Add linter wastedassign

[sanposhiho]

closes #1492

Hi :D

Add wastedassign

wastedassign finds wasted assignment statements

found the value ...

• reassigned, but never used afterward
• reassigned, but reassigned without using the value

func f() int {
	a := 0 
        b := 0
        fmt.Print(a)
        fmt.Print(b)
        a = 1  // This reassignment is wasted, because never used afterwards. Wastedassign find this 

        b = 1  // This reassignment is wasted, because reassigned without use this value. Wastedassign find this 
        b = 2
        fmt.Print(b)
        
	return 1 + 2
}

[boring-cyborg]

Hey, thank you for opening your first Pull Request !

[CLAassistant]

All committers have signed the CLA.

[ldez]

Hello @sanposhiho,

could you explain why you created a fork of golang.org/x/tools (https://github.com/sanposhiho/tools) ?

I see your change:

https://github.com/sanposhiho/tools/blob/da3530a453b58298252f9d97b5419d0fc231f00b/go/analysis/passes/buildssa/buildssa.go#L51

mode := ssa.BuilderMode(ssa.NaiveForm)

https://github.com/golang/tools/blob/e0d201561e39aeaab8136532f2bbe17ae1ef24ff/go/analysis/passes/buildssa/buildssa.go#L49-L51

	// Some Analyzers may need GlobalDebug, in which case we'll have
	// to set it globally, but let's wait till we need it.
	mode := ssa.BuilderMode(0)

It seems, when I read the comment, that a PR on that point on the repo https://github.com/golang/tools will be welcome.

I pay attention to this point because it can impact golangci-lint's performance because this lib is at the heart of golangci-lint's performance optimizations.

[sanposhiho]

Hi @ldez!

could you explain why you created a fork of golang.org/x/tools

I use the mode ssa.NaiveForm, because without this mode, the process called "lifting" replaces some store process with ssa.Value and can't track the use of variables.

It seems, when I read the comment, that a PR on that point on the repo https://github.com/golang/tools will be welcome.
I pay attention to this point because it can impact golangci-lint's performance because this lib is at the heart of golangci-lint's performance optimizations.

OK, I'll create PR on https://github.com/golang/tools

[sanposhiho]

Hi team.
I'm sorry it took me so long to reply.

I removed the dependency of wastedassign on sanposhiho/tools, because it seemed to take a while for the proposal to go/tools to be supported.

I pay attention to this point because it can impact golangci-lint's performance because this lib is at the heart of golangci-lint's performance optimizations.

So, This concern has been addressed now.

[SVilgelm]

it would be great if you can use golang.org/x/tools v0.1.0 instead of v0.0.0-20200918232735-d647fc253266, just to be consistent with golangci-lint

[ldez]

Could you replace the panic by errors?

https://github.com/sanposhiho/wastedassign/blob/master/wastedassign.go#L75
https://github.com/sanposhiho/wastedassign/blob/master/wastedassign.go#L80

[sanposhiho]

@ldez @SVilgelm
Thanks for reviews, fixed them

[SVilgelm]

Looks good to me. Thank you

[ldez]

LGTM

[golangci-automator]

Hey, @sanposhiho — we just merged your PR to golangci-lint! 🔥🚀

golangci-lint is built by awesome people like you. Let us say “thanks”: we just invited you to join the GolangCI organization on GitHub.
This will add you to our team of maintainers. Accept the invite by visiting this link.

By joining the team, you’ll be able to label issues, review pull requests, and merge approved pull requests.
More information about contributing is here.

Thanks again!