Repository: go
Issue: x/mod/modfile: AddNewRequire doesn't put direct dependencies in the first block
Labels: NeedsDecision,modules

### Go version

go version go1.23.0 linux/amd64

### Output of `go env` in your module/workspace:

```shell
GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/steveh/.cache/go-build'
GOENV='/home/steveh/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/steveh/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/steveh/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.23.0'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/steveh/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/steveh/code/github.com/rocketsciencegg/congestion-control/tools/go.mod'
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 -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build155249492=/tmp/go-build -gno-record-gcc-switches'
```


### What did you do?

Use [AddNewRequire](https://pkg.go.dev/golang.org/x/mod@v0.20.0/modfile#File.AddNewRequire) to add new requires.

```go
package main

import (
	"testing"

	"github.com/stretchr/testify/require"
	"golang.org/x/mod/modfile"
	"golang.org/x/mod/module"
)

var testFile = `module test

go 1.23.0

require (
	github.com/test/test1 v0.1.0
	github.com/test/test2 v0.1.0
)

require (
	github.com/test/test3 v0.1.0 // indirect
)
`

var expected = `module test

go 1.23.0

require (
	github.com/foo/direct1 v0.1.1
	github.com/foo/direct2 v0.1.2
	github.com/test/test1 v0.1.0
	github.com/test/test2 v0.1.0
)

require (
	github.com/foo/indirect1 v0.2.1 // indirect
	github.com/foo/indirect2 v0.2.2 // indirect
	github.com/test/test3 v0.1.0 // indirect
)
`

func TestAddRequire(t *testing.T) {
	file, err := modfile.Parse("go.mod", []byte(testFile), nil)
	require.NoError(t, err)

	file.AddNewRequire("github.com/foo/indirect2", "v0.2.2", true)
	file.AddNewRequire("github.com/foo/direct2", "v0.1.2", false)
	file.AddNewRequire("github.com/foo/direct1", "v0.1.1", false)
	file.AddNewRequire("github.com/foo/indirect1", "v0.2.1", true)

	file.Cleanup()
	file.SortBlocks()

	data, err := file.Format()
	require.NoError(t, err)
	require.Equal(t, expected, string(data))
}
```


### What did you see happen?

Direct requires should be added to first require block, indirect requires should be added to second block.

### What did you expect to see?

When using `AddNewRequire`, requires are added to the last block. This is the documented behaviour, but other go tools such as `go mod tidy` maintain two blocks, so this use the same approach.

It seems possible to use `SetRequireSeparateIndirect` to replicate the desired behaviour but that was far from obvious.

If nothing else reference in `AddNewRequire` and `Addequire` to  `SetRequireSeparateIndirect` would help users fine the right functionality, but ideally `AddNewRequire` and `AddRequire` should function as expected.

If a user isn't aware of the two block rule then using this will result in a file that `go mod tidy` handles badly, in some cases resulting in three blocks instead of two.