cmd/go: newlines inconsistently preserved in go.mod rewriting

[zx2c4]

I'm seeing this in 1.13beta1.

Phase 1: Make a go.mod file:

$ cat > go.mod <<_EOF
module golang.zx2c4.com/wireguard/windows

require (
        golang.zx2c4.com/wireguard master

        golang.org/x/crypto latest
        golang.org/x/net latest
        golang.org/x/sys latest
        golang.org/x/text latest

        github.com/lxn/walk latest
        github.com/lxn/win latest
)

replace (
        github.com/lxn/walk => golang.zx2c4.com/wireguard/windows pkg/walk
        github.com/lxn/win => golang.zx2c4.com/wireguard/windows pkg/walk-win
)

Phase 2: Resolve everything in it using go get:

$ GOPROXY=direct go get
go: finding golang.zx2c4.com/wireguard master
go: finding golang.org/x/crypto latest
go: finding golang.org/x/net latest
go: finding golang.org/x/sys latest
go: finding github.com/lxn/walk latest
go: finding github.com/lxn/win latest
go: finding golang.zx2c4.com/wireguard/windows pkg/walk
go: finding golang.zx2c4.com/wireguard/windows pkg/walk-win
$ cat go.mod
module golang.zx2c4.com/wireguard/windows

require (

        github.com/lxn/walk v0.0.0-20190619151032-86d8802c197a
        github.com/lxn/win v0.0.0-20190716185335-d1d36f0e4f48

        golang.org/x/crypto v0.0.0-20190820162420-60c769a6c586
        golang.org/x/net v0.0.0-20190813141303-74dc4d7220e7
        golang.org/x/sys v0.0.0-20190813064441-fde4db37ae7a
        golang.org/x/text v0.3.2
        golang.zx2c4.com/wireguard v0.0.20190806-0.20190822065259-3cedc22d7b49
)

replace (
        github.com/lxn/walk => golang.zx2c4.com/wireguard/windows v0.0.0-20190805140616-31a1b114e4f4
        github.com/lxn/win => golang.zx2c4.com/wireguard/windows v0.0.0-20190716185335-d1d36f0e4f48
)

go 1.13

Phase 3: Build it:

$ go build
...
$ cat go.mod
module golang.zx2c4.com/wireguard/windows

require (
        github.com/lxn/walk v0.0.0-20190619151032-86d8802c197a
        github.com/lxn/win v0.0.0-20190716185335-d1d36f0e4f48

        golang.org/x/crypto v0.0.0-20190820162420-60c769a6c586
        golang.org/x/net v0.0.0-20190813141303-74dc4d7220e7
        golang.org/x/sys v0.0.0-20190813064441-fde4db37ae7a
        golang.org/x/text v0.3.2
        golang.zx2c4.com/wireguard v0.0.20190806-0.20190822065259-3cedc22d7b49
)

replace (
        github.com/lxn/walk => golang.zx2c4.com/wireguard/windows v0.0.0-20190805140616-31a1b114e4f4
        github.com/lxn/win => golang.zx2c4.com/wireguard/windows v0.0.0-20190716185335-d1d36f0e4f48
)

go 1.13

---

Notice how between Phase 2 and Phase 3, a new line after require ( is added and then removed?

Phase 2:

require (

        github.com/lxn/walk v0.0.0-20190619151032-86d8802c197a

Phase 3:

require (
        github.com/lxn/walk v0.0.0-20190619151032-86d8802c197a

[bcmills]

Resolve everything in it using go get:

Note that go get is equivalent to go get .: it fetches and builds the package in the current directory, not everything in the go.mod file. (Still shouldn't be adding spurious newlines, though.)

[karuppiah7890]

I'm willing to fix this issue. I'll check it out and ping here if I need help 😄

[karuppiah7890]

@zx2c4 I'm not able to reproduce the issue. I get an error instead. I'm not using the beta version though, I'm using the latest master branch commit 66ff373

$ go version
go version devel +66ff373911 Sat Aug 24 01:11:56 2019 +0000 darwin/amd64

This is the go.mod file

$ cat go.mod
module golang.zx2c4.com/wireguard/windows

require (
        golang.zx2c4.com/wireguard master

        golang.org/x/crypto latest
        golang.org/x/net latest
        golang.org/x/sys latest
        golang.org/x/text latest

        github.com/lxn/walk latest
        github.com/lxn/win latest
)

replace (
        github.com/lxn/walk => golang.zx2c4.com/wireguard/windows pkg/walk
        github.com/lxn/win => golang.zx2c4.com/wireguard/windows pkg/walk-win
)

on executing:

$ go get -v
go: finding golang.zx2c4.com/wireguard master
go: finding golang.org/x/crypto latest
go: finding golang.org/x/net latest
go: finding golang.org/x/sys latest
go: finding github.com/lxn/walk latest
go: finding github.com/lxn/win latest
go: finding golang.zx2c4.com/wireguard/windows pkg/walk
go: finding golang.zx2c4.com/wireguard/windows pkg/walk-win
go: errors parsing go.mod:
/Users/karuppiahoss/oss/github.com/karuppiah7890/go-issues/33779/go.mod:16: replace golang.zx2c4.com/wireguard/wind
ows: version "pkg/walk" invalid: version "pkg/walk" invalid: disallowed version string
/Users/karuppiahoss/oss/github.com/karuppiah7890/go-issues/33779/go.mod:17: replace golang.zx2c4.com/wireguard/wind
ows: version "pkg/walk-win" invalid: version "pkg/walk-win" invalid: disallowed version string

[zx2c4]

export GOPROXY=direct

[karuppiah7890]

Thanks @zx2c4 😄 I'm able to reproduce the issue!

[karuppiah7890]

I haven't proceeded much with this issue. Me and my friend @aswinkarthik worked on this. We tried to debug it, but couldn't do much. If someone would help us on how to debug golang code using a debugger , it would be great. We use Intellij IDEA and VSCode too. We'll try more from our side too.

The one we noticed was, the new line comes due to the rearranging of the new line that was put by the user. We didn't know where to get rid of it and how it came as manually putting println and compiling and running didn't help much with debugging

[gopherbot]

Change https://golang.org/cl/199917 mentions this issue: cmd/go/internal/modfile: do not print a newline for empty comment lines

[zx2c4]

Actually what's happening here is that the module list is being sorted, but the empty line above them in the original file is considered to be a "comment" line, which has an association with the non-comment line below it, and this association is preserved. It probably doesn't make sense to persist blank comment lines during sorting. I'll fix this up.