cmd/gofmt: comments in expr-stmt are not arranged

[hirochachacha]

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)?
   go version go1.6 darwin/amd

2. What operating system and processor architecture are you using (go env)?
   GOARCH="amd64"
   GOBIN=""
   GOEXE=""
   GOHOSTARCH="amd64"
   GOHOSTOS="darwin"
   GOOS="darwin"
   GOPATH="/Users/hiro/.go"
   GORACE=""
   GOROOT="/Users/hiro/go1.6"
   GOTOOLDIR="/Users/hiro/go1.6/pkg/tool/darwin_amd64"
   GO15VENDOREXPERIMENT="1"
   CC="clang"
   GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fno-common"
   CXX="clang++"
   CGO_ENABLED="1"

3. What did you do?
   I was trying to preallocate buffer for encoding.
   After I ran gofmt, I expected comments in expr-stmt are arranged, but not.

   package main
   
   func main() {
       var val []byte
       var name string
   
       buf := make([]byte, 24+ // min buffer size
           4+len(val)+ // tagLen + value
           2+len(name)+1+ // nameLen + name + '\0'
           16) // checksum
   
       _ = buf
   }

   https://play.golang.org/p/wAVUh_sGmw

4. What did you expect to see?

   package main
   
   func main() {
       var val []byte
       var name string
   
       buf := make([]byte, 24+ // min buffer size
           4+len(val)+         // tagLen + value
           2+len(name)+1+      // nameLen + name + '\0'
           16)                 // checksum
   
       _ = buf
   }

5. What did you see instead?
   same as input.

[griesemer]

Agreed that the expected output is much nicer. We should try to fix this at some point.