Move driver validation before driver selection

If a user passes in a driver via --vm-driver or --driver, then we should make sure it matches the preexisting cluster (if one exists) before we try and get information about the driver. This avoids confusing logs where we tell the user we're using the preexisting driver but then error out because they specified a different driver.

Author: Priya Wadhwa

cmd/minikube/cmd/start.go

@@ -294,6 +294,7 @@ func runStart(cmd *cobra.Command, args []string) {
 		exit.WithCodeT(exit.Data, "Unable to load config: {{.error}}", out.V{"error": err})
 	}
 
+	validateSpecifiedDriver(existing)
 	ds := selectDriver(existing)
 	driverName := ds.Name
 	glog.Infof("selected driver: %s", driverName)
@@ -482,36 +483,20 @@ func selectDriver(existing *config.ClusterConfig) registry.DriverState {
 	return pick
 }
 
-// validateDriver validates that the selected driver appears sane, exits if not
-func validateDriver(ds registry.DriverState, existing *config.ClusterConfig) {
-	name := ds.Name
-	glog.Infof("validating driver %q against %+v", name, existing)
-	if !driver.Supported(name) {
-		exit.WithCodeT(exit.Unavailable, "The driver {{.experimental}} '{{.driver}}' is not supported on {{.os}}", out.V{"driver": name, "os": runtime.GOOS})
+// validateSpecifiedDriver makes sure that if a user has passed in a driver
+// it matches the existing cluster if there is one
+func validateSpecifiedDriver(existing *config.ClusterConfig) {
+	if existing == nil {
+		return
 	}
-
-	st := ds.State
-	glog.Infof("status for %s: %+v", name, st)
-
-	if st.Error != nil {
-		out.ErrLn("")
-
-		out.WarningT("'{{.driver}}' driver reported an issue: {{.error}}", out.V{"driver": name, "error": st.Error})
-		out.ErrT(out.Tip, "Suggestion: {{.fix}}", out.V{"fix": translate.T(st.Fix)})
-		if st.Doc != "" {
-			out.ErrT(out.Documentation, "Documentation: {{.url}}", out.V{"url": st.Doc})
-		}
-		out.ErrLn("")
-
-		if !st.Installed && !viper.GetBool(force) {
-			if existing != nil && name == existing.Driver {
-				exit.WithCodeT(exit.Unavailable, "{{.driver}} does not appear to be installed, but is specified by an existing profile. Please run 'minikube delete' or install {{.driver}}", out.V{"driver": name})
-			}
-			exit.WithCodeT(exit.Unavailable, "{{.driver}} does not appear to be installed", out.V{"driver": name})
-		}
+	old := existing.Driver
+	var requested string
+	if d := viper.GetString("driver"); d != "" {
+		requested = d
+	} else if d := viper.GetString("vm-driver"); d != "" {
+		requested = d
 	}
-
-	if existing == nil {
+	if old == requested {
 		return
 	}
 
@@ -525,33 +510,58 @@ func validateDriver(ds registry.DriverState, existing *config.ClusterConfig) {
 	if err != nil {
 		exit.WithError("Error getting primary cp", err)
 	}
-
 	machineName := driver.MachineName(*existing, cp)
 	h, err := api.Load(machineName)
 	if err != nil {
 		glog.Warningf("selectDriver api.Load: %v", err)
 		return
 	}
 
-	if h.Driver.DriverName() == name {
-		return
-	}
-
-	out.ErrT(out.Conflict, `The existing "{{.profile_name}}" VM that was created using the "{{.old_driver}}" driver, and is incompatible with the "{{.driver}}" driver.`,
-		out.V{"profile_name": machineName, "driver": name, "old_driver": h.Driver.DriverName()})
+	out.ErrT(out.Conflict, `The existing "{{.profile_name}}" VM was created using the "{{.old_driver}}" driver, and is incompatible with the "{{.driver}}" driver.`,
+		out.V{"profile_name": machineName, "driver": requested, "old_driver": h.Driver.DriverName()})
 
 	out.ErrT(out.Workaround, `To proceed, either:
 
-    1) Delete the existing "{{.profile_name}}" cluster using: '{{.command}} delete'
+1) Delete the existing "{{.profile_name}}" cluster using: '{{.command}} delete'
 
-    * or *
+* or *
 
-    2) Start the existing "{{.profile_name}}" cluster using: '{{.command}} start --driver={{.old_driver}}'
-	`, out.V{"command": minikubeCmd(), "old_driver": h.Driver.DriverName(), "profile_name": machineName})
+2) Start the existing "{{.profile_name}}" cluster using: '{{.command}} start --driver={{.old_driver}}'
+`, out.V{"command": minikubeCmd(), "old_driver": h.Driver.DriverName(), "profile_name": machineName})
 
 	exit.WithCodeT(exit.Config, "Exiting.")
 }
 
+// validateDriver validates that the selected driver appears sane, exits if not
+func validateDriver(ds registry.DriverState, existing *config.ClusterConfig) {
+	name := ds.Name
+	glog.Infof("validating driver %q against %+v", name, existing)
+	if !driver.Supported(name) {
+		exit.WithCodeT(exit.Unavailable, "The driver {{.experimental}} '{{.driver}}' is not supported on {{.os}}", out.V{"driver": name, "os": runtime.GOOS})
+	}
+
+	st := ds.State
+	glog.Infof("status for %s: %+v", name, st)
+
+	if st.Error != nil {
+		out.ErrLn("")
+
+		out.WarningT("'{{.driver}}' driver reported an issue: {{.error}}", out.V{"driver": name, "error": st.Error})
+		out.ErrT(out.Tip, "Suggestion: {{.fix}}", out.V{"fix": translate.T(st.Fix)})
+		if st.Doc != "" {
+			out.ErrT(out.Documentation, "Documentation: {{.url}}", out.V{"url": st.Doc})
+		}
+		out.ErrLn("")
+
+		if !st.Installed && !viper.GetBool(force) {
+			if existing != nil && name == existing.Driver {
+				exit.WithCodeT(exit.Unavailable, "{{.driver}} does not appear to be installed, but is specified by an existing profile. Please run 'minikube delete' or install {{.driver}}", out.V{"driver": name})
+			}
+			exit.WithCodeT(exit.Unavailable, "{{.driver}} does not appear to be installed", out.V{"driver": name})
+		}
+	}
+}
+
 func selectImageRepository(mirrorCountry string, v semver.Version) (bool, string, error) {
 	var tryCountries []string
 	var fallback string