Add beginnings of new cr command

go/src/infra/tools/cr/cmd/firstrun/firstrun_unix.go

Index: go/src/infra/tools/cr/cmd/firstrun/firstrun_unix.go
diff --git a/go/src/infra/tools/cr/cmd/firstrun/firstrun_unix.go b/go/src/infra/tools/cr/cmd/firstrun/firstrun_unix.go
new file mode 100644
index 0000000000000000000000000000000000000000..3f3618773bf6c357c92b6e1eec11bcfe74ac3005
--- /dev/null
+++ b/go/src/infra/tools/cr/cmd/firstrun/firstrun_unix.go
@@ -0,0 +1,55 @@
+// 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.
+
+// +build !windows
+
+// unix-specific function implementations for the firstrun subcommand.
+
+package firstrun
+
+import (
+	"errors"
+)
+
+var executableName = "cr"
+
+// firstrunPromptInstallDir prompts the user for a directory path to install cr.
+func firstrunPromptInstallDir() (string, error) {
+	return "", errors.New("firstrun_unix.firstrunPromptInstallDir not yet implemented")
+	// TODO(agable): Figure out a sane place to suggest.
+	// TODO(agable): Suggest it and ask the user for an alternative.
+	// TODO(agable): Check that the chosen directory makes sense.
+}
+
+// firstrunInitInstallDir sets up the selected directory to house cr. It creates
+// the modules/ and bin/ subdirectories, places the cr executable in the
+// top level, and symlinks it into bin/.
+func firstrunInitInstallDir(dir string) error {
+	return errors.New("firstrun_unix.firstrunInitInstallDir not yet implemented")
+	// TODO(agable): Create the cr/ directory.
+	// TODO(agable): Copy this executable into the cr/ directory.
+	// TODO(agable): Create the bin/ subdirectory.
+	// TODO(agable): Add a symlink to the cr executable in the bin/ subdirectory.
+	// TODO(agable): Create the modules/ subdirectory.
+}
+
+// firstrunUpdatePath finds the rcfile in which $PATH is set, sees if it can
+// automatically update it, and prompts the user for permission to do so.
+func firstrunUpdatePath(dir string) error {
+	return errors.New("firstrun_unix.firstrunUpdatePath not yet implemented")
+	// TODO(agable): Detect the user's default shell.
+	// TODO(agable): Find their shell's rcfile.
+	// TODO(agable): Find lines modifying $PATH in that file.
+	// TODO(agable): Fine a line mentioning depot_tools.
+	// TODO(agable): Produce a git-style diff adding the install bin/ dir after than line.
+	// TODO(agable): Prompt the user to see if they want to apply that diff.
+	// TODO(agable): Apply the diff, or print instructions on how to do it manually.
+}
+
+// firstrunPrintUpdatePathInstructions prints instructions for the user to
+// update their $PATH manually. This is used if updatePath fails, or if the user
+// declines to have their rcfile updated automatically.
+func firstrunPrintUpdatePathInstructions() error {
+	return errors.New("firstrun_unix.firstrunPrintUpdatePathInstructions not yet implemented")
+}