vpython: Add application entry point.

vpython/application/subcommand_install.go

+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package application
+
+import (
+        "github.com/luci/luci-go/common/cli"
+        "github.com/luci/luci-go/common/errors"
+        "github.com/luci/luci-go/common/logging"
+        "github.com/luci/luci-go/vpython/venv"
+
+        "github.com/maruel/subcommands"
+        "golang.org/x/net/context"
+)
+
+var subcommandInstall = &subcommands.Command{
+        UsageLine: "install",
+        ShortDesc: "installs the configured VirtualEnv",
+        LongDesc:  "installs the configured VirtualEnv, but doesn't run any associated commands",
+        Advanced:  false,
+        CommandRun: func() subcommands.CommandRun {
+                return &installCommandRun{}
+        },
+}
+
+type installCommandRun struct {
+        subcommands.CommandRunBase
+}
+
+func (cr *installCommandRun) Run(app subcommands.Application, args []string, env subcommands.Env) int {
+        c := cli.GetContext(app, cr, env)
+        cfg := getConfig(c)
+
+        return run(c, func(c context.Context) error {
+                err := venv.With(c, cfg.Opts.EnvConfig, false, func(context.Context, *venv.Env) error {
+                        return nil
+                })
+                if err != nil {
+                        return errors.Annotate(err).Reason("failed to setup the environment").Err()
+                }
+
+                logging.Infof(c, "Successfully setup the enviornment.")
+                return nil
+        })
+}