vpython: Add application entry point.

vpython/application/subcommand_install.go

Index: vpython/application/subcommand_install.go
diff --git a/vpython/application/subcommand_install.go b/vpython/application/subcommand_install.go
new file mode 100644
index 0000000000000000000000000000000000000000..c8e58dccd5d1aaf8ba1dde088f2a9907343bcd08
--- /dev/null
+++ b/vpython/application/subcommand_install.go
@@ -0,0 +1,46 @@
+// 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
+	})
+}