cmd/go: split out cmd/go/internal/bug

This is one CL in a long sequence of changes to break up the
go command from one package into a plausible group of packages.

This sequence is concerned only with moving code, not changing
or cleaning up code. There will still be more cleanup after this sequence.

The entire sequence will be submitted together: it is not a goal
for the tree to build at every step.

For #18653.

Change-Id: I05629567cc33fef41bc74eba4f7ff66e4851343c
Reviewed-on: https://go-review.googlesource.com/36203
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/go/internal/bug/bug.go

@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package main
+// Package bug implements the ``go bug'' command.
+package bug
 
 import (
 	"bytes"
@@ -18,11 +19,11 @@ import (
 
 	"cmd/go/internal/base"
 	"cmd/go/internal/cfg"
-	envcmd "cmd/go/internal/env"
+	"cmd/go/internal/envcmd"
 	"cmd/go/internal/web"
 )
 
-var cmdBug = &base.Command{
+var CmdBug = &base.Command{
 	Run:       runBug,
 	UsageLine: "bug",
 	Short:     "start a bug report",
@@ -33,7 +34,7 @@ The report includes useful system information.
 }
 
 func init() {
-	cmdBug.Flag.BoolVar(&cfg.BuildV, "v", false, "")
+	CmdBug.Flag.BoolVar(&cfg.BuildV, "v", false, "")
 }
 
 func runBug(cmd *base.Command, args []string) {
@@ -43,7 +44,7 @@ func runBug(cmd *base.Command, args []string) {
 	fmt.Fprint(&buf, "#### System details\n\n")
 	fmt.Fprintln(&buf, "```")
 	fmt.Fprintf(&buf, "go version %s %s/%s\n", runtime.Version(), runtime.GOOS, runtime.GOARCH)
-	env := cfg.NewEnv
+	env := cfg.CmdEnv
 	env = append(env, envcmd.ExtraEnvVars()...)
 	for _, e := range env {
 		// Hide the TERM environment variable from "go bug".

src/cmd/go/main.go

@@ -14,6 +14,7 @@ import (
 	"strings"
 
 	"cmd/go/internal/base"
+	"cmd/go/internal/bug"
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/env"
 	fmtcmd "cmd/go/internal/fmt"
@@ -29,7 +30,7 @@ func init() {
 		cmdClean,
 		cmdDoc,
 		env.CmdEnv,
-		cmdBug,
+		bug.CmdBug,
 		cmdFix,
 		fmtcmd.CmdFmt,
 		cmdGenerate,