1 files changed, 90 insertions, 0 deletions
diff --git a/libgo/go/cmd/go/internal/modcmd/tidy.go b/libgo/go/cmd/go/internal/modcmd/tidy.go
new file mode 100644
index 00000000000..f2063a9ea60
--- /dev/null
+++ b/libgo/go/cmd/go/internal/modcmd/tidy.go
@@ -0,0 +1,90 @@
+// 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 tidy
+
+package modcmd
+
+import (
+	"fmt"
+	"os"
+
+	"cmd/go/internal/base"
+	"cmd/go/internal/cfg"
+	"cmd/go/internal/modfetch"
+	"cmd/go/internal/modload"
+	"cmd/go/internal/module"
+)
+
+var cmdTidy = &base.Command{
+	UsageLine: "go mod tidy [-v]",
+	Short:     "add missing and remove unused modules",
+	Long: `
+Tidy makes sure go.mod matches the source code in the module.
+It adds any missing modules necessary to build the current module's
+packages and dependencies, and it removes unused modules that
+don't provide any relevant packages. It also adds any missing entries
+to go.sum and removes any unnecessary ones.
+
+The -v flag causes tidy to print information about removed modules
+to standard error.
+	`,
+}
+
+func init() {
+	cmdTidy.Run = runTidy // break init cycle
+	cmdTidy.Flag.BoolVar(&cfg.BuildV, "v", false, "")
+}
+
+func runTidy(cmd *base.Command, args []string) {
+	if len(args) > 0 {
+		base.Fatalf("go mod tidy: no arguments allowed")
+	}
+
+	// LoadALL adds missing modules.
+	// Remove unused modules.
+	used := make(map[module.Version]bool)
+	for _, pkg := range modload.LoadALL() {
+		used[modload.PackageModule(pkg)] = true
+	}
+	used[modload.Target] = true // note: LoadALL initializes Target
+
+	inGoMod := make(map[string]bool)
+	for _, r := range modload.ModFile().Require {
+		inGoMod[r.Mod.Path] = true
+	}
+
+	var keep []module.Version
+	for _, m := range modload.BuildList() {
+		if used[m] {
+			keep = append(keep, m)
+		} else if cfg.BuildV && inGoMod[m.Path] {
+			fmt.Fprintf(os.Stderr, "unused %s\n", m.Path)
+		}
+	}
+	modload.SetBuildList(keep)
+	modTidyGoSum() // updates memory copy; WriteGoMod on next line flushes it out
+	modload.WriteGoMod()
+}
+
+// modTidyGoSum resets the go.sum file content
+// to be exactly what's needed for the current go.mod.
+func modTidyGoSum() {
+	// Assuming go.sum already has at least enough from the successful load,
+	// we only have to tell modfetch what needs keeping.
+	reqs := modload.Reqs()
+	keep := make(map[module.Version]bool)
+	var walk func(module.Version)
+	walk = func(m module.Version) {
+		keep[m] = true
+		list, _ := reqs.Required(m)
+		for _, r := range list {
+			if !keep[r] {
+				walk(r)
+			}
+		}
+	}
+	walk(modload.Target)
+	modfetch.TrimGoSum(keep)
+}