x/tools/cmd/goimports: inserts unexpected blank space after an inline comment

[ncw]

What version of Go are you using (go version)?

go version go1.10.1 linux/amd64

with

goimports latest 16f8f9b

Does this issue reproduce with the latest release?

Yes with the latest version of goimports

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/ncw/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/ncw/go"
GORACE=""
GOROOT="/opt/go/go1.10"
GOTMPDIR=""
GOTOOLDIR="/opt/go/go1.10/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build952400509=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I saved this program into a file https://play.golang.org/p/soaLshUrvTf

package main

import (
	"fmt"
	"os"

	"github.com/ncw/rclone/vfs/vfsflags"
	"github.com/spf13/cobra"
	"golang.org/x/net/context" // switch to "context" when we stop supporting go1.8
	"golang.org/x/net/webdav"
)

func main() {
	var (
		_ context.Context
		_ *os.File
		_ webdav.File
		_ cobra.Command
		_ = vfsflags.Opt
	)
	fmt.Println("Hello")
}

I then ran goimports -d on it

What did you expect to see?

I expected to see no output

What did you see instead?

I saw that goimports wanted to add an extra blank line in.

diff -u goimportstest.go.orig goimportstest.go
--- goimportstest.go.orig	2018-07-06 09:19:48.722405604 +0100
+++ goimportstest.go	2018-07-06 09:19:48.722405604 +0100
@@ -7,6 +7,7 @@
 	"github.com/ncw/rclone/vfs/vfsflags"
 	"github.com/spf13/cobra"
 	"golang.org/x/net/context" // switch to "context" when we stop supporting go1.8
+
 	"golang.org/x/net/webdav"
 )
 

Discussion

goimports didn't used to add this blank line in, so I used git bisect to discover where the behaviour changed, and I discovered it was introduced in b23eb62 by @Gnouc as part of fixing #23709

I haven't worked out the exact situation that causes the problem - it seems quite sensitive to exactly which import lines are present. For example if you remove the vfsflags import then it doesn't insert that extra blank line. If you remove the comment // switch to ... then it doesn't exhibit the problem.

[mvdan]

Comments are tricky to handle, so I wouldn't be surprised if some edge case was mishandled in the fix above.

[fraenkel]

This new behavior was introduced by imports: fixup comments on import lines correctly

[gopherbot]

Change https://golang.org/cl/122538 mentions this issue: imports: fix fixup comment insert extra blank line

[cuonglm]

@ncw I push a fix for that case, would you mind checking?

[ncw]

@fraenkel that fixes the issue I posted but not this one

package main

import (
	"encoding/json"
	"io"
	"net/http"
	_ "net/http/pprof" // install the pprof http handlers
	"strings"

	"github.com/pkg/errors"
)

func main() {
	_ = strings.ToUpper("hello")
	_ = io.EOF
	var (
		_ json.Number
		_ *http.Request
		_ errors.Frame
	)
}

diff -u Go/goimportstest2.go.orig Go/goimportstest2.go
--- Go/goimportstest2.go.orig	2018-07-09 09:53:26.451454978 +0100
+++ Go/goimportstest2.go	2018-07-09 09:53:26.451454978 +0100
@@ -5,6 +5,7 @@
 	"io"
 	"net/http"
 	_ "net/http/pprof" // install the pprof http handlers
+
 	"strings"
 
 	"github.com/pkg/errors"

[cuonglm]

@ncw should ok now.

[ncw]

@Gnouc That fixes all my test cases :-) I also tried it on a larger corpus of go files and that looks fine too -so looked fixed to me :-)