1 files changed, 73 insertions, 0 deletions
diff --git a/libgo/go/cmd/go/internal/modcmd/graph.go b/libgo/go/cmd/go/internal/modcmd/graph.go
new file mode 100644
index 00000000000..5825c6d8ca8
--- /dev/null
+++ b/libgo/go/cmd/go/internal/modcmd/graph.go
@@ -0,0 +1,73 @@
+// 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"
+	"os"
+	"sort"
+
+	"cmd/go/internal/base"
+	"cmd/go/internal/modload"
+	"cmd/go/internal/module"
+	"cmd/go/internal/par"
+)
+
+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.
+	`,
+	Run: runGraph,
+}
+
+func runGraph(cmd *base.Command, args []string) {
+	if len(args) > 0 {
+		base.Fatalf("go mod graph: graph takes no arguments")
+	}
+	modload.LoadBuildList()
+
+	reqs := modload.MinReqs()
+	format := func(m module.Version) string {
+		if m.Version == "" {
+			return m.Path
+		}
+		return m.Path + "@" + m.Version
+	}
+
+	// Note: using par.Work only to manage work queue.
+	// No parallelism here, so no locking.
+	var out []string
+	var deps int // index in out where deps start
+	var work par.Work
+	work.Add(modload.Target)
+	work.Do(1, func(item interface{}) {
+		m := item.(module.Version)
+		list, _ := reqs.Required(m)
+		for _, r := range list {
+			work.Add(r)
+			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()
+}