Add beginnings of new cr command

go/src/infra/tools/cr/lib/terminal/terminal.go

+// Copyright 2016 The Chromium 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 terminal provides utilities for printing to and reading user input
+// from an interactive terminal.
+package terminal
+
+import (
+        "bufio"
+        "fmt"
+        "os"
+)
+
+var showDebug = false
+
+// SetDebug sets the internal state to start/stop printing lines sent to Debug.

[seanmccullough1, 2016/04/29 00:54:37]

Just make var ShowDebug exported and get rid of this setter. Though, see comment
below about whether or not you really need this at all.

[agable, 2016/05/05 23:59:43]

Done. See reply below for whether or not this package is necessary at all.

+func SetDebug(show bool) {
+        showDebug = show
+}
+
+// Print prints the given format string (and arguments) to standard out.
+func Print(format string, args ...interface{}) {

[seanmccullough1, 2016/04/29 00:54:37]

Just use fmt.Printf (or log.Printf)?

+        fmt.Printf(format, args)
+}
+
+// Debug is the same as Print, but only produces output if SetDebug(true)
+// has been called.
+func Debug(format string, args ...interface{}) {

[seanmccullough1, 2016/04/29 00:54:37]

I'd just use the standard logging packages for now, and make sure to remove
debug Printf statements from your CL before submitting.

[agable, 2016/05/05 23:59:43]

Command line tools without verbosity levels make me sad. In the default case,
you want to print as little as possible to convince the user that useful work is
being done. In the failure case, you need to print checkpoints and interesting
information so that the user has a useful log they can provide to you. I felt it
was important to get some form of normal/verbose printing in here early on, so
that I could use it without having to think about it later.

These aren't for my personal debugging -- I use Printf for that and remove it
before sending the CL. These are for the actual end-user.

+        if showDebug {
+                fmt.Printf(format, args)
+        }
+}
+
+// Prompt prints a string to standard out, then waits for a single line
+// of user input and returns it.
+func Prompt(prompt string) string {
+        fmt.Print(prompt)
+        reader := bufio.NewReader(os.Stdin)
+        text, _ := reader.ReadString('\n')
+        return text
+}