latest release?

yes

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"

on MacOS X Sierra

What did you do?

I wrote this code below and then run go vet. err is never used or checked.

	defer resp.Body.Close()
	body, err := ioutil.ReadAll(resp.Body)

	return body, resp.StatusCode, nil
}

What did you expect to see?

I expect that when I run $> go vet then I should see some error
notification that this err variable is not used or something.

What did you see instead?

None.

[bradfitz]

Please show complete code.

Is that a new err variable or an existing err? Maybe only body is new in that snippet. If so, that's a different feature request.

[rmanansa]

func (tc *RTClient) requestDo(req *http.Request, auth bool) ([]byte, int, error) {
	if auth {
		tokenBasic, err := tc.getToken()
		if err != nil {
			return nil, ExitCode, err
		}
		req.Header.Set(Authorization, Basic+" "+tokenBasic)
	}

	resp, err := tc.httpClient.Do(req)
	if err != nil {
		return nil, ExitCode, err
	}

	defer resp.Body.Close()
	body, err := ioutil.ReadAll(resp.Body)

	return body, resp.StatusCode, nil
}

[rmanansa]

Hello @bradfitz thanks for the quick reply. The second to the last line of the function has err redeclared. Was expecting that running go vet will flag it when there are no usage of err var after it got redeclared.

[bradfitz]

The err variable isn't redeclared there. Only body is declared. The err variable is just reassigned.

That is, your bug report or feature request is equivalent to:

package vettest

func foo() {
        a := 1
        if a == 2 {
                // ...
        }
        a = 3 // no vet warning here                                                                                                                                              
}               

[dominikh]

FTR, staticcheck as well as ineffassign catch this.