unparam does not support build tags

[benpaxton-hf]

unparam currently doesn't support build tags, which means packages which require a non-implicit build tag can't be linted, e.g.:

main.go

package main

import (
	"./sub"
	"fmt"
)

func main() {
	fmt.Printf("Hello, %s!\n", sub.Get())
}

sub/sub_a.go

//+build a

package sub

func Get() string {
	return "world"
}

sub/sub_b.go

//+build b

package sub

func Get() string {
	return "everyone"
}

sub/sub.go

package sub

// some shared code

$ ls
main.go  sub
$ unparam .
.../main.go:9:29: Get not declared by package sub
couldn't load packages due to errors: .
$ go run -tags a main.go 
Hello, world!
$ go run -tags b main.go 
Hello, everyone!

[mvdan]

Good point - this needs to be added.

Ideally, there would be a way to check all tag combinations without having to multiply the amount of work. I have no idea how to do that, though.

[benpaxton-hf]

Checking all tag combinations is probably impossible without knowing what they mean - in my example case, for example, a b and !a !b are not valid - only a !b and !a b are valid tag combinations.

If unparam -tags a . worked, though, it'd be easy to use external tools to enumerate valid tag combinations and lint each, e.g.

lint-unparam:
    unparam -tags a .
    unparam -tags b .

[dmitshur]

In case this is helpful, see https://github.com/mdempsky/unconvert/pull/27/files for an example of how this can be implemented.

[mvdan]

@shurcooL thanks, that just saved me a good ten minutes of furious head-scratching.

[mvdan]

Also, jesus, the help output is bad:

 $ unparam -h
usage: unparam [flags] [package ...]
  -debug
        debug prints
  -exported
        inspect exported functions
  -tags build tags
        a list of build tags to consider satisfied during the build. For more information about build tags, see the description of build constraints in the documentation for the go/build package
  -tests
        include tests (default true)

I've filed golang/go#23464 about this.

[dmitshur]

FYI, according to https://speakerdeck.com/campoy/the-state-of-go-1-dot-10?slide=23, there have been some improvements to the flags package in Go 1.10 to make its output more readable.

Also, friendly ping on resolving this issue. I would've liked to use it today:

$ unparam -tags=dev ./...
flag provided but not defined: -tags

[mvdan]

Thanks for the ping - I got sidetracked on this.