src/cmd/go/internal/modcmd/graph.go

// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// go mod graph

package modcmd

import (
	"bufio"
	"context"
	"os"

	"cmd/go/internal/base"
	"cmd/go/internal/modload"

	"golang.org/x/mod/module"
)

var cmdGraph = &base.Command{
	UsageLine: "go mod graph [-go=version]",
	Short:     "print module requirement graph",
	Long: `
Graph prints the module requirement graph (with replacements applied)
in text form. Each line in the output has two space-separated fields: a module
and one of its requirements. Each module is identified as a string of the form
path@version, except for the main module, which has no @version suffix.

The -go flag causes graph to report the module graph as loaded by by the
given Go version, instead of the version indicated by the 'go' directive
in the go.mod file.

See https://golang.org/ref/mod#go-mod-graph for more about 'go mod graph'.
	`,
	Run: runGraph,
}

var (
	graphGo goVersionFlag
)

func init() {
	cmdGraph.Flag.Var(&graphGo, "go", "")
	base.AddModCommonFlags(&cmdGraph.Flag)
}

func runGraph(ctx context.Context, cmd *base.Command, args []string) {
	if len(args) > 0 {
		base.Fatalf("go mod graph: graph takes no arguments")
	}
	modload.ForceUseModules = true
	modload.RootMode = modload.NeedRoot
	mg := modload.LoadModGraph(ctx, graphGo.String())

	w := bufio.NewWriter(os.Stdout)
	defer w.Flush()

	format := func(m module.Version) {
		w.WriteString(m.Path)
		if m.Version != "" {
			w.WriteString("@")
			w.WriteString(m.Version)
		}
	}

	mg.WalkBreadthFirst(func(m module.Version) {
		reqs, _ := mg.RequiredBy(m)
		for _, r := range reqs {
			format(m)
			w.WriteByte(' ')
			format(r)
			w.WriteByte('\n')
		}
	})
}