cmd/go: go mod edit -fmt can result in lost comments

[0xmohit]

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

$ go version
go version go1.13beta1 linux/amd64

Does this issue reproduce with the latest release?

Yes, happens with 1.12.6 too. Not tried with tip.

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/mohit/.cache/go-build"
GOENV="/home/mohit/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/mohit/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go-1.13beta1"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go-1.13beta1/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/tmp/exp/go.mod"
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-build485779267=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Executed go mod edit -fmt on the following. (The following is a minimal reproducible example of the actual go.mod file.)

module exp

go 1.13

require (
	foo v0.0.0-00010101000000-000000000000
	// bar v0.0.0-00010101000000-000000000000
)

What did you expect to see?

Perhaps no change.

What did you see instead?

The commented disappeared after formatting.

module exp

go 1.13

require foo v0.0.0-00010101000000-000000000000

[agnivade]

Btw, your What did you do? section is wrong. The command is go mod edit -fmt, not go mod tidy -fmt as you have correctly mentioned in the title.

[0xmohit]

Btw, your What did you do? section is wrong. The command is go mod edit -fmt, not go mod tidy -fmt as you have correctly mentioned in the title.

It was a typo and was meant to be go mod edit -fmt.