[vpython] Verify environment, named installs.

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
index b9549f84e848090da73f0f26cbc11f5bad79bc6d..8e60d9a8dbeb1df0d6f62223ee6b6f5935fb8f1b 100644
--- a/vpython/application/subcommand_install.go
+++ b/vpython/application/subcommand_install.go
@@ -21,17 +21,29 @@ var subcommandInstall = &subcommands.Command{
 	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 {