cmd/vet: shadowed variables check doesn't catch shadowing from short assignment in if statements

[stevekuznetsov]

For the following example:

package main

import (
    "encoding/json"
    "io/ioutil"
    "log"
    "os"
)

func main() {
    if len(os.Args) != 2 {
        log.Fatal("Usage: jsonformat.go <filename>")
    }

    byt, err := ioutil.ReadFile(os.Args[1])
    if err != nil {
        log.Fatalf("ERROR: Unable to read file %q: %v\n", os.Args[1], err)
    }

    var dat map[string]interface{}

    if err := json.Unmarshal(byt, &dat); err != nil { // this err is not flagged as masking the err in the outer scope, incorrectly
        log.Fatalf("ERROR: Invalid JSON file  '%v': %v\n", os.Args[1], err)
    }

    if output, err := json.MarshalIndent(dat, "", "  "); err != nil { // this err is flagged as masking the err in the outer scope, correctly
        log.Fatalf("ERROR: Unable to indent JSON file: %v\n", os.Args[1])
    } else {
        os.Stdout.Write(append(output, '\n'))
    }
}

One the errors is not flagged correctly, even when using -shadowstrict. My version of go tool vet is at 108746816ddf01ad0c2dbea08a1baef08bc47313

[stevekuznetsov]

Original discussion: https://groups.google.com/forum/#!topic/golang-nuts/uD0wsdeQ-xs

[ianlancetaylor]

This is fixed in Go 1.6, though I do not know what fixed it.

[stevekuznetsov]

I updated my version of go vet with a go get -u golang.org/x/tool/cmd/vet today... Should that not have picked up this change?

[kostya-sh]

I believe this was fixed by 3c1712d

@stevekuznetsov, vet is part of Go tool set since Go 1.5. golang.org/x/tool/cmd/vet is no longer maintained.

I think golang.org/x/tool/cmd/vet should be deleted at some point as it creates a lot of confusion.