cmd/go: `go mod tidy` leaves trailing empty lines in `require` blocks

[thaJeztah]

Go version

go version go1.23.3 linux/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/root/.cache/go-build'
GOENV='/root/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_arm64'
GOVCS=''
GOVERSION='go1.23.3'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/root/.config/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2955114020=/tmp/go-build -gno-record-gcc-switches'

What did you do?

Ran go mod tidy with a go.mod that contained a stray empty line in a require block

Reproduction steps

Create a minimal module with at least one dependency

mkdir tidy && cd tidy

cat > main.go <<'EOF'
package main

import (
	"fmt"

	"golang.org/x/time/rate"
)
var Foo = rate.Limit

func main() {
	fmt.Println("hello")
}
EOF

Create a go.mod with trailing empty lines in the require section;

cat > go.mod <<'EOF'
module tidy

go 1.23.0

require (
	"golang.org/x/time" v0.8.0




)
EOF

Run go mod tidy;

go mod tidy

Check the content of go.mod, and observe that an empty line is left behind in the require section;

cat go.mod
module tidy

go 1.23.0

require (
	golang.org/x/time v0.8.0

)

What did you see happen?

The empty line was kept even after running go mod tidy

What did you expect to see?

The empty line to be removed.

[gabyhelp]

Related Issues

• cmd/go: 'mod tidy' sometimes adds new, unnecessary require sections #67948 (closed)
• cmd/go: 'go mod tidy' removes needed requirements when the module directory ends in '/testdata' #28481 (closed)
• cmd/go: mod tidy removes lines that build seems to need #31248 (closed)
• cmd/go: 'mod tidy' chooses points in requirement cycles that differ from other subcommands #34086 (closed)
• cmd/go: mod tidy doesn't remove unused dependencies in go.sum, in same cases #37842 (closed)
• cmd/go: go mod tidy misses adding certain lines to go.sum #28129 (closed)
• cmd/go: trim go.sum without adding module requirements #29800
• cmd/go: 'go mod tidy' retains sums for modules in the requirement graph but not the build list #39424 (closed)
• cmd/go: 'go mod tidy' may delete comments on require blocks #47563 (closed)

Related Code Changes

• [release-branch.go1.13] cmd/go/internal/modfile: remove preceding empty lines when setting require

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[mknyszek]

CC @golang/tools-team

[Agent-Hellboy]

Hi @seankhliao this looks like a good issue for a beginner like me, and I feel I could learn a lot from working on it. Can I give it a try if no one else is already on it? Thanks!

[matloob]

@Agent-Hellboy Go for it! This would have to wait until go1.25 development starts to get submitted but you could start working on it now.

This would need to be fixed in golang.org/x/mod/modfile in the mod repo. See this example: https://go.dev/play/p/Dl2Kix5Sq67

When we format the file, it should remove the blank line but it doesn't. Once we fix that and vendor the fix in go mod tidy will be fixed too.

[Agent-Hellboy]

Hi @matloob , thanks! I have a doubt. I cloned modfile, made changes, and used my local path in imports of modfile the other day, but I was not able to build the binary. It was giving a weird error as modfile is not there in vendor. Do I need to clone it in a specific place?

I guess Go is assuming it’s a standalone library inside the Go project. What’s the flow to test the changes made inside the modfile repo?

[matloob]

@Agent-Hellboy So to test changes in the go command that depend on changes in the golang.org/x/mod repo you need to do the following:

1. Add a replace directive to the src/cmd/go.mod in your go repo pointing to your modified x/mod repo.
2. Run go mod vendor in the src/cmd directory in the go repo to vendor in your changes in to the src/cmd/vendor directory.

You will then have the updated changes to x/mod vendored in for use by cmd/go.

You will need to rerun go mod vendor whenever you make new changes in the x/mod repo so that you can try them out.

[Agent-Hellboy]

Thanks @matloob , I am able to build and test.

what about updating https://go.dev/doc/contribute#where, or is it documented somewhere else ?

[Agent-Hellboy]

Hi @matloob , I have added a PR golang/mod#22 , I am ignoring the newline during parsing of required block itself, looks like there are cleanup methods for all block but ignoring at parsing stage was easy.

Tests are passing , I hope it didn't introduce any regression

[gopherbot]

Change https://go.dev/cl/634875 mentions this issue: modfile: fix trailing empty lines in require blocks