cmd/go: add bug command

This is a slightly rough, skeletal implementation.
We will polish and add to it through use.

.github/ISSUE_TEMPLATE will be updated in a
separate CL.

Fixes #16635

Change-Id: Icf284170d87e61b5b643366c85cffc48f149f730
Reviewed-on: https://go-review.googlesource.com/28485Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/bug.go

+// Copyright 2016 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.
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"os/exec"
+	"runtime"
+	"strings"
+)
+
+var cmdBug = &Command{
+	Run:       runBug,
+	UsageLine: "bug",
+	Short:     "print information for bug reports",
+	Long: `
+Bug prints information that helps file effective bug reports.
+
+Bugs may be reported at https://golang.org/issue/new.
+	`,
+}
+
+func init() {
+	cmdBug.Flag.BoolVar(&buildV, "v", false, "")
+}
+
+func runBug(cmd *Command, args []string) {
+	inspectGoVersion()
+	fmt.Println("```")
+	fmt.Printf("go version %s %s/%s\n", runtime.Version(), runtime.GOOS, runtime.GOARCH)
+	for _, e := range mkEnv() {
+		fmt.Printf("%s=\"%s\"\n", e.name, e.value)
+	}
+	printOSDetails()
+	printCDetails()
+	fmt.Println("```")
+}
+
+func printOSDetails() {
+	switch runtime.GOOS {
+	case "darwin":
+		printCmdOut("uname -v: ", "uname", "-v")
+		printCmdOut("", "sw_vers")
+	case "linux":
+		printCmdOut("uname -sr: ", "uname", "-sr")
+		printCmdOut("libc:", "/lib/libc.so.6")
+	case "openbsd", "netbsd", "freebsd", "dragonfly":
+		printCmdOut("uname -v: ", "uname", "-v")
+	case "solaris":
+		out, err := ioutil.ReadFile("/etc/release")
+		if err == nil {
+			fmt.Printf("/etc/release: %s\n", out)
+		} else {
+			if buildV {
+				fmt.Printf("failed to read /etc/release: %v\n", err)
+			}
+		}
+	}
+}
+
+func printCDetails() {
+	printCmdOut("lldb --version: ", "lldb", "--version")
+	cmd := exec.Command("gdb", "--version")
+	out, err := cmd.Output()
+	if err == nil {
+		// There's apparently no combination of command line flags
+		// to get gdb to spit out its version without the license and warranty.
+		// Print up to the first newline.
+		idx := bytes.Index(out, []byte{'\n'})
+		line := out[:idx]
+		line = bytes.TrimSpace(line)
+		fmt.Printf("gdb --version: %s\n", line)
+	} else {
+		if buildV {
+			fmt.Printf("failed to run gdb --version: %v\n", err)
+		}
+	}
+}
+
+func inspectGoVersion() {
+	resp, err := http.Get("https://golang.org/VERSION?m=text")
+	if err != nil {
+		if buildV {
+			fmt.Printf("failed to GET golang.org/VERSION: %v\n", err)
+		}
+		return
+	}
+	defer resp.Body.Close()
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		if buildV {
+			fmt.Printf("failed to read from golang.org/VERSION: %v\n", err)
+		}
+		return
+	}
+
+	// golang.org/VERSION currently returns a whitespace-free string,
+	// but just in case, protect against that changing.
+	// Similarly so for runtime.Version.
+	release := string(bytes.TrimSpace(body))
+	vers := strings.TrimSpace(runtime.Version())
+
+	if vers == release {
+		// Up to date
+		return
+	}
+
+	// Devel version or outdated release. Either way, this request is apropos.
+	fmt.Printf("Please check whether the issue also reproduces on the latest release, %s.\n\n", release)
+}
+
+// printCmdOut prints the output of running the given command.
+// It ignores failures; 'go bug' is best effort.
+func printCmdOut(prefix, path string, args ...string) {
+	cmd := exec.Command(path, args...)
+	out, err := cmd.Output()
+	if err != nil {
+		if buildV {
+			fmt.Printf("%s %s: %v\n", path, strings.Join(args, " "), err)
+		}
+		return
+	}
+	fmt.Printf("%s%s\n", prefix, bytes.TrimSpace(out))
+}

src/cmd/go/main.go

@@ -79,6 +79,7 @@ var commands = []*Command{
 	cmdClean,
 	cmdDoc,
 	cmdEnv,
+	cmdBug,
 	cmdFix,
 	cmdFmt,
 	cmdGenerate,