[vpython] Verify environment, named installs.

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/maruel/subcommands"
         "golang.org/x/net/context"
 
         "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"
 )
 
 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{}
+                var cr installCommandRun
+
+                fs := cr.GetFlags()
+                fs.StringVar(&cr.name, "name", cr.name,
+                        "Use this VirtualEnv name, instead of generating one via hash. This will force specification "+
+                                "validation, causing any existing VirtualEnv with this name to be deleted and reprovisioned "+
+                                "if it doesn't match.")
+
+                return &cr
         },
 }
 
 type installCommandRun struct {
         subcommands.CommandRunBase
+
+        name string
 }
 
 func (cr *installCommandRun) Run(app subcommands.Application, args []string, env subcommands.Env) int {
         c := cli.GetContext(app, cr, env)
         a := getApplication(c, args)
+        a.opts.EnvConfig.PruneThreshold = 0 // Don't prune on install.
+        a.opts.EnvConfig.OverrideName = cr.name
 
         return run(c, func(c context.Context) error {
                 err := venv.With(c, a.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 environment.")
                 return nil
         })
 }