1 files changed, 84 insertions, 0 deletions
diff --git a/src/cmd/go/internal/modcmd/graph.go b/src/cmd/go/internal/modcmd/graph.go
new file mode 100644
index 0000000..a88e9ef
--- /dev/null
+++ b/src/cmd/go/internal/modcmd/graph.go
@@ -0,0 +1,84 @@
+// 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"
+	"sort"
+
+	"cmd/go/internal/base"
+	"cmd/go/internal/modload"
+
+	"golang.org/x/mod/module"
+)
+
+var cmdGraph = &base.Command{
+	UsageLine: "go mod graph",
+	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.
+
+See https://golang.org/ref/mod#go-mod-graph for more about 'go mod graph'.
+	`,
+	Run: runGraph,
+}
+
+func init() {
+	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
+	modload.LoadAllModules(ctx)
+
+	reqs := modload.MinReqs()
+	format := func(m module.Version) string {
+		if m.Version == "" {
+			return m.Path
+		}
+		return m.Path + "@" + m.Version
+	}
+
+	var out []string
+	var deps int // index in out where deps start
+	seen := map[module.Version]bool{modload.Target: true}
+	queue := []module.Version{modload.Target}
+	for len(queue) > 0 {
+		var m module.Version
+		m, queue = queue[0], queue[1:]
+		list, _ := reqs.Required(m)
+		for _, r := range list {
+			if !seen[r] {
+				queue = append(queue, r)
+				seen[r] = true
+			}
+			out = append(out, format(m)+" "+format(r)+"\n")
+		}
+		if m == modload.Target {
+			deps = len(out)
+		}
+	}
+
+	sort.Slice(out[deps:], func(i, j int) bool {
+		return out[deps+i][0] < out[deps+j][0]
+	})
+
+	w := bufio.NewWriter(os.Stdout)
+	for _, line := range out {
+		w.WriteString(line)
+	}
+	w.Flush()
+}