1 files changed, 35 insertions, 10 deletions

diff --git a/libgo/go/cmd/go/internal/modcmd/edit.go b/libgo/go/cmd/go/internal/modcmd/edit.go
index 5fea3e48e08..5066e4ddf75 100644
--- a/libgo/go/cmd/go/internal/modcmd/edit.go
+++ b/libgo/go/cmd/go/internal/modcmd/edit.go
@@ -7,6 +7,7 @@
 package modcmd
 
 import (
+	"bytes"
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
@@ -15,6 +16,7 @@ import (
 	"strings"
 
 	"cmd/go/internal/base"
+	"cmd/go/internal/modfetch"
 	"cmd/go/internal/modfile"
 	"cmd/go/internal/modload"
 	"cmd/go/internal/module"
@@ -62,6 +64,8 @@ The -require, -droprequire, -exclude, -dropexclude, -replace,
 and -dropreplace editing flags may be repeated, and the changes
 are applied in the order given.
 
+The -go=version flag sets the expected Go language version.
+
 The -print flag prints the final go.mod in its text format instead of
 writing it back to go.mod.
 
@@ -74,7 +78,8 @@ writing it back to go.mod. The JSON output corresponds to these Go types:
 	}
 
 	type GoMod struct {
-		Module Module
+		Module  Module
+		Go      string
 		Require []Require
 		Exclude []Module
 		Replace []Replace
@@ -102,8 +107,8 @@ by invoking 'go mod edit' with -require, -exclude, and so on.
 }
 
 var (
-	editFmt = cmdEdit.Flag.Bool("fmt", false, "")
-	// editGo     = cmdEdit.Flag.String("go", "", "")
+	editFmt    = cmdEdit.Flag.Bool("fmt", false, "")
+	editGo     = cmdEdit.Flag.String("go", "", "")
 	editJSON   = cmdEdit.Flag.Bool("json", false, "")
 	editPrint  = cmdEdit.Flag.Bool("print", false, "")
 	editModule = cmdEdit.Flag.String("module", "", "")
@@ -131,6 +136,7 @@ func init() {
 func runEdit(cmd *base.Command, args []string) {
 	anyFlags :=
 		*editModule != "" ||
+			*editGo != "" ||
 			*editJSON ||
 			*editPrint ||
 			*editFmt ||
@@ -151,8 +157,7 @@ func runEdit(cmd *base.Command, args []string) {
 	if len(args) == 1 {
 		gomod = args[0]
 	} else {
-		modload.MustInit()
-		gomod = filepath.Join(modload.ModRoot, "go.mod")
+		gomod = filepath.Join(modload.ModRoot(), "go.mod")
 	}
 
 	if *editModule != "" {
@@ -161,7 +166,11 @@ func runEdit(cmd *base.Command, args []string) {
 		}
 	}
 
-	// TODO(rsc): Implement -go= once we start advertising it.
+	if *editGo != "" {
+		if !modfile.GoVersionRE.MatchString(*editGo) {
+			base.Fatalf(`go mod: invalid -go option; expecting something like "-go 1.12"`)
+		}
+	}
 
 	data, err := ioutil.ReadFile(gomod)
 	if err != nil {
@@ -174,7 +183,13 @@ func runEdit(cmd *base.Command, args []string) {
 	}
 
 	if *editModule != "" {
-		modFile.AddModuleStmt(modload.CmdModModule)
+		modFile.AddModuleStmt(*editModule)
+	}
+
+	if *editGo != "" {
+		if err := modFile.AddGoStmt(*editGo); err != nil {
+			base.Fatalf("go: internal error: %v", err)
+		}
 	}
 
 	if len(edits) > 0 {
@@ -190,17 +205,23 @@ func runEdit(cmd *base.Command, args []string) {
 		return
 	}
 
-	data, err = modFile.Format()
+	out, err := modFile.Format()
 	if err != nil {
 		base.Fatalf("go: %v", err)
 	}
 
 	if *editPrint {
-		os.Stdout.Write(data)
+		os.Stdout.Write(out)
 		return
 	}
 
-	if err := ioutil.WriteFile(gomod, data, 0666); err != nil {
+	unlock := modfetch.SideLock()
+	defer unlock()
+	lockedData, err := ioutil.ReadFile(gomod)
+	if err == nil && !bytes.Equal(lockedData, data) {
+		base.Fatalf("go: go.mod changed during editing; not overwriting")
+	}
+	if err := ioutil.WriteFile(gomod, out, 0666); err != nil {
 		base.Fatalf("go: %v", err)
 	}
 }
@@ -344,6 +365,7 @@ func flagDropReplace(arg string) {
 // fileJSON is the -json output data structure.
 type fileJSON struct {
 	Module  module.Version
+	Go      string `json:",omitempty"`
 	Require []requireJSON
 	Exclude []module.Version
 	Replace []replaceJSON
@@ -364,6 +386,9 @@ type replaceJSON struct {
 func editPrintJSON(modFile *modfile.File) {
 	var f fileJSON
 	f.Module = modFile.Module.Mod
+	if modFile.Go != nil {
+		f.Go = modFile.Go.Version
+	}
 	for _, r := range modFile.Require {
 		f.Require = append(f.Require, requireJSON{Path: r.Mod.Path, Version: r.Mod.Version, Indirect: r.Indirect})
 	}