x/tools/cmd/goimports: support gofmt option to simplify code

[aronatkins]

go version go1.8.3 darwin/amd64

Using goimports as of golang/tools@84a35ef

The goimports command handles import fixing and gofmt code formatting. It does not, however, implement the code simplification option -s.

This means that goimports cannot be used as a drop-in replacement to save-hooks that use gofmt -s (for example, when using -s as the gofmt-args value for the save-hook with go-mode.el).

package main

import "fmt"

type Thing struct {
	value int
}

func main() {
	things := []Thing{
		Thing{value: 42},
	}
	fmt.Printf("things: %+v\n", things)
}

There are no problems identified by goimports:

$ goimports -d complex.go

With gofmt -s, we get:

$ gofmt -s -d complex.go
diff complex.go gofmt/complex.go
--- /var/folders/ts/s940qvdj5vj1czr9qh07fvtw0000gn/T/gofmt822245016	2017-08-16 12:34:31.000000000 -0400
+++ /var/folders/ts/s940qvdj5vj1czr9qh07fvtw0000gn/T/gofmt235716375	2017-08-16 12:34:31.000000000 -0400
@@ -8,7 +8,7 @@

 func main() {
 	things := []Thing{
-		Thing{value: 42},
+		{value: 42},
 	}
 	fmt.Printf("things: %+v\n", things)
 }

[griesemer]

FWIW, it's a historical artifact that the simplify (-s) mechanism is implemented as part of the gofmt command. I think AST simplification (and rewriting) should be factored out and provided via separate libraries. Then those libraries could be trivially used from other places (incl. gofmt or goimports if so desired).

[mbyio]

@griesemer So basically, to implement this, someone should first factor out the simplification code and then use that to implement simplification in goimports?

[griesemer]

@mbyio Yes.

[jimeh]

@griesemer isn't the point of goimports that it's a drop-in replacement for gofmt?

[griesemer]

@jimeh goimports already does more than gofmt. I'm just suggesting that simplifications such as this should be factored out into a separate library. Maybe that library is used by gofmt and goimports, or just goimports. But the main point is that the code should be isolated into a separate package.